PATENT DOCUMENT

Publication Number: US-12126264-B1
Application Number: US-201916720749-A
Country: US
Kind Code: B1

Title: Current sensors for power converters

Abstract:
Systems and methods for current sensing are described. For example, a system may include a transformer including a winding that connects a first tap and a second tap; a circuit board; a first trace on a layer of the circuit board, wherein the first trace connects the first tap to a rectifier; a coil including one or more turns of trace on the layer of the circuit board, adjacent to the first trace; and a measurement circuit configured to estimate current flowing in the first trace based on voltage across the coil.

Claims:
What is claimed is: 
     
       1. A power converter comprising:
 a transformer including a winding that connects a first tap and a second tap; 
 a circuit board; 
 a first trace on a layer of the circuit board, wherein the first trace connects the first tap to a rectifier; 
 a first coil including one or more turns of trace on the layer of the circuit board, adjacent to the first trace, wherein the first coil is isolated from the transformer; 
 a second coil including one or more turns of trace on an additional layer of the circuit board, stacked vertically with the first coil; and 
 a measurement circuit configured to estimate current flowing in the first trace based on voltage across the first coil, wherein the second coil is connected in series with the first coil between terminals of the measurement circuit to capture more flux and induce more voltage. 
 
     
     
       2. The power converter of  claim 1 , wherein the first coil includes two or more turns arranged in a spiral. 
     
     
       3. The power converter of  claim 1 , wherein an edge of the first coil is within one millimeter of an edge of the first trace. 
     
     
       4. The power converter of  claim 1 , further comprising:
 a third coil including one or more turns of trace on the layer of the circuit board, adjacent to the first trace, on an opposite side of the first trace from the first coil, wherein the third coil is connected in series with the first coil between terminals of the measurement circuit. 
 
     
     
       5. The power converter of  claim 4 , wherein the first coil and the third coil have opposite winding directions. 
     
     
       6. The power converter of  claim 1 , comprising:
 a second trace on the layer of the circuit board, wherein the second trace connects the second tap to the rectifier; and 
 a third coil including one or more turns of trace on the layer of the circuit board, adjacent to the second trace, wherein the third coil is connected in series with the first coil between terminals of the measurement circuit. 
 
     
     
       7. The power converter of  claim 1 , comprising:
 a third coil including one or more turns of trace on the layer of the circuit board, adjacent to the first trace, on a same side of the first trace as the first coil, wherein the third coil is connected in series with the first coil between terminals of the measurement circuit. 
 
     
     
       8. The power converter of  claim 1 , comprising:
 a second trace on the layer of the circuit board, wherein the second trace connects the second tap to the rectifier; 
 a third coil including one or more turns of trace on the layer of the circuit board, adjacent to the second trace; 
 a fourth coil including one or more turns of trace on the layer of the circuit board, adjacent to the first trace, on an opposite side of the first trace from the first coil; and 
 a fifth coil including one or more turns of trace on the layer of the circuit board, adjacent to the second trace, on an opposite side of the second trace from the third coil, wherein the fifth coil is connected in series with the fourth coil, the third coil, and the first coil between terminals of the measurement circuit. 
 
     
     
       9. The power converter of  claim 1 , comprising:
 a second trace on the layer of the circuit board, wherein the second trace connects the second tap to the rectifier, wherein the first coil is adjacent to the second trace. 
 
     
     
       10. The power converter of  claim 1 , comprising:
 a second trace on the layer of the circuit board, wherein the second trace connects the second tap to the rectifier, wherein the first coil is adjacent to the second trace; 
 a third coil including one or more turns of trace on the layer of the circuit board, adjacent to the first trace, on an opposite side of the first trace from the first coil; and 
 a fourth coil including one or more turns of trace on the layer of the circuit board, adjacent to the second trace, on an opposite side of the second trace from the first coil, wherein the fourth coil is connected in series with the third coil and the first coil between terminals of the measurement circuit. 
 
     
     
       11. The power converter of  claim 1 , comprising:
 a second trace on an additional layer of the circuit board, stacked vertically with the first trace, wherein the second trace connects the second tap to the rectifier; and 
 a third coil including one or more turns of trace on the additional layer of the circuit board, stacked vertically with the first coil, wherein the first coil and the third coil have opposite winding directions, and wherein the third coil is connected in series with the first coil between terminals of the measurement circuit. 
 
     
     
       12. The power converter of  claim 1 , comprising:
 a comparator circuit configured to detect, based on an estimate of current from the measurement circuit, whether current flowing in the first trace is outside of a range, and, responsive to detection of current outside of the range, generate a signal to cause a circuit connected to the transformer to be opened to stop current from flowing in the transformer. 
 
     
     
       13. The power converter of  claim 1 , comprising:
 a peak detection circuit configured to generate an estimate of peak current in the first trace based on estimates of current from the measurement circuit; and 
 a valley detection circuit configured to generate an estimate of valley current in the first trace based on estimates of current from the measurement circuit. 
 
     
     
       14. The power converter of  claim 13 , comprising a processor configured to:
 receive the estimate of peak current from the peak detection circuit; 
 receive the estimate of valley current from the valley detection circuit; and 
 determine a prediction of a current in the rectifier based on the estimate of peak current and the estimate of valley current. 
 
     
     
       15. The power converter of  claim 1 , wherein the measurement circuit comprises:
 an integrator circuit configured to estimate current flowing in the first trace based on integration over time of voltage across the first coil. 
 
     
     
       16. A system comprising:
 a transformer including a winding that connects a first tap and a second tap; 
 a circuit board; 
 a first trace on a layer of the circuit board, wherein the first trace connects [he] the first tap to a rectifier; 
 a first coil including one or more turns of trace on the layer of the circuit board, positioned to inductively couple to the first trace, wherein the first coil is isolated from the transformer; 
 a second coil including one or more turns of trace on an additional layer of the circuit board, stacked vertically with the first coil; and 
 a measurement circuit, configured to estimate current flowing in the first trace based on voltage across the first coil, wherein the second coil is connected in series with the first coil between terminals of the measurement circuit. 
 
     
     
       17. The system of  claim 16 , comprising:
 a comparator circuit configured to detect, based on an estimate of current from the measurement circuit, whether current flowing in the first trace is outside of a range, and, responsive to detection of current outside of the range, generate a signal to cause a circuit connected to the transformer to be opened to stop current from flowing in the transformer. 
 
     
     
       18. The power converter of  claim 16 , comprising:
 a third coil including one or more turns of trace on the layer of the circuit board, adjacent to the first trace, on a same side of the first trace as the first coil, wherein the third coil is connected in series with the first coil between terminals of the measurement circuit. 
 
     
     
       19. A system comprising:
 a transformer including a secondary winding that connects a first tap and a second tap; 
 a first length of conductor that connects the first tap to a rectifier; 
 a coil including two or more turns of conductor in a spiral arrangement that is coplanar with the first length of conductor, and adjacent to the first length of conductor, wherein the coil is isolated from the transformer; and 
 a measurement circuit configured to estimate current flowing in the first length of conductor based on voltage across the coil. 
 
     
     
       20. The system of  claim 19 , comprising:
 a comparator circuit configured to detect, based on an estimate of current from the measurement circuit, whether current flowing in the first length of conductor is outside of a range, and, responsive to detection of current outside of the range, generate a signal to cause a circuit connected to the transformer to be opened to stop current from flowing in the transformer.

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This application claims the benefit of U.S. Provisional Application No. 62/785,776, filed on Dec. 28, 2018. The content of the foregoing application is incorporated herein by reference in its entirety for all purposes. 
    
    
     TECHNICAL FIELD 
     This disclosure relates to current sensors for power converters. 
     BACKGROUND 
     Power converters are used to transfer power between circuits operating at different voltage levels. For example, power converters may be employed at terminals of high voltage power transmission lines. For example, power converters may be employed in power supplies for computing server racks. Power converters may include components or devices that are only rated to operate well or safely in a particular range of voltages and/or currents. Current sensors may be used in power converters to detect fault conditions and/or to provide feedback for control of a power converter. Examples of current sensors that may be used to measure currents in a power converter include a current transformer, a current shunt with an isolation amplifier, or a Hall Effect integrated circuit. 
     SUMMARY 
     Disclosed herein are implementations of current sensors for power converters. 
     In a first aspect, the subject matter described in this specification can be embodied in systems that include a transformer including a winding that connects a first tap and a second tap; a circuit board; a first trace on a layer of the circuit board, wherein the first trace connects the first tap to a rectifier; a coil including one or more turns of trace on the layer of the circuit board, adjacent to the first trace; and a measurement circuit configured to estimate current flowing in the first trace based on of voltage across the coil. 
     In a second aspect, the subject matter described in this specification can be embodied in systems that include a circuit board; a first trace on a layer of the circuit board; a coil including one or more turns of trace on the layer of the circuit board, adjacent to the first trace; and a measurement circuit, configured to estimate current flowing in the first trace based on voltage across the coil. 
     In a third aspect, the subject matter described in this specification can be embodied in systems that include a transformer including a winding that connects a first tap and a second tap; a circuit board; a first trace on a layer of the circuit board, wherein the first trace connects to the first tap to a rectifier; a coil including one or more turns of trace on the layer of the circuit board, positioned to inductively couple to the first trace; and a measurement circuit, configured to estimate current flowing in the first trace based on voltage across the coil. 
     In a fourth aspect, the subject matter described in this specification can be embodied in systems that include a transformer including a secondary winding that connects a first tap and a second tap; a first length of conductor that connects the first tap to a rectifier; a coil including two or more turns of conductor in a spiral arrangement that is coplanar with the first length of conductor, and adjacent to the first length of conductor; and a measurement circuit configured to estimate current flowing in the first length of conductor based on voltage across the coil. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The disclosure is best understood from the following detailed description when read in conjunction with the accompanying drawings. It is emphasized that, according to common practice, the various features of the drawings are not to-scale. On the contrary, the dimensions of the various features are arbitrarily expanded or reduced for clarity. 
         FIG.  1    is a circuit diagram of an example of a system including a high voltage to low voltage DC/DC converter with a current sensor. 
         FIG.  2    is a circuit diagram of an example of a system including a power converter with a coil for sensing current. 
         FIG.  3    is a circuit diagram of an example of a system including a power converter with a pair of coils in series for sensing current. 
         FIG.  4    is a circuit diagram of an example of a system including a power converter with multiple coils in series for sensing current. 
         FIG.  5    is an illustration of an example of a system including a two-layer circuit board with a coil for sensing current. 
         FIG.  6    is an illustration of an example of a system including a four-layer circuit board with a stack of coils in series for sensing current. 
         FIG.  7    is an illustration of an example of a system including an eight-layer circuit board with a stack of coils in series for sensing current. 
         FIG.  8    is an illustration of an example of a system including an eight-layer circuit board with a stack of coils in series for sensing current. 
         FIG.  9    is a circuit diagram of an example of a system including a current sensor. 
         FIG.  10    is a circuit diagram of an example of a system including a current sensor. 
         FIG.  11    is a circuit diagram of an example of a system including a power converter with a coil for sensing current. 
         FIG.  12    is a circuit diagram of an example of a system including a power converter with three coils in series for sensing current. 
         FIG.  13    is a circuit diagram of an example of a system including a power converter with a stack of interleaved conductors on multiple layers of a circuit board and a stack of coils with alternating winding directions for sensing current in the interleaved conductors. 
         FIG.  14    is an illustration of an example of a system including a two-layer circuit board with a stack of coils in series with alternating winding directions for sensing current. 
         FIG.  15    is an illustration of an example of a system including a four-layer circuit board with a stack of coils in series with alternating winding directions for sensing current. 
         FIG.  16    is a circuit diagram of an example of a system including a power converter with a stack of interleaved conductors on multiple layers of a circuit board and one or more coils with interlayer turns for sensing current in the interleaved conductors. 
         FIG.  17    is an illustration of an example of a system including a four-layer circuit board with two coils with interlayer turns for sensing current. 
         FIG.  18    is an illustration of an example of a system including a four-layer circuit board with two horizontal stacks of coils with interlayer turns for sensing current. 
     
    
    
     DETAILED DESCRIPTION 
     Described herein are systems, circuits, and methods that may be used to measure current in power converters. In isolated power converters, measurement of the high-frequency transformer current can be used for high-speed fault management and feedback for high-bandwidth controls. As switching frequencies of power converters are being pushed greater than 1 MHz (e.g., facilitated by the use of GaN switches), conventional isolated current sensors may fail to address this need. A current sensor for fault detection that is fast (e.g., &lt;1 ns), high bandwidth (e.g., &gt;10 MHz), isolated, compact, have a capability to sense a wide range of current (e.g., including currents greater than 200 A) is desirable. It is noted that in some power converters, current sensing is preferred on the low voltage side because the low voltage side may be susceptible to transformer saturation in absence of blocking capacitor, and higher current (e.g., ˜200 Amperes) on the low voltage side may enable better resolution of current measurements. 
     A time varying current through a conductor induces a magnetic field. If a coil is placed near this varying magnetic field, a voltage is induced, according to Faradays law. This voltage can be integrated to result in a parameter (e.g., a voltage) proportionate to current flowing in the conductor. For example, a printed circuit board (PCB) embedded current sensor may be used to sense current in a power converter. One or more PCB embedded coils may be built near transformer current planes, and these PCB embedded coils would be induced with a voltage due to the varying magnetic fields. A measurement circuit with a proper filter signal conditioner may be connected to the one or more PCB embedded coils to extract the current flowing through the transformer. A current sensors using one or more PCB embedded coils and a measurement circuit may offer advantages, such as, being isolated since it does not make any contact with the high current terminals; low cost for coil as it may be constructed of traces embedded in the PCB; high-speed and high bandwidth; low or negligible delay; and/or minimal analog circuitry required (e.g., an integrator circuit and some filtering). The overall sensor cost may be favorable compared with previous solutions. 
     The current sensors described herein may provide advantages over some conventional current sensing techniques. For example, a current transformer may not be able to handle high current measurements (e.g., &gt;20 Amperes), which means the current transformer may only be available for use on the high voltage side of a DC/DC converter, and available parts may not meet hipot rating and creep age requirements. The bandwidth of a current transformer may be substantially lower than the disclosed current sensors. For example, a current transformer may be limited to an approximately 500 kHz bandwidth, while the some of the disclosed current sensors may support bandwidths greater than 10 MHz. A current transformer may also have additional large components that result in higher cost and volume and/or lower reliability than some of the disclosed current sensors. 
     For example, a current shunt with operational amplifier includes a resistor in the power converter circuit that may generate significant loss in efficiency of the power converter. The bandwidth of the current shunt sensor may be significantly limited by the isolation amplifier relative to some of the disclosed current sensors. Greater delay may be introduced by the isolation amplifier relative to some of the disclosed current sensors. The isolation amplifier has to be powered with an isolated power supply, which may consume more power and/or take up more space than some of the disclosed current sensors. A current shunt with operational amplifier may also have additional large components that result in higher cost and volume and/or lower reliability than some of the disclosed current sensors. 
     For example, a Hall Effect integrated circuit may substantially lower bandwidth (e.g., typical off-the shelf Hall Effect integrated circuits have bandwidth on the order of 100 kHz) than some of the disclosed current sensors. Greater delay may be introduced by the isolation stage used with a Hall Effect integrated circuit relative to some of the disclosed current sensors. Some of the disclosed current sensors may have greater accuracy over temperature and lifetime than a current sensor using a Hall Effect integrated circuit. Some of the disclosed current sensors may have more linearity than a current sensor using a Hall Effect integrated circuit. A Hall Effect integrated circuit based current sensor may also have additional large components that result in higher cost and volume and/or lower reliability than some of the disclosed current sensors. 
     While the disclosure has been described in connection with certain embodiments, it is to be understood that the disclosure is not to be limited to the disclosed embodiments but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the scope of the appended claims, which scope is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures. 
       FIG.  1    is a circuit diagram of an example of a system  100  including a high voltage to low voltage DC/DC converter with a current sensor. The system  100  includes a power converter; including a transformer  110 , an inverter  120 , and a rectifier  130 ; which transfer power between a high voltage battery  140  (e.g., a 400-volt or an 800-volt battery) and a low voltage battery  142  (e.g., a 12-volt or a 48-volt battery). The high voltage battery  140  is connected to terminals of the inverter  120  and the low voltage battery  142  is connected to terminals of the rectifier  130 . The system also includes a current sensor, including a coil  150  connected to a measurement circuit  160  and positioned for measuring current flowing between the transformer  110  and the rectifier  130 . The current sensor may be used for measurement of the high-frequency currents through the transformer  110  that can be used for high-speed fault management and feedback for high-bandwidth controls. 
     The system  100  includes a transformer  110  that couples power from an inverter  120  to a rectifier  130 . The transformer includes a winding  112  (e.g., a secondary winding) that connects a first tap and a second tap. 
     The system  100  includes a first length of conductor  170  that connects the first tap to the rectifier  130 . Alternating current from the transformer  110  may flow through the first length of conductor  170 . For example, the first length of conductor  170  may include a wire (e.g., 18 gauge copper wire), which may be wrapped in insulation. In some implementations, the system includes a circuit board (e.g., a PCB) and the first length of conductor  170  is a first trace on a layer of the circuit board, wherein the first trace connects the first tap to the rectifier  130 . For example, the layer of the circuit board may be a conductive layer (e.g., a copper layer) of a circuit board (e.g., a printed circuit board (PCB)) that includes a stack of substrate layers, which may be laminated together to form the circuit board. 
     The system  100  includes a coil  150  including two or more turns of conductor in a spiral arrangement that is coplanar with the first length of conductor  170 , and adjacent to the first length of conductor  170 . The coil  150  is adjacent to the first length of conductor  170  in the sense that there are no conductors positioned in the space directly between the coil  150  and the first length of conductor  170 . For example, the coil  150  may include wire formed into a spiral that is positioned (e.g., by soldering or another fastening structure) to be coplanar with the first length of conductor  170 . In some implementations, the system includes a circuit board (e.g., a PCB) and the coil  150  includes one or more turns of trace on the layer of the circuit board, adjacent to the first trace. The coil  150  is adjacent to the first trace in the sense that there are no conductors positioned in the space directly between the coil  150  and the first trace. 
     For example, the coil  150  (e.g., including one or more turns of trace on the layer of a circuit board and/or two or more turns of conductor in a spiral arrangement that is coplanar with the first length of conductor  170 ) may be positioned to inductively couple to the first length of conductor  170  (e.g., the first trace). In some implementations, an edge of the coil  150  is within one millimeter of an edge of the first length of conductor  170  (e.g., the first trace). 
     The system  100  includes a measurement circuit  160  configured to estimate current flowing in the first length of conductor  170  based on voltage across the coil  150 . For example, the measurement circuit  160  may include an integrator circuit that is configured to estimate current flowing in the first length of conductor  170  based on integration over time of voltage across the coil  150 . A time varying current through the first length of conductor  170  induces a magnetic field. According to Faradays Law, this varying magnetic field induces a voltage in the coil  150 . This voltage across the coil  150  can be integrated to result in a parameter (e.g., a voltage) proportionate to current flowing in the first length of conductor  170  (e.g., the first trace). In some implementations, the measurement circuit  160  may be connected to a series of coils positioned near the current flowing in the first length of conductor  170  and the voltages across the series of coils may be integrated to estimate this current. For example, a series of coils may be arranged as depicted in  FIG.  3   ,  FIG.  4   ,  FIG.  6   ,  FIG.  7   , and/or  FIG.  8   . For example, the measurement circuit  160  may include a resistor-capacitor network (an RC network) that integrates the voltages by storing charge on one or more capacitors. In some implementations, the measurement circuit  160  includes components for signal conditioning that converts a parameter (e.g., a voltage) proportional to the current flowing in the first length of conductor  170  to a format that may be readily read or utilized by another circuitry, such as, a processor or microcontroller that controls the inverter  120  and/or the rectifier  130  or a transformer protection circuit that is configured to protect the transformer  110  in the event of a fault condition. For example, the measurement circuit  160  may include an operational amplifier with additional components configured to amplify the result of an integration of voltage across the coil  150  into a useful format or range. For example, the measurement circuit  160  may be implemented as described in relation to  FIG.  10   . 
     The rectifier  130  may be suitable to be interfaced with the low voltage battery  142  and be able to provide high efficiency while meeting desired specifications. Switching control may be formulated for operation of a topology of the inverter  120  and the rectifier  130  to attain zero voltage switching over an entire battery range. For example, a processor (e.g., a microprocessor or a microcontroller) may be used to implement switching control for the system  100 . Zero voltage switching enables use of switching frequency in the MHz range and may reduce the size of magnetic components. This may result in obtaining high power density, which converts to savings in volume and weight of the system  100 . 
     For example, for high voltage batteries (e.g., an 800-volt battery), newer multilevel topologies may be used to exploit the benefits of latest wide band-gap GaN technology. The inverter  120  may be suitable to be interfaced with the high voltage battery  140  and be able to provide high efficiency while meeting desired specifications. In some implementations, switching control may be formulated to achieve active voltage balancing of split capacitors in the inverter  120 . For example, the inverter  120  may include a three-level stacked half-bridge topology. For example, techniques described herein may be implemented for power converters fabricated with other technologies, such as Si technology. For example, techniques described herein may be implemented for power converters connected to various types of batteries with various voltage levels. 
     The converters of the system  100  may be bidirectional in the sense that power may be transferred from the high voltage battery  140  to the low voltage battery  142  at one time as well as from the low voltage battery  142  to the high voltage battery  140  at another time. The bidirectional nature of the inverter  120  and the rectifier  130  may facilitate the use of system  100  in applications of high voltage to low voltage DC/DC converters, and high voltage chargers. 
     In the example of  FIG.  1   , the first length of conductor  170  that bears the measured current connects the winding  112  of the transformer  110  to the rectifier  130 . In some implementations (not shown in  FIG.  1   ), the current sensor, including the coil  150 , may be positioned to measure current in a length of conductor (e.g., a trace on a circuit board) that connects a winding (e.g., a primary winding) of the transformer  110  to the inverter  120 . 
       FIG.  2    is a circuit diagram of an example of a system  200  including a power converter with a coil for sensing current. In this example, a one-coil solution is positioned near a trace connected to a transformer, which may be used for transformer current measurement. The system  200  includes a transformer  210  and a rectifier  220 . The rectifier  220  may be implemented on a circuit board (e.g., a PCB). The system  200  includes a first trace  240  on a layer of the circuit board that connects the transformer  210  to the rectifier  220 . The system  200  includes a second trace  242  on the layer of the circuit board that connects the transformer  210  to the rectifier  220 . The system  200  includes a coil  250  including one or more turns of trace on the layer of the circuit board, adjacent to the first trace  240 . The coil  250  may be used with a measurement circuit (e.g., the measurement circuit  160 ) (not shown in  FIG.  2   ) to measure a current flowing through the first trace  240 . 
     The transformer  210  includes a primary winding  212  and a secondary winding  214 . The secondary winding  214  connects a first tap  216  and a second tap  218  of the transformer  210 . 
     The rectifier  220  includes a first switch  222 , a second switch  224 , and a first capacitor  230  in a full-bridge topology. The rectifier  220  includes a first switch  226 , a second switch  228 , and a second capacitor  232  in a full-bridge topology. Although not explicitly shown in  FIG.  2   , a load (e.g., the low voltage battery  142 ) may be connected across output terminals of the rectifier  220 . For example, the first capacitor  230  and the second capacitor  232  may be connected in parallel between the output terminals of the rectifier  220 . 
     The system  200  includes a first trace  240  on a layer of the circuit board. The first trace  240  connects to the first tap  216  to the rectifier  220 . The system  200  includes a second trace  242  on the layer of the circuit board. The second trace  242  connects to the second tap  218  to the rectifier  220 . For example, the second trace  242  may be connected in series with the first trace  240 , such that the same current flows through the first trace  240  and the second trace  242 . For example, the first trace  240  and the second trace  242  may be copper traces on a PCB. 
     The system  200  includes a coil  250  including one or more turns of trace on the layer of the circuit board, adjacent to the first trace  240 . The coil  250  may be positioned to inductively couple to the first trace  240 . For example, an edge of the coil  250  may be within one millimeter of an edge of the first trace  240 . In some implementations, the coil  250  includes two or more turns (e.g., four turns) arranged in a spiral. Terminals of the coil  250  may be connected to a measurement circuit (e.g., the measurement circuit  160 ) (not shown in  FIG.  2   ) to measure a current flowing through the first trace  240 . For example, an output (e.g., a voltage) of the measurement circuit may be proportional to a current (I) flowing in the first trace  240  in a format that may be read and/or utilized by other circuitry, such as, a processor or microcontroller that controls an inverter and/or the rectifier  220  or a transformer protection circuit that is configured to protect the transformer  210  in the event of a fault condition. 
     In some implementations (e.g., as shown in  FIGS.  2 - 3   ), multiple coils may be connected in series to capture more flux and induce more voltage. Another motivation to use multiple coils is for canceling stray flux. In some implementations, the primary side of system  200  includes a high voltage power source exceeding 110V, 240V, 277V, 400V, 800V, and so forth. In some implementations, the secondary side of system  200  produces an out of relatively lower voltage, such as 48V, 24V, 20V, 12V, 9V, 5V, and so forth. 
       FIG.  3    is a circuit diagram of an example of a system  300  including a power converter with a pair of coils ( 350  and  360 ) in series for sensing current. Dual coils may be positioned near a trace connected to a tap of the transformer  210 . The two coils may be in anti-winding direction (e.g., if one is wound clockwise, the other should be wound anti-clockwise to induce voltage in same direction). The system  300  includes the transformer  210  and a rectifier  220  of  FIG.  2   , connected by the first trace  240  and the second trace  242 . The system  300  includes a first coil  350  including one or more turns of trace on the layer of the circuit board, adjacent to the first trace  240 . The system  300  includes a second coil  360  including one or more turns of trace on the layer of the circuit board, adjacent to the first trace  240 , on an opposite side of the first trace  240  from the first coil  350 . The second coil  360  is connected in series with the first coil  350  between terminals of a measurement circuit (e.g., the measurement circuit  160 ) (not shown in  FIG.  3   ). 
     The system  300  includes a first coil  350  including one or more turns of trace on the layer of the circuit board, adjacent to the first trace  240 . The first coil  350  may be positioned to inductively couple to the first trace  240 . For example, an edge of the first coil  350  may be within one millimeter of an edge of the first trace  240 . In some implementations, the first coil  350  includes two or more turns (e.g., four turns) arranged in a spiral. 
     The system  300  includes a second coil  360  including one or more turns of trace on the layer of the circuit board, adjacent to the first trace  240 , on an opposite side of the first trace  240  from the first coil  350 . For example, the second coil  360  may be positioned to inductively couple to the first trace  240 . For example, the first coil  350  and the second coil  360  may have opposite winding directions. 
     The second coil  360  is connected in series with the first coil  350  between terminals of a measurement circuit (e.g., the measurement circuit  160 ) (not shown in  FIG.  2   ) to measure a current flowing through the first trace  240 . For example, an output (e.g., a voltage) of the measurement circuit may be proportional to a current (I) flowing in the first trace  240  in a format that may be read and/or utilized by other circuitry, such as, a processor or microcontroller that controls an inverter and/or the rectifier  220  or a transformer protection circuit that is configured to protect the transformer  210  in the event of a fault condition. 
     In some implementations (not shown in  FIG.  3   ), a pair of coils may be positioned coplanar with a first length of conductor (e.g., a wire or a trace) bearing current from the transformer  210  and on opposite sides of the first length of conductor. Thus, the pair of coils do not necessarily need to be implemented on a circuit board with traces. Such a system may include a first coil including two or more turns of conductor in a spiral arrangement that is coplanar with the first length of conductor, and adjacent to the first length of conductor. This system may include a second coil including two or more turns of conductor in a spiral arrangement that is coplanar with the first length of conductor, adjacent to the first length of conductor, on an opposite side of the first length of conductor from the first coil. The second coil may be connected in series with the first coil between terminals of a measurement circuit (e.g., the measurement circuit  160 ). 
       FIG.  4    is a circuit diagram of an example of a system  400  including a power converter with multiple coils in series for sensing current. In this example, four coils are positioned on both sides of two traces respectively connected to two taps of the transformer  210  that both bear a current through a winding of the transformer  210 . Alternate coils may be wound 180 degrees out of phase. The system  400  includes the transformer  210  and a rectifier  220  of  FIG.  2   , connected by the first trace  240  and the second trace  242 . The system  400  includes a first coil  450  including one or more turns of trace on the layer of the circuit board, adjacent to the first trace  240 . The system  400  includes a second coil  470  including one or more turns of trace on the layer of the circuit board, adjacent to the second trace  242 . The system  400  includes a third coil  460  including one or more turns of trace on the layer of the circuit board, adjacent to the first trace  240 , on an opposite side of the first trace  240  from the first coil  450 . The system  400  includes a fourth coil  480  including one or more turns of trace on the layer of the circuit board, adjacent to the second trace  242 , on an opposite side of the second trace  242  from the second coil  470 . The second coil  470  is connected in series with the first coil  450  between terminals of a measurement circuit (e.g., the measurement circuit  160 ) (not shown in  FIG.  4   ). The fourth coil  480  is connected in series with the third coil  460 , the second coil  470 , and the first coil  450  between terminals of the measurement circuit. 
     The system  400  includes a first coil  450  including one or more turns of trace on the layer of the circuit board, adjacent to the first trace  240 . The first coil  450  may be positioned to inductively couple to the first trace  240 . For example, an edge of the first coil  450  may be within one millimeter of an edge of the first trace  240 . In some implementations, the first coil  450  includes two or more turns (e.g., four turns) arranged in a spiral. 
     The system  400  includes a second coil  470  including one or more turns of trace on the layer of the circuit board, adjacent to the second trace  242 . The second coil  470  may be positioned to inductively couple to the second trace  242 . For example, an edge of the second coil  470  may be within one millimeter of an edge of the second trace  242 . In some implementations, the second coil  470  includes two or more turns (e.g., four turns) arranged in a spiral. 
     The system  400  includes a third coil  460  including one or more turns of trace on the layer of the circuit board, adjacent to the first trace  240 , on an opposite side of the first trace  240  from the first coil  450 . For example, the third coil  460  may be positioned to inductively couple to the first trace  240 . For example, the first coil  450  and the third coil  460  may have opposite winding directions. 
     The system  400  includes a fourth coil  480  including one or more turns of trace on the layer of the circuit board, adjacent to the second trace  242 , on an opposite side of the second trace  242  from the second coil  470 . For example, the fourth coil  480  may be positioned to inductively couple to the second trace  242 . For example, the second coil  470  and the fourth coil  480  may have opposite winding directions. 
     The second coil  470  is connected in series with the first coil  450  between terminals of a measurement circuit (e.g., the measurement circuit  160 ) (not shown in  FIG.  4   ) to measure a current flowing through the first trace  240  and the second trace  242 . The fourth coil  480  is connected in series with the third coil  460 , the second coil  470 , and the first coil  450  between terminals of the measurement circuit. For example, the second coil  470  and the first coil  450  may be wound in opposite direction (e.g., 180 degrees out of phase). For example, an output (e.g., a voltage) of the measurement circuit may be proportional to a current (I) flowing in the first trace  240  and the second trace  242  in a format that may be read and/or utilized by other circuitry, such as, a processor or microcontroller that controls an inverter and/or the rectifier  220  or a transformer protection circuit that is configured to protect the transformer  210  in the event of a fault condition. 
     In some implementations (not shown in  FIG.  4   ), four coils may be positioned on both sides of two traces respectively connected to two taps of the transformer  210  that both bear a current through a winding of the transformer  210 . The four coils may be coplanar with their respective current bearing lengths of conductor. Thus, the set of four coils do not necessarily need to be implemented on a circuit board with traces. Such a system may include a first coil including two or more turns of conductor in a spiral arrangement that is coplanar with the first length of conductor, and adjacent to the first length of conductor. This system may include a second coil including two or more turns of conductor in a spiral arrangement that is coplanar with the second length of conductor, adjacent to the second length of conductor. This system may include a third coil including two or more turns of conductor in a spiral arrangement that is coplanar with the first length of conductor, adjacent to the first length of conductor, on an opposite side of the first length of conductor from the first coil. This system may include a fourth coil including two or more turns of conductor in a spiral arrangement that is coplanar with the second length of conductor, adjacent to the second length of conductor, on an opposite side of the second length of conductor from the second coil. The second coil may be connected in series with the first coil between terminals of a measurement circuit (e.g., the measurement circuit  160 ). The fourth coil may be connected in series with the third coil, the second coil, and the first coil between terminals of the measurement circuit. 
     In some implementations (not shown in  FIG.  4   ), two coils are both positioned coplanar with a first length of conductor (e.g., a wire or a trace on a circuit board), along a same side of the first length of conductor, and adjacent to the first length of conductor. For example, a system may include a first coil including two or more turns of conductor in a spiral arrangement that is coplanar with the first length of conductor, and adjacent to the first length of conductor. The system may also include a second coil including two or more turns of conductor in a spiral arrangement that is coplanar with a first length of conductor, adjacent to the first length of conductor, on a same side of the first length of conductor as the first coil. The second coil may be connected in series with the first coil between terminals of a measurement circuit (e.g., the measurement circuit  160 ). 
     For example, where the first length of conductor is first trace on a layer of a circuit board, a system may include a first coil including one or more turns of trace on the layer of the circuit board, adjacent to the first trace. The system may also include a second coil including one or more turns of trace on the layer of the circuit board, adjacent to the first trace, on a same side of the first trace as the first coil. The second coil may be connected in series with the first coil between terminals of a measurement circuit (e.g., the measurement circuit  160 ). 
     For example, where the first length of conductor is first trace on a layer of a circuit board, a system may include a first coil including one or more turns of trace on the layer of the circuit board, positioned to inductively couple to the first trace. The system may also include a second coil including one or more turns of trace on the layer of the circuit board, positioned to inductively couple to the first trace, on a same side of the first trace as the first coil. The second coil may be connected in series with the first coil between terminals of a measurement circuit (e.g., the measurement circuit  160 ). 
       FIG.  5    is an illustration of an example of a system  500  including a two-layer circuit board with a coil for sensing current. The system  500  includes a two-layer circuit board (e.g., a PCB) that includes a top layer  510  and a bottom layer  512 . The system  500  includes a coil  520  that includes turns of trace (e.g., copper trace) on the top layer  510  of the circuit board. The coil  520  is connected to a first terminal  540  on the bottom layer  512  by a first via  560 . The coil  520  is connected to a second terminal  542  on the bottom layer  512  by a second via  562 . The coil  520  includes a first turn  530 , a second turn  532 , a third turn  534 , and a fourth turn  536  that spiral successively inward on the top layer  510 , from the first via  560  to the second via  562 . For example, the coil  520  may be used to implement a coil of the system  100  of  FIG.  1   , of the system  200  of  FIG.  2   , of the system  300  of  FIG.  3   , or of the system  400  of  FIG.  4   . 
       FIG.  6    is an illustration of an example of a system  600  including a four-layer circuit board with a stack of coils in series for sensing current. The system  600  includes a four-layer circuit board (e.g., a PCB) that includes a first layer  610  (e.g., a top layer), a second layer  612  (e.g., a hidden layer), a third layer  614  (e.g., a hidden layer), and a fourth layer  616  (e.g., a bottom layer). The system  600  includes a stack of coils  620  that each include one or more turns of trace (e.g., copper trace) on a respective layer of the circuit board. The stack of coils  620  is connected in series by vias ( 660 ,  662 , and  664 ). The stack of coils  620  is connected to a first terminal  640  on the first layer  610 . The stack of coils  620  is connected to a second terminal  642  on the fourth layer  616 . For example, the coils ( 630 ,  632 ,  634 , and  636 ) of the stack of coils  620  may have the same winding direction. For example, the stack of coils  620  may be used to implement a current sensor the system  100  of  FIG.  1   , of the system  200  of  FIG.  2   , of the system  300  of  FIG.  3   , or of the system  400  of  FIG.  4   . 
     The system  600  includes a first coil  630  on the first layer  610 . Although not shown in  FIG.  6   , the first layer  610  may also include a first trace (e.g., the first length of conductor  170  or the first trace  240 ) that is adjacent to and/or inductively coupled to the first coil  630 . This first trace may bear a time varying current that is measured using a current sensor that includes the stack of coils  620  (e.g., as described in relation to  FIG.  1   ). The system includes a second coil  632  including one or more turns of trace on an additional layer (i.e., the second layer  612 ) of the circuit board, stacked vertically with the first coil  630 . The second coil  632  is connected in series with the first coil  630  between terminals (e.g., the first terminal  640  and the second terminal  642 ) of a measurement circuit (e.g., the measurement circuit  160 ) (not shown in  FIG.  6   ). The second coil  632  is connected to the first coil  630  by the via  660 . The system includes a third coil  634  including one or more turns of trace on an additional layer (i.e., the third layer  614 ) of the circuit board, stacked vertically with the first coil  630 . The third coil  634  is connected in series with the first coil  630  between terminals (e.g., the first terminal  640  and the second terminal  642 ) of a measurement circuit. The third coil  634  is connected to the second coil  632  by the via  662 . The system includes a fourth coil  636  including one or more turns of trace on an additional layer (i.e., the fourth layer  616 ) of the circuit board, stacked vertically with the first coil  630 . The fourth coil  636  is connected in series with the first coil  630  between terminals (e.g., the first terminal  640  and the second terminal  642 ) of a measurement circuit. The fourth coil  636  is connected to the third coil  634  by the via  664 . 
       FIG.  7    is an illustration of an example of a system  700  including an eight-layer circuit board with a stack of coils in series for sensing current. The system  700  includes an eight-layer circuit board (e.g., a PCB) that includes a first layer  710  (e.g., a top layer), a second layer  711  (e.g., a hidden layer), a third layer  712  (e.g., a hidden layer), a fourth layer  713  (e.g., a hidden layer), a fifth layer  714  (e.g., a hidden layer), a sixth layer  715  (e.g., a hidden layer), a seventh layer  716  (e.g., a hidden layer), and an eighth layer  717  (e.g., a bottom layer). The system  700  includes a stack of coils  720  that each include one or more turns of trace (e.g., copper trace) on a respective layer of the circuit board. The stack of coils  720  is connected in series by vias. The stack of coils  720  is connected to a first terminal  740  on the first layer  710 . The stack of coils  720  is connected to a second terminal  742  on the eighth layer  717 . For example, the coils ( 730 ,  731 ,  732 ,  733 ,  734 ,  735 ,  736 , and  737 ) of the stack of coils  720  may have the same winding direction. For example, the stack of coils  720  may be used to implement a current sensor the system  100  of  FIG.  1   , of the system  200  of  FIG.  2   , of the system  300  of  FIG.  3   , or of the system  400  of  FIG.  4   . 
     The system  700  includes a first coil  730  on the first layer  710 . Although not shown in  FIG.  7   , the first layer  710  may also include a first trace (e.g., the first length of conductor  170  or the first trace  240 ) that is adjacent to and/or inductively coupled to the first coil  730 . This first trace may bear a time varying current that is measured using a current sensor that includes the stack of coils  720  (e.g., as described in relation to  FIG.  1   ). The system includes a second coil  731  including one or more turns of trace on an additional layer (i.e., the second layer  711 ) of the circuit board, stacked vertically with the first coil  730 . The second coil  731  is connected in series with the first coil  730  between terminals (e.g., the first terminal  740  and the second terminal  742 ) of a measurement circuit (e.g., the measurement circuit  160 ) (not shown in  FIG.  7   ). The second coil  731  is connected to the first coil  730  by a via. The system includes a third coil  732  including one or more turns of trace on an additional layer (i.e., the third layer  712 ) of the circuit board, stacked vertically with the first coil  730 . The third coil  732  is connected in series with the first coil  730  between terminals (e.g., the first terminal  740  and the second terminal  742 ) of a measurement circuit. The third coil  732  is connected to the second coil  731  by a via. The system includes a fourth coil  733  including one or more turns of trace on an additional layer (i.e., the fourth layer  713 ) of the circuit board, stacked vertically with the first coil  730 . The fourth coil  733  is connected in series with the first coil  730  between terminals (e.g., the first terminal  740  and the second terminal  742 ) of a measurement circuit. The fourth coil  733  is connected to the third coil  732  by a via. The system includes a fifth coil  734  including one or more turns of trace on an additional layer (i.e., the fifth layer  714 ) of the circuit board, stacked vertically with the first coil  730 . The fifth coil  734  is connected in series with the first coil  730  between terminals (e.g., the first terminal  740  and the second terminal  742 ) of a measurement circuit. The fifth coil  734  is connected to the fourth coil  733  by a via. The system includes a sixth coil  735  including one or more turns of trace on an additional layer (i.e., the sixth layer  715 ) of the circuit board, stacked vertically with the first coil  730 . The sixth coil  735  is connected in series with the first coil  730  between terminals (e.g., the first terminal  740  and the second terminal  742 ) of a measurement circuit. The sixth coil  735  is connected to the fifth coil  734  by a via. The system includes a seventh coil  736  including one or more turns of trace on an additional layer (i.e., the seventh layer  716 ) of the circuit board, stacked vertically with the first coil  730 . The seventh coil  736  is connected in series with the first coil  730  between terminals (e.g., the first terminal  740  and the second terminal  742 ) of a measurement circuit. The seventh coil  736  is connected to the sixth coil  735  by a via. The system includes an eighth coil  737  including one or more turns of trace on an additional layer (i.e., the eighth layer  717 ) of the circuit board, stacked vertically with the first coil  730 . The eighth coil  737  is connected in series with the first coil  730  between terminals (e.g., the first terminal  740  and the second terminal  742 ) of a measurement circuit. The eighth coil  737  is connected to the seventh coil  736  by a via. 
       FIG.  8    is an illustration of an example of a system  800  including an eight-layer circuit board with a stack of coils in series for sensing current. The system  800  includes an eight-layer circuit board (e.g., a PCB) that includes a first layer  810  (e.g., a top layer), a second layer  811  (e.g., a hidden layer), a third layer  812  (e.g., a hidden layer), a fourth layer  813  (e.g., a hidden layer), a fifth layer  814  (e.g., a hidden layer), a sixth layer  815  (e.g., a hidden layer), a seventh layer  816  (e.g., a hidden layer), and an eighth layer  817  (e.g., a bottom layer). The system  800  includes a stack of coils  820  that each include one or more turns of trace (e.g., copper trace) on a respective layer of the circuit board. In this example, the stack of coils  820  includes four coils ( 830 ,  832 ,  834 , and  836 ), each including two turns of trace for a total of eight turns of trace in the stack of coils  820 . The stack of coils  820  is connected in series by vias ( 860 - 865 ). The stack of coils  820  is connected to a first terminal  840  on the first layer  810 . The stack of coils  820  is connected to a second terminal  842  on the eighth layer  817 . For example, the coils of the stack of coils  820  may have the same winding direction. For example, the stack of coils  820  may be used to implement a current sensor the system  100  of  FIG.  1   , of the system  200  of  FIG.  2   , of the system  300  of  FIG.  3   , or of the system  400  of  FIG.  4   . 
     The system  800  includes a first coil  830  on the first layer  810 . The first coil  830  includes a first turn  870  and a second turn  871  that spiral successively inward on the first layer  810 , from the first terminal  840  to the via  860 . Although not shown in  FIG.  8   , the first layer  810  may also include a first trace (e.g., the first length of conductor  170  or the first trace  240 ) that is adjacent to and/or inductively coupled to the first coil  830 . This first trace may bear a time varying current that is measured using a current sensor that includes the stack of coils  820  (e.g., as described in relation to  FIG.  1   ). The system includes a second coil  832  including one or more turns of trace on an additional layer (i.e., the third layer  812 ) of the circuit board, stacked vertically with the first coil  830 . The second coil  832  is connected in series with the first coil  830  between terminals (e.g., the first terminal  840  and the second terminal  842 ) of a measurement circuit (e.g., the measurement circuit  160 ) (not shown in  FIG.  8   ). The second coil  832  is connected to the first coil  830  by the via  860 , an in-out trace  850  on the second layer  811 , and the via  861 . The second coil  832  includes a third turn  872  and a fourth turn  873  that spiral successively inward on the third layer  812 , from the via  861  to the via  862 . The system includes a third coil  834  including one or more turns of trace on an additional layer (i.e., the fifth layer  814 ) of the circuit board, stacked vertically with the first coil  830 . The third coil  834  is connected in series with the first coil  830  between terminals (e.g., the first terminal  840  and the second terminal  842 ) of a measurement circuit. The third coil  834  is connected to the second coil  832  by the via  862 , an in-out trace  852  on the fourth layer  813 , and the via  863 . The third coil  834  includes a fifth turn  874  and a sixth turn  875  that spiral successively inward on the fifth layer  814 , from the via  863  to the via  864 . The system includes a fourth coil  836  including one or more turns of trace on an additional layer (i.e., the seventh layer  816 ) of the circuit board, stacked vertically with the first coil  830 . The fourth coil  836  is connected in series with the first coil  830  between terminals (e.g., the first terminal  840  and the second terminal  842 ) of a measurement circuit. The fourth coil  836  is connected to the third coil  834  by the via  864 , an in-out trace  854  on the sixth layer  815 , and the via  865 . The fourth coil  836  includes a seventh turn  876  and an eighth turn  877  that spiral successively inward on the seventh layer  816 , from the via  865  to the via  866 . The fourth coil  836  is connected to the second terminal  842  by the via  866 . 
       FIG.  9    is a circuit diagram of an example of a system  900  including a current sensor. The system  900  includes a current sensor configured to measure time varying current flowing in the conductor  910  (e.g., a wire or a trace on a circuit board), where the circuit driving the current in the conductor  910  is not shown in  FIG.  9   . For example, the conductor  910  may be the first length of conductor  170  or the first trace  240 . The system  900  includes a set of one or more coils  920  that are in series between a first terminal  921  and a second terminal  922 . The set of one or more coils  920  may be positioned near the conductor  910  to facilitate current sensing. For example, the set of one or more coils  920  may be positioned adjacent to the conductor and/or such that the set of one or more coils  920  are inductively coupled to the conductor  910 . For example, the set of one or more coils  920  may be positioned in relation to the conductor  910  as described in relation to  FIG.  1   ,  FIG.  2   ,  FIG.  3   ,  FIG.  4   ,  FIG.  5   ,  FIG.  6   ,  FIG.  7   , and/or  FIG.  8   . A measurement circuit, including an integrator circuit  930  and a signal conditioning circuit  940 , is connected between the first terminal  921  and the second terminal  922 . The voltage signal  925  across the set of one or more coils  920  are dropped across a resistor  926 . For example, the voltage signal  925  may approximate a square wave. 
     The voltage signal  925  is input to an integrator circuit  930 . A time varying current through the conductor  910  induces a magnetic field. According to Faradays Law, this time varying magnetic field induces a voltage in the set of one or more coils  920 . This voltage across the coil  150  can be integrated to result in a parameter (e.g., a voltage) proportionate to current flowing in the conductor  910 . For example, the integrator circuit  930  may include a resistor-capacitor network (an RC network) that integrates the voltages by storing charge on one or more capacitors. For example, the integrator circuit  930  may be implemented as described in relation to the measurement circuit  1030  of  FIG.  10   . For example, an output signal  935  of the integrator circuit  930  may approximate a triangle wave that is proportional to the current flowing in the conductor  910  with a small phase shift (e.g., less than one nanosecond). 
     The output signal  935  is input to a signal conditioning circuit  940 . For example, the signal conditioning circuit  940  may be configured to perform differential to single-ended signal conversion and/or bias adjustment. In some implementations, the signal conditioning circuit  940  may apply additional filtering to clean up the output signal  935  and suppress noise. The signal conditioning circuit  940  may output a conditioned signal (e.g., a voltage signal) that is an estimate of the current flowing in the conductor  910  with a small phase shift (e.g., less than one nanosecond) in a format that is accessible by additional circuitry for control and/or protection of a power converter that includes the conductor  910 . 
     The system  900  includes a comparator circuit  950  configured to detect, based on an estimate of current from the integrator circuit  930  (e.g., the conditioned signal output by the signal conditioning circuit), whether current flowing in the conductor  910  (e.g., the first length of conductor  170  or the first trace  240 ) is outside of a range (e.g., an expected or safe range of currents for a transformer or other power converter device). The comparator circuit  950  may be configured for protection of a transformer or another device. In some implementations, the comparator circuit  950  is configured to, responsive to detection of current outside of the range, generate a signal to cause a circuit (e.g., the inverter  120  or the rectifier  130 ) connected to a transformer (e.g., the transformer  110 ) to be opened to stop current from flowing in the transformer. For example, the comparator circuit  950  may be configured to protect the transformer  110  in the event of a fault condition. For example, the comparator circuit  950  may be implemented as the comparator circuit  1050  of  FIG.  10   . 
     The system  900  includes and analog-to-digital converter (ADC)  960 . For example, the ADC  960  may be part of an interface to a processor (e.g., a microprocessor or a microcontroller) that is configured to control a power converter that includes the conductor  910 . For example, the conditioned signal (e.g., a voltage signal) that is an estimate of the current flowing in the conductor  910  may be input to the ADC  960  for sampling and quantization to convert the analog signal to a sequence of digital current estimates that can be processed by a digital control system that controls switches in the power converter (e.g., switches in the inverter  120  and/or the rectifier  130 ). 
       FIG.  10    is a circuit diagram of an example of a system  1000  including a current sensor. The system  1000  includes a current sensor configured to measure time varying current flowing in the conductor  1010  (e.g., a wire or a trace on a circuit board), where the circuit driving the current in the conductor  1010  is not shown in  FIG.  10   . For example, the conductor  1010  may be the first length of conductor  170  or the first trace  240 . The system  1000  includes a set of one or more coils  1020  that are in series between a first terminal  1021  and a second terminal  1022 . The set of one or more coils  1020  may be positioned near the conductor  1010  to facilitate current sensing. For example, the set of one or more coils  1020  may be positioned adjacent to the conductor and/or such that the set of one or more coils  1020  are inductively coupled to the conductor  1010 . For example, the set of one or more coils  1020  may be positioned in relation to the conductor  1010  as described in relation to  FIG.  1   ,  FIG.  2   ,  FIG.  3   ,  FIG.  4   ,  FIG.  5   ,  FIG.  6   ,  FIG.  7   , and/or  FIG.  8   . The voltage signal across the set of one or more coils  1020  are dropped across a resistor  1026 . For example, the voltage signal may approximate a square wave. 
     The voltage signal is input to a measurement circuit  1030 . The measurement circuit  1030  configured to combine the functions of the integrator circuit  930  and the signal conditioning circuit  940  of  FIG.  9   . The measurement circuit  1030  includes a resistor-capacitor network (an RC network) that integrates the voltages by storing charge on capacitors. The RC values may depend on cut-off frequency used for the filter design and can vary significantly between different implementations. The measurement circuit  1030  also includes a pair of opposing diodes across the input terminals of the measurement circuit  1030  for surge protection in the current sensor of the system  1000 . For example, the integrator circuit  930  may be configured to perform differential to single-ended signal conversion and/or bias adjustment using an operational amplifier in a closed loop configuration. For example, an output signal of the measurement circuit  1030  may approximate a triangle wave that is proportional to the current flowing in the conductor  1010  with a small phase shift (e.g., less than one nanosecond). For example, an output signal of the measurement circuit  1030  may be a conditioned signal (e.g., a voltage signal) that is an estimate of the current flowing in the conductor  1010  with a small phase shift (e.g., less than 1 nanosecond) in a format that is accessible by additional circuitry for control and/or protection of a power converter that includes the conductor  1010 . 
     The system  1000  includes a comparator circuit  1050  configured to detect, based on an estimate of current from the measurement circuit  1030  (e.g., the conditioned signal output), whether current flowing in the conductor  1010  (e.g., the first length of conductor  170  or the first trace  240 ) is outside of a range (e.g., an expected or safe range of currents for a transformer or other power converter device). The comparator circuit  1050  may be configured for protection of a transformer or another device. In some implementations, the comparator circuit  1050  is configured to, responsive to detection of current outside of the range, generate a signal to cause a circuit (e.g., the inverter  120  or the rectifier  130 ) connected to a transformer (e.g., the transformer  110 ) to be opened to stop current from flowing in the transformer. For example, the comparator circuit  1050  may be configured to protect the transformer  110  in the event of a fault condition. 
     The comparator circuit  1050  includes a first operational amplifier  1052  configured as an open-loop comparator to compare a voltage representing a current estimate of the current flowing in the conductor  1010  to a high voltage corresponding to a first end of the range of safe current values. The comparator circuit  1050  includes a second operational amplifier  1054  configured as an open-loop comparator to compare a voltage representing a current estimate of the current flowing in the conductor  1010  to a low voltage corresponding to a second end of the range of safe current values. The comparator circuit  1050  includes a logical AND gate  1056  configured to combine the outputs of the first operational amplifier  1052  and the second operational amplifier  1054  to generate a signal to cause a circuit (e.g., the inverter  120  or the rectifier  130 ) connected to a transformer (e.g., the transformer  110 ) to be opened to stop current from flowing in the transformer. For example, the output of the logical AND gate  1056  may indicate whether a fault condition has occurred in a power converter including the conductor  1010 . 
     The system  1000  includes and analog-to-digital converter (ADC)  1060 . For example, the ADC  1060  may be part of an interface to a processor (e.g., a microprocessor or a microcontroller) that is configured to control a power converter that includes the conductor  1010 . For example, the conditioned signal (e.g., a voltage signal) that is an estimate of the current flowing in the conductor  1010  may be input to the ADC  1060  for sampling and quantization to convert the analog signal to a sequence of digital current estimates that can be processed by a digital control system that controls switches in the power converter (e.g., switches in the inverter  120  and/or the rectifier  130 ). 
     The system  1000  includes a peak detection circuit  1070  configured to generate an estimate of peak current in the conductor  1010  (e.g., the first length of conductor  170  or the first trace  240 ) based on estimates of current from the measurement circuit  1030 . For example, the peak detection circuit  1070  may include an operational amplifier. The resulting estimate of peak current is input to an ADC  1062 . For example, the ADC  1062  may be part of an interface to a processor (e.g., a microprocessor or a microcontroller) that is configured to control a power converter that includes the conductor  1010 . 
     The system  1000  includes a valley detection circuit  1072  configured to generate an estimate of valley current in the conductor  1010  (e.g., the first length of conductor  170  or the first trace  240 ) based on estimates of current from the measurement circuit  1030 . For example, the valley detection circuit  1072  may include an operational amplifier. The resulting estimate of valley current is input to an ADC  1064 . For example, the ADC  1064  may be part of an interface to a processor (e.g., a microprocessor or a microcontroller) that is configured to control a power converter that includes the conductor  1010 . 
     Although not shown in  FIG.  10   , the system  1000  may include a processor (e.g., a microprocessor or a microcontroller) configured to receive (e.g., through the ADC  1062 ) the estimate of peak current from the peak detection circuit  1070 , receive (e.g., through the ADC  1064 ) the estimate of valley current from the valley detection circuit  1072 , and determine a prediction of a current in a rectifier (e.g., the rectifier  130 ) based on the estimate of peak current and the estimate of valley current. For example, the prediction of the rectified current may be determined based on the estimates of peak current and valley current in a transformer (e.g., the transformer  110 ) using a model converter implemented using a look-up table and/or a mathematical formula. 
     When conductors (e.g., traces or wires) connected to terminals of a transformer (TRF− and TRF+) are close together a coil for sensing current from the transformer may be positioned in the middle, between the conductors of the TRF− and TRF+ terminals. In some implementations, multiple coils connected in series may be used to capture more flux and induce more voltage. Another significant motivation to use multiple coils may be for canceling any stray flux, similar to a differential measurement. For example, one coil may be positioned in the middle of TRF− and TRF+ terminals. For example, three coils may be used, with one positioned between the conductors for the transformer terminals TRF+ and TRF−, and two coils positioned on respective opposite sides of the conductors from the first coil. For example, alternate coils may be wound 180 degrees out of phase. 
       FIG.  11    is a circuit diagram of an example of a system  1100  including a power converter with a coil  1150  for sensing current. The system  1100  includes the transformer  210  and the rectifier  220  of  FIG.  2   , connected by the first trace  240  and the second trace  242  on a layer of a circuit board. The system  1100  includes a coil  1150  including one or more turns of trace on the layer of the circuit board, adjacent to the first trace  240  and adjacent to the second trace  242 . The coil  1150  is connected between terminals of a measurement circuit (e.g., the measurement circuit  160 ) (not shown in  FIG.  11   ). 
     The system  1100  includes a first trace  240  on a layer of a circuit board. The first trace  240  connects the first tap  216  to the rectifier  220 . The system  1100  includes a second trace  242  on the layer of the circuit board. The second trace  242  connects the second tap  218  to the rectifier  220 . The second trace  242  may be connected in series with the first trace  240 . 
     The system  1100  includes a coil  1150  including one or more turns of trace on the layer of the circuit board, adjacent to the first trace  240 . The coil  1150  is adjacent to the second trace  242 . For example, the coil  1150  may be positioned between (e.g., halfway between) the first trace  240  and the second trace  242 . In some implementations, the coil  1150  is positioned to inductively couple to the second trace  242 , and the coil  1150  is positioned to inductively couple to the first trace  240 . 
     In some implementations (not shown in  FIG.  11   ), a coil may be positioned coplanar with a first length of conductor (e.g., a wire or a trace) and a second length of conductor bearing current from the transformer  210  to and from a rectifier. Thus, the coil does not necessarily need to be implemented on a circuit board with traces. Such a system may include a coil including two or more turns of conductor in a spiral arrangement that is coplanar with the first length of conductor, and adjacent to the first length of conductor. The coil may also be coplanar with the second length of conductor, and adjacent to the second length of conductor. The coil may be connected between terminals of a measurement circuit (e.g., the measurement circuit  160 ). 
       FIG.  12    is a circuit diagram of an example of a system  1200  including a power converter with three coils in series for sensing current. The system  1200  includes the transformer  210  and the rectifier  220  of  FIG.  2   , connected by the first trace  240  and the second trace  242  on a layer of a circuit board. The system  1200  includes a first coil  1250  including one or more turns of trace on the layer of the circuit board, adjacent to the first trace  240  and adjacent to the second trace  242 . The system  1200  includes a second coil  1260  including one or more turns of trace on the layer of the circuit board, adjacent to the first trace  240 , on an opposite side of the first trace  240  from the first coil  1250 . The system  1200  includes a third coil  1270  including one or more turns of trace on the layer of the circuit board, adjacent to the second trace  242 , on an opposite side of the second trace  242  from the first coil  1250 . The first coil  1250  is connected in series with the second coil  1260  and the third coil  1270  between terminals of a measurement circuit (e.g., the measurement circuit  160 ) (not shown in  FIG.  12   ). 
     The system  1200  includes a first trace  240  on a layer of a circuit board. The first trace  240  connects the first tap  216  to the rectifier  220 . The system  1200  includes a second trace  242  on the layer of the circuit board. The second trace  242  connects the second tap  218  to the rectifier  220 . The second trace  242  may be connected in series with the first trace  240 . 
     The system  1200  includes a first coil  1250  including one or more turns of trace on the layer of the circuit board, adjacent to the first trace  240 . The first coil  1250  is adjacent to the second trace  242 . For example, the first coil  1250  may be positioned between (e.g., halfway between) the first trace  240  and the second trace  242 . In some implementations, the first coil  1250  is positioned to inductively couple to the second trace  242 , and the first coil  1250  is positioned to inductively couple to the first trace  240 . 
     The system  1200  includes a second coil  1260  including one or more turns of trace on the layer of the circuit board, adjacent to the first trace  240 , on an opposite side of the first trace  240  from the first coil  1250 . In some implementations, the second coil  1260  is positioned to inductively couple to the first trace  240 . For example, the first coil  1250  and the second coil  1260  have opposite winding directions. 
     The system  1200  includes a third coil  1270  including one or more turns of trace on the layer of the circuit board, adjacent to the second trace  242 , on an opposite side of the second trace  242  from the first coil  1250 . In some implementations, the third coil  1270  is positioned to inductively couple to the second trace  242 . For example, the first coil  1250  and the third coil  1270  have opposite winding directions. The third coil  1270  is connected in series with the second coil  1260  and the first coil  1250  between terminals of a measurement circuit (e.g., the measurement circuit  160 ) (not shown in  FIG.  12   ). 
     In some implementations (not shown in  FIG.  12   ), a coil may be positioned coplanar with a first length of conductor (e.g., a wire or a trace) and a second length of conductor bearing current from the transformer  210  to and from a rectifier. Thus, the coil does not necessarily need to be implemented on a circuit board with traces. Such a system may include a transformer including a secondary winding that connects a first tap and a second tap; a first length of conductor that connects the first tap to a rectifier; a first coil including two or more turns of conductor in a spiral arrangement that is coplanar with the first length of conductor, and adjacent to the first length of conductor; a second length of conductor that connects the second tap to the rectifier, wherein the first coil is coplanar with the second length of conductor, and adjacent to the second length of conductor; a second coil including two or more turns of conductor in a spiral arrangement that is coplanar with the first length of conductor, adjacent to the first length of conductor, on an opposite side of the first length of conductor from the first coil; and a third coil including two or more turns of conductor in a spiral arrangement that is coplanar with the second length of conductor, adjacent to the second length of conductor, on an opposite side of the second length of conductor from the first coil. The third coil may be connected in series with the second coil and the first coil between terminals of a measurement circuit (e.g., the measurement circuit  160 ) configured to estimate current flowing in the first length of conductor based on integration over time of voltage across the first coil. 
     When the transformer currents are high, interleaving conductors on alternate layers is one way for transformer connections to minimize losses on a circuit board (e.g., a PCB). For example, conductors connected to TRF+ and TRF− terminals may occur on respective alternate layers (e.g., stacked on top of one another). Hence, flux generated may be alternating on successive layers of the PCB. With this interleaved circuit board layout, a corresponding stack of current sensor coils may have alternate winding directions on each layer to align well with the magnetic field created on alternate PCB layers. 
       FIG.  13    is a circuit diagram of an example of a system  1300  including a power converter with a stack of interleaved conductors on multiple layers of a circuit board and a stack of coils with alternating winding directions for sensing current in the interleaved conductors. The system  1300  includes the transformer  210  and the rectifier  220  of  FIG.  2   , connected by the first trace  1340  and the second trace  1342  on different layers of a circuit board (e.g., stacked vertically). The system  1300  includes an alternating stack of coils  1350 , near the first trace  1340  and the second trace  1342  on their respective layers. The winding directions of the coils in the alternating stack of coils  1350  alternate between layers in correspondence to the polarities of connections of the conductors on those layers (e.g., to the TRF+ and TRF− terminals of the transformer  210 ). The coils of the alternating stack of coils  1350  are connected in series between terminals of a measurement circuit (e.g., the measurement circuit  160 ) (not shown in  FIG.  13   ). 
     The system  1300  includes a first trace  1340  on a layer of a circuit board. The first trace  1340  connects the first tap  216  to the rectifier  220 . The system  1300  includes a second trace  1342  on an additional layer of the circuit board, stacked vertically with the first trace  1340 . The second trace  1342  connects the second tap  218  to the rectifier  220 . The second trace  1342  may be connected in series with the first trace  1340 . 
     The system  1300  includes an alternating stack of coils  1350 . For example, the alternating stack of coils  1350  may include a first coil including one or more turns of trace on the layer of the circuit board, adjacent to the first trace  1340 . In some implementations, the first coil is positioned to inductively couple to the first trace  1340 . For example, the alternating stack of coils  1350  may include a second coil including one or more turns of trace on the additional layer of the circuit board, stacked vertically with the first coil. The first coil and the second coil may have opposite winding directions. The second coil may be connected in series with the first coil between terminals of a measurement circuit (e.g., the measurement circuit  160 ) (not shown in  FIG.  13   ). For example, the alternating stack of coils  1350  may include the alternating stack of coils  1420  of  FIG.  14   . 
     In some implementations (not shown in  FIG.  13   ), a second alternating stack of coils may be positioned on an opposite side of the first trace  1340  and the second trace  1342  from the alternating stack of coils  1350 . This second alternating stack of coils may have opposite winding directions with respect to the alternating stack of coils  1350  on each layer. The second alternating stack of coils may be connected in series with the alternating stack of coils  1350  between terminals of a measurement circuit (e.g., the measurement circuit  160 ) to capture more flux caused by current flowing in the first trace  1340  and the second trace  1342 . 
     In some implementations (not shown in  FIG.  13   ), conductors connected to the terminals of the transformer  210  may be interleaved on more layers (e.g., on 4 layers or 8 layers of a circuit board), so that current flows in each direction on multiple layers in parallel to reduce the current on individual layers. A larger stack of coils with winding directions alternating in correspondence to the interleaved stack of conductors may be used. For example, the alternating stack of coils may include the alternating stack of coils  1520  of  FIG.  15   . 
       FIG.  14    is an illustration of an example of a system  1400  including a two-layer circuit board with a stack of coils in series with alternating winding directions for sensing current. The system  1400  includes a two-layer circuit board (e.g., a PCB) that includes a first layer  1410  (e.g., a top layer) and a second layer  1412  (e.g., a hidden layer or a bottom layer). The system  1400  includes an alternating stack of coils  1420  that each include one or more turns of trace (e.g., copper trace) on a respective layer of the circuit board. The alternating stack of coils  1420  is connected in series by a via  1460 . The alternating stack of coils  1420  is connected to a first terminal  1440  on the first layer  1410 . The alternating stack of coils  1420  is connected to a second terminal  1442  on the second layer  1412 . For example, the coils ( 1430  and  1432 ) of the alternating stack of coils  1420  may have the alternating winding directions, with coils on adjacent layers having opposite winding directions. For example, the alternating stack of coils  1420  may be used to implement a current sensor of the system  100  of  FIG.  1    or of the system  1300  of  FIG.  13   . 
     The system  1400  includes a first coil  1430  on the first layer  1410 . Although not shown in  FIG.  14   , the first layer  1410  may also include a first trace (e.g., connected to a TRF+ terminal of a transformer) that is adjacent to and/or inductively coupled to the first coil  1430 . This first trace may bear a time varying current that is measured using a current sensor that includes the alternating stack of coils  1420  (e.g., as described in relation to  FIG.  1   ). The system includes a second coil  1432  including one or more turns of trace on an additional layer (i.e., the second layer  1412 ) of the circuit board, stacked vertically with the first coil  1430 . Although not shown in  FIG.  14   , the second layer  1412  may also include a second trace (e.g., connected to a TRF− terminal of a transformer) that is adjacent to and/or inductively coupled to the second coil  1432 . The second coil  1432  is connected in series with the first coil  1430  between terminals (e.g., the first terminal  1440  and the second terminal  1442 ) of a measurement circuit (e.g., the measurement circuit  160 ) (not shown in  FIG.  14   ). The second coil  1432  is connected to the first coil  1430  by the via  1460 . 
     Although not shown in  FIG.  14   , the coils ( 1430  and  1432 ) of the alternating stack of coils  1420  may include additional turns of trace (e.g., in a spiral arrangement) to capture more flux. 
       FIG.  15    is an illustration of an example of a system  1500  including a four-layer circuit board with a stack of coils in series with alternating winding directions for sensing current. The system  1500  includes a four-layer circuit board (e.g., a PCB) that includes a first layer  1510  (e.g., a top layer), a second layer  1512  (e.g., a hidden layer), a third layer  1514  (e.g., a hidden layer), and a fourth layer  1516  (e.g., a bottom layer). The system  1500  includes an alternating stack of coils  1520  that each include one or more turns of trace (e.g., copper trace) on a respective layer of the circuit board. The alternating stack of coils  1520  is connected in series by vias ( 1560 ,  1562 , and  1564 ). The alternating stack of coils  1520  is connected to a first terminal  1540  on the first layer  1510 . The alternating stack of coils  1520  is connected to a second terminal  1542  on the fourth layer  1516 . For example, the coils ( 1530 ,  1532 ,  1534 , and  1536 ) of the alternating stack of coils  1520  may have the alternating winding directions, with coils on adjacent layers having opposite winding directions. For example, the alternating stack of coils  1520  may be used to implement a current sensor of the system  100  of  FIG.  1    or of the system  1300  of  FIG.  13   . 
     The system  1500  includes a first coil  1530  on the first layer  1510 . Although not shown in  FIG.  15   , the first layer  1510  may also include a first trace (e.g., connected to a TRF+ terminal of a transformer) that is adjacent to and/or inductively coupled to the first coil  1530 . This first trace may bear a time varying current that is measured using a current sensor that includes the alternating stack of coils  1520  (e.g., as described in relation to  FIG.  1   ). The system includes a second coil  1532  including one or more turns of trace on an additional layer (i.e., the second layer  1512 ) of the circuit board, stacked vertically with the first coil  1530 . Although not shown in  FIG.  15   , the second layer  1512  may also include a second trace (e.g., connected to a TRF− terminal of a transformer) that is adjacent to and/or inductively coupled to the second coil  1532 . The second coil  1532  is connected in series with the first coil  1530  between terminals (e.g., the first terminal  1540  and the second terminal  1542 ) of a measurement circuit (e.g., the measurement circuit  160 ) (not shown in  FIG.  15   ). The second coil  1532  is connected to the first coil  1530  by the via  1560 . The system includes a third coil  1534  including one or more turns of trace on an additional layer (i.e., the third layer  1514 ) of the circuit board, stacked vertically with the first coil  1530 . Although not shown in  FIG.  15   , the third layer  1514  may also include a third trace (e.g., connected to a TRF+ terminal of a transformer) that is adjacent to and/or inductively coupled to the third coil  1534 . The third coil  1534  is connected in series with the first coil  1530  between terminals (e.g., the first terminal  1540  and the second terminal  1542 ) of a measurement circuit. The third coil  1534  is connected to the second coil  1532  by the via  1562 . The system includes a fourth coil  1536  including one or more turns of trace on an additional layer (i.e., the fourth layer  1516 ) of the circuit board, stacked vertically with the first coil  1530 . Although not shown in  FIG.  15   , the fourth layer  1516  may also include a fourth trace (e.g., connected to a TRF− terminal of a transformer) that is adjacent to and/or inductively coupled to the fourth coil  1536 . The fourth coil  1536  is connected in series with the first coil  1530  between terminals (e.g., the first terminal  1540  and the second terminal  1542 ) of a measurement circuit. The fourth coil  1536  is connected to the third coil  1534  by the via  1564 . 
     Although not shown in  FIG.  15   , the coils ( 1530 ,  1532 ,  1534 , and  1536 ) of the alternating stack of coils  1520  may include additional turns of trace (e.g., in a spiral arrangement) to capture more flux. 
       FIG.  16    is a circuit diagram of an example of a system  1600  including a power converter with a stack of interleaved conductors on multiple layers of a circuit board and one or more coils with interlayer turns for sensing current in the interleaved conductors. The system  1600  includes the transformer  210  and the rectifier  220  of  FIG.  2   , connected by the first trace  1340  and the second trace  1342  on different layers of a circuit board (e.g., stacked vertically). The system  1300  includes one or more coils  1650  with interlayer turns, near the first trace  1340  and the second trace  1342  on their respective layers. The one or more coils  1650  are connected in series between terminals of a measurement circuit (e.g., the measurement circuit  160 ) (not shown in  FIG.  16   ). 
     The system  1600  includes a first trace  1340  on a layer of a circuit board. The first trace  1340  connects the first tap  216  to the rectifier  220 . The system  1600  includes a second trace  1342  on an additional layer of the circuit board, stacked vertically with the first trace  1340 . The second trace  1342  connects the second tap  218  to the rectifier  220 . The second trace  1342  may be connected in series with the first trace  1340 . 
     The system  1600  includes one or more coils  1650  with interlayer turns, which may be stacked horizontally. An interlayer turn includes traces on multiple layers of a circuit board and conductors (e.g., vias or through-holes) connecting the layers. For example, a turn of coil may span two adjacent layers, being oriented approximately orthogonally to the plane of the circuit board, with the center of the turn being positioned between the two adjacent layers. In some implementations, interlayer turns of coil may be stacked horizontally within the circuit, from closer to farther from a pair if interleaved conductors, such as the first trace  1340  and the second trace  1342 . The one or more coils  1650  with interlayer turns may be connected in series between terminals of a measurement circuit (e.g., the measurement circuit  160 ) (not shown in  FIG.  16   ). 
     In some implementations (not shown in  FIG.  16   ), conductors connected to the terminals of the transformer  210  may be interleaved on more layers (e.g., on 4 layers or 8 layers of a circuit board), so that current flows in each direction on multiple layers in parallel to reduce the current on individual layers. A larger vertical stack of coils with one or more coils with interlayer turns corresponding to respective pairs of conductors in the interleaved stack of conductors may be used. For example, the one or more coils  1650  with interlayer turns may include the coils  1720  with interlayer turns of  FIG.  17   . For example, the one or more coils  1650  with interlayer turns may include the coils  1820  with interlayer turns of  FIG.  18    that include pairs of horizontally stacked coils. 
       FIG.  17    is an illustration of an example of a system  1700  including a four-layer circuit board with two coils with interlayer turns for sensing current. The system  1700  includes a four-layer circuit board (e.g., a PCB) that includes a first layer  1710  (e.g., a top layer), a second layer  1712  (e.g., a hidden layer), a third layer  1714  (e.g., a hidden layer), and a fourth layer  1716  (e.g., a bottom layer). The system  1700  includes a vertical stack of coils  1720  with interlayer turns. For example, a first interlayer turn spans the first layer  1710  and the second layer  1712 . The first interlayer turn includes a trace  1730  (e.g., a copper trace), a via  1740 , a trace  1732 , and the via  1746 . For example, the first interlayer turn may be positioned adjacent to a pair of interleaved conductors (e.g., the first trace  1340  and the second trace  1342  of  FIG.  16   ) (not shown in  FIG.  17   ) on the first layer  1710  and the second layer  1712 . For example, the first interlayer turn may be positioned to inductively couple to a pair of interleaved conductors. For example, a second interlayer turn spans the third layer  1714  and the fourth layer  1716 . The second interlayer turn includes a trace  1734  (e.g., a copper trace), a via  1744 , a trace  1736 , and the via  1746 . For example, the second interlayer turn may be positioned adjacent to a second pair of interleaved conductors (e.g., respectively connected to TRF+ terminal and a TRF− terminal of a transformer) (not shown in  FIG.  17   ) on the third layer  1714  and the fourth layer  1716 . For example, the second interlayer turn may be positioned to inductively couple to the second pair of interleaved conductors. The vertical stack of coils  1720  is connected by a via  1742  and the via  1746 . The vertical stack of coils  1720  is connected to a first terminal  1750  and a second terminal  1752  on the first layer  1710 . For example, the vertical stack of coils  1720  may be used to implement a current sensor of the system  100  of  FIG.  1    or of the system  1600  of  FIG.  16   . The vertical stack of coils  1720  is connected between terminals (e.g., the first terminal  1750  and the second terminal  1752 ) of a measurement circuit (e.g., the measurement circuit  160 ) (not shown in  FIG.  17   ). 
       FIG.  18    is an illustration of an example of a system  1800  including a four-layer circuit board with two horizontal stacks of coils with interlayer turns for sensing current. The system  1800  includes a four-layer circuit board (e.g., a PCB) that includes a first layer  1810  (e.g., a top layer), a second layer  1812  (e.g., a hidden layer), a third layer  1814  (e.g., a hidden layer), and a fourth layer  1816  (e.g., a bottom layer). The system  1800  includes a vertical stack of coils  1820  with interlayer turns, including pairs of horizontally stacked interlayer turns. For example, a first interlayer turn spans the first layer  1810  and the second layer  1812 . The first interlayer turn includes a trace  1830  (e.g., a copper trace), a via  1840 , a trace  1831 , and a via  1841 . For example, the first interlayer turn may be positioned adjacent to a pair of interleaved conductors (e.g., the first trace  1340  and the second trace  1342  of  FIG.  16   ) (not shown in  FIG.  18   ) on the first layer  1810  and the second layer  1812 . For example, the first interlayer turn may be positioned to inductively couple to a pair of interleaved conductors. For example, a second interlayer turn spans the first layer  1810  and the second layer  1812 . The second interlayer turn includes a trace  1832  (e.g., a copper trace), a via  1842 , a trace  1832 , and a via  1847 . For example, the second interlayer turn may be positioned to inductively couple to a pair of interleaved conductors (e.g., the first trace  1340  and the second trace  1342  of  FIG.  16   ) (not shown in  FIG.  18   ) on the first layer  1810  and the second layer  1812 . The second interlayer turn is horizontally stacked with the first interlayer turn, positioned slightly farther from the pair of interleaved conductors. For example, a third interlayer turn spans the third layer  1814  and the fourth layer  1816 . The third interlayer turn includes a trace  1834  (e.g., a copper trace), a via  1844 , a trace  1835 , and a via  1845 . For example, the third interlayer turn may be positioned adjacent to a pair of interleaved conductors (not shown in  FIG.  18   ) on the third layer  1814  and the fourth layer  1816 . For example, the third interlayer turn may be positioned to inductively couple to a pair of interleaved conductors. For example, a fourth interlayer turn spans the third layer  1814  and the fourth layer  1816 . The fourth interlayer turn includes a trace  1836  (e.g., a copper trace), a via  1846 , a trace  1837 , and the via  1847 . For example, the fourth interlayer turn may be positioned to inductively couple to a pair of interleaved conductors (not shown in  FIG.  18   ) on the third layer  1814  and the fourth layer  1816 . The fourth interlayer turn is horizontally stacked with the third interlayer turn, positioned slightly farther from the pair of interleaved conductors. The vertical stack of coils  1820  is connected by via  1843  and the via  1847 . The vertical stack of coils  1820  is connected to a first terminal  1850  and a second terminal  1852  on the first layer  1810 . For example, the vertical stack of coils  1820  may be used to implement a current sensor of the system  100  of  FIG.  1    or of the system  1600  of  FIG.  16   . The vertical stack of coils  1820  is connected between terminals (e.g., the first terminal  1850  and the second terminal  1852 ) of a measurement circuit (e.g., the measurement circuit  160 ) (not shown in  FIG.  18   ). 
     As described above, one aspect of the present technology is the gathering and use of data available from various sources. The present disclosure contemplates that in some instances, this gathered data may include personal information data that uniquely identifies or can be used to contact or locate a specific person. Such personal information data can include demographic data, location-based data, telephone numbers, email addresses, twitter ID&#39;s, home addresses, data or records relating to a user&#39;s health or level of fitness (e.g., vital signs measurements, medication information, exercise information), date of birth, or any other identifying or personal information. 
     The present disclosure recognizes that the use of such personal information data, in the present technology, can be used to the benefit of users. For example, the personal information data can be used to adjust power consumption profiles for an associated device. Further, other uses for personal information data that benefit the user are also contemplated by the present disclosure. For instance, health and fitness data may be used to provide insights into a user&#39;s general wellness, or may be used as positive feedback to individuals using technology to pursue wellness goals. 
     The present disclosure contemplates that the entities responsible for the collection, analysis, disclosure, transfer, storage, or other use of such personal information data will comply with well-established privacy policies and/or privacy practices. In particular, such entities should implement and consistently use privacy policies and practices that are generally recognized as meeting or exceeding industry or governmental requirements for maintaining personal information data private and secure. Such policies should be easily accessible by users, and should be updated as the collection and/or use of data changes. Personal information from users should be collected for legitimate and reasonable uses of the entity and not shared or sold outside of those legitimate uses. Further, such collection/sharing should occur after receiving the informed consent of the users. Additionally, such entities should consider taking any needed steps for safeguarding and securing access to such personal information data and ensuring that others with access to the personal information data adhere to their privacy policies and procedures. Further, such entities can subject themselves to evaluation by third parties to certify their adherence to widely accepted privacy policies and practices. In addition, policies and practices should be adapted for the particular types of personal information data being collected and/or accessed and adapted to applicable laws and standards, including jurisdiction-specific considerations. For instance, in the US, collection of or access to certain health data may be governed by federal and/or state laws, such as the Health Insurance Portability and Accountability Act (HIPAA); whereas health data in other countries may be subject to other regulations and policies and should be handled accordingly. Hence different privacy practices should be maintained for different personal data types in each country. 
     Despite the foregoing, the present disclosure also contemplates embodiments in which users selectively block the use of, or access to, personal information data. That is, the present disclosure contemplates that hardware and/or software elements can be provided to prevent or block access to such personal information data. For example, in the case of location aware services, the present technology can be configured to allow users to select to “opt in” or “opt out” of participation in the collection of personal information data during registration for services or anytime thereafter. In addition to providing “opt in” and “opt out” options, the present disclosure contemplates providing notifications relating to the access or use of personal information. For instance, a user may be notified upon downloading an app that their personal information data will be accessed and then reminded again just before personal information data is accessed by the app. 
     Moreover, it is the intent of the present disclosure that personal information data should be managed and handled in a way to minimize risks of unintentional or unauthorized access or use. Risk can be minimized by limiting the collection of data and deleting data once it is no longer needed. In addition, and when applicable, including in certain health related applications, data de-identification can be used to protect a user&#39;s privacy. De-identification may be facilitated, when appropriate, by removing specific identifiers (e.g., date of birth, etc.), controlling the amount or specificity of data stored (e.g., collecting location data a city level rather than at an address level), controlling how data is stored (e.g., aggregating data across users), and/or other methods. 
     Therefore, although the present disclosure broadly covers use of personal information data to implement one or more various disclosed embodiments, the present disclosure also contemplates that the various embodiments can also be implemented without the need for accessing such personal information data. That is, the various embodiments of the present technology are not rendered inoperable due to the lack of all or a portion of such personal information data. For example, power consumption can be adjusted based on non-personal information data or a bare minimum amount of personal information, such as the content being requested by the device associated with a user, other non-personal information available to the vehicle or associated computing device, or publicly available information.

Metadata:
Filing Date: 20191219
Publication Date: 20241022
Grant Date: 20241022
Priority Date: 20181228
Inventors: PIERQUET, BRANDON
Sahoo, Ashish K.
GAMACHE, GARET E.
LU, JIE
Assignee: APPLE INC
CPC Classifications: [{"code": "H02M3/28", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02M1/0009", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01F2027/2809", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01F27/2804", "inventive": true, "first": false, "tree": "[]"}, {"code": "G01R15/181", "inventive": true, "first": false, "tree": "[]"}, {"code": "H05K1/0298", "inventive": true, "first": false, "tree": "[]"}, {"code": "H05K2201/09227", "inventive": false, "first": false, "tree": "[]"}, {"code": "H03K5/24", "inventive": true, "first": true, "tree": "[]"}, {"code": "H02M1/0009", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K1/0298", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01F2027/2809", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K2201/09227", "inventive": false, "first": false, "tree": "[]"}, {"code": "H03K5/24", "inventive": true, "first": false, "tree": "[]"}, {"code": "G01R15/181", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01F27/2804", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02M3/24", "inventive": true, "first": true, "tree": "[]"}, {"code": "H05K2201/09227", "inventive": false, "first": false, "tree": "[]"}, {"code": "H02M1/0009", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01F2027/2809", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K1/0298", "inventive": true, "first": false, "tree": "[]"}, {"code": "H03K5/24", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01F27/2804", "inventive": true, "first": false, "tree": "[]"}, {"code": "G01R15/181", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02M3/24", "inventive": true, "first": true, "tree": "[]"}]
Family ID: 93123403