PATENT DOCUMENT

Publication Number: US-9048743-B2
Application Number: US-201213570031-A
Country: US
Kind Code: B2

Title: Controlling an adapter transformer voltage

Abstract:
An adapter for electrical power that includes a rectifier coupled to a transformer with a primary coil and a secondary coil. The secondary coil includes a first end tap, a second end tap, and a center tap. A first switch is coupled between the first end tap and a primary side ground. A second switch is coupled between the second end tap and the primary side ground. A controller is coupled to the first switch and to the second switch so that during one or more intervals, the first switch and the second switch are alternately open and closed a predetermined number of times, wherein the initial switch closed each interval alternates between the first switch and the second switch, and after the predetermined number of times, both the first switch and the second switch are opened for a predetermined time period.

Claims:
What is claimed is: 
     
       1. An adapter for electrical power, comprising:
 a rectifier with an input and an output; 
 a transformer with a primary coil and a secondary coil, wherein the primary coil includes a center tap coupled to the output of the rectifier, and a first end tap and a second end tap; 
 a first switch coupled between the first end tap and a primary side ground; 
 a second switch coupled between the second end tap and the primary side ground; and 
 a controller coupled to the first switch and to the second switch and configured to control the first switch and the second switch so that during each of one or more intervals,
 the first switch and the second switch are alternately open and closed a predetermined number of times, wherein at each interval an initial switch that is closed at the beginning of the interval alternates between the first switch and the second switch, and wherein after the predetermined number of times, both the first switch and the second switch are opened for a predetermined time period, wherein the controller is further configured so that a duration that the initial switch is closed during a first of the predetermined number of times is equal to a duration that a switch is closed during a last of the predetermined number of times, and the duration that the initial switch is closed during the first of the predetermined number of times is equal to one half of a duration that a switch is closed during a second of the predetermined number of times. 
 
 
     
     
       2. The adapter of  claim 1 , further comprising:
 an inductor coupled between the output of the rectifier and the center tap of the primary coil. 
 
     
     
       3. The adapter of  claim 1 , further comprising:
 a first diode with an anode and a cathode; and 
 a second diode with an anode and a cathode, wherein the secondary coil further comprises a center tap coupled to a secondary side ground, a first end tap coupled to the anode of the first diode and a second end tap coupled to the anode of the second diode, wherein the cathode of the first diode is coupled to the cathode of the second diode. 
 
     
     
       4. The adapter of  claim 3 , further comprising:
 a second inductor coupled between the center tap of the secondary coil and the secondary side ground. 
 
     
     
       5. The adapter of  claim 1 , wherein the controller is further configured so that a total duration that the first switch is closed during each interval is equal to a total duration that the second switch is closed during each interval. 
     
     
       6. The adapter of  claim 1 , wherein the controller is further configured so that at least one of a frequency at which the first switch and the second switch are alternately open and closed, the predetermined number of times the first switch and the second switch are alternately open and closed, and the predetermined time period is changed based on a power demand from the adapter. 
     
     
       7. An adapter for electrical power, comprising:
 a first rectifier with an input and an output; 
 an H-bridge with an input and an output, wherein the output of the first rectifier is coupled to the input of the H-bridge; 
 a transformer with a primary coil and a secondary coil, wherein the primary coil is coupled to the output of the H-bridge; 
 a second rectifier with an input and an output, wherein the secondary coil is coupled to the input of the second rectifier; and 
 a controller coupled to the H-bridge and configured to control the H-bridge to alternate a polarity of a voltage across the primary coil between a first polarity and a second polarity a predetermined number of times, wherein a start polarity of the voltage across the primary coil during each interval alternates between the first polarity and the second polarity, and wherein after the predetermined number of times, the controller is configured to create an open circuit between the first rectifier and the primary coil for a predetermined time period, wherein the controller is further configured so that a duration of the start polarity during a first of the predetermined number of times is equal to a duration of an end polarity of the voltage across the primary coil during a last of the predetermined number of times, and a duration of each alternation of the polarity of the voltage across the primary coil after the first of the predetermined number of times and before the last of the predetermined number of times is twice the duration of the start polarity during the first of the predetermined number of times. 
 
     
     
       8. The adapter of  claim 7 , wherein the controller is further configured so that a total duration of the first polarity during the predetermined number of times is equal to a total duration of the second polarity during the predetermined number of times. 
     
     
       9. The adapter of  claim 7 , further comprising:
 an inductor coupled between the output of the H-bridge and the primary coil. 
 
     
     
       10. The adapter of  claim 7 , wherein the controller is further configured so that at least one of a frequency at which the polarity of the voltage across the primary coil is alternated, the predetermined number of times the polarity of the voltage pulse across the primary coil is alternated, and the predetermined time period is changed based on a power demand from the adapter. 
     
     
       11. An adapter for electrical power, comprising:
 a rectifier with an input and an output; 
 a half H-bridge with an input and an output, wherein the output of the rectifier is coupled to the input of the half H-bridge; 
 a transformer with a primary coil and a secondary coil, wherein the primary coil has a first end tap and a second end tap and the first end tap is coupled to the output of the half H-bridge, and wherein the secondary coil has a center tap coupled to a secondary side ground, and a third end tap and a fourth end tap; 
 a capacitor coupled between the second end tap of the primary coil and a primary side ground; 
 a first diode with an anode and a cathode; 
 a second diode with an anode and a cathode, wherein the third end tap of the secondary coil is coupled to the anode of the first diode and the fourth end tap of the secondary coil is coupled to the anode of the second diode, wherein the cathode of the first diode is coupled to the cathode of the second diode; and 
 a controller coupled to the half H-bridge and configured to control the half H-bridge to alternate a polarity of a voltage across the primary coil between a first polarity and a second polarity a predetermined number of times, wherein a start polarity of the voltage across the primary coil during each interval alternates between the first polarity and the second polarity, and wherein after the predetermined number of times, the controller is configured to create an open circuit between the first rectifier and the primary coil for a predetermined time period, wherein the controller is further configured so that a duration of the start polarity during a first of the predetermined number of times is equal to a duration of an end polarity of the voltage across the primary coil during a last of the predetermined number of times, and a duration of each alternation of the polarity of the voltage across the primary coil after the first of the predetermined number of times and before the last of the predetermined number of times is twice the duration of the start polarity during the first of the predetermined number of times. 
 
     
     
       12. The adapter of  claim 11 , wherein the controller is further configured so that a total duration of the first polarity during the predetermined number of times is equal to a total duration of the second polarity during the predetermined number of times. 
     
     
       13. The adapter of  claim 11 , further comprising:
 an inductor coupled between the output of the half H-bridge and the first end tap of the primary coil. 
 
     
     
       14. The adapter of  claim 11 , further comprising:
 a second inductor coupled between the center tap and the secondary side ground. 
 
     
     
       15. The adapter of  claim 11 , wherein the controller is further configured so that at least one of a frequency at which the polarity of the voltage across the primary coil is alternated, the predetermined number of times the polarity of the voltage pulse across the primary coil is alternated, and the predetermined time period is changed based on a power demand from the adapter.

Description:
BACKGROUND 
     1. Field 
     The present embodiments relate to power adapters. More specifically, the present embodiments relate to controlling a power adapter transformer voltage. 
     2. Related Art 
     Power adapters that are designed to supply power to electronic devices such as laptop computers often include a power factor correction (PFC) circuit. Typically, the PFC circuit steps-up the input voltage to a higher voltage, and in order to safely handle this voltage, the PFC circuit must include one or more high-voltage components. These components are often physically large and may take up a sizable portion of the adapter volume, which may interfere with other design considerations for the adapter. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG. 1  shows a power adapter including an H-bridge and a transformer with a center-tapped secondary coil in accordance with an embodiment. 
         FIG. 2A  depicts an exemplary graph of a control signal controlling two switches in an H-bridge coupled to the primary coil of a transformer in accordance with an embodiment. 
         FIG. 2B  depicts an exemplary graph of a control signal controlling two other switches in an H-bridge coupled to the primary coil of a transformer in accordance with an embodiment. 
         FIG. 2C  depicts an exemplary graph of the voltage across the primary coil of an adapter transformer in accordance with an embodiment. 
         FIG. 2D  depicts an exemplary graph of the flux in the transformer due to the voltage across the coil depicted in  FIG. 2C  in accordance with an embodiment. 
         FIG. 3A  depicts an exemplary graph of the variation of control parameters for a controller controlling the voltage across the primary coil of an adapter transformer vs. output power of the adapter in accordance with an embodiment. 
         FIG. 3B  depicts an exemplary graph of cycle frequency of the voltage across the primary coil of an adapter transformer vs. output power of the adapter in accordance with an embodiment. 
         FIG. 4A  depicts an exemplary graph of an alternate control signal controlling two switches in an H-bridge coupled to the primary coil of a transformer in accordance with an embodiment. 
         FIG. 4B  depicts an exemplary graph of an alternate control signal controlling two other switches in an H-bridge coupled to the primary coil of a transformer in accordance with an embodiment. 
         FIG. 4C  depicts an exemplary graph of the voltage across the primary coil of an adapter transformer due to the alternate control signal in accordance with an embodiment. 
         FIG. 4D  depicts an exemplary graph of the flux in the transformer due to the voltage across the coil depicted in  FIG. 4C  in accordance with an embodiment. 
         FIG. 5  shows an adapter similar to the embodiment of  FIG. 1  that includes two additional inductors in accordance with an embodiment. 
         FIG. 6  shows an adapter including a half H-bridge and a center-tapped secondary coil in accordance with an embodiment. 
         FIG. 7  shows an adapter similar to the embodiment of  FIG. 6  that includes two additional inductors in accordance with an embodiment. 
         FIG. 8  shows another adapter including an H-bridge in accordance with an embodiment. 
         FIG. 9  shows another adapter including a center tapped primary coil in accordance with an embodiment. 
         FIG. 10  shows an adapter similar to the embodiment of  FIG. 9  that includes an additional inductor in accordance with an embodiment. 
         FIG. 11  shows another adapter including a center tapped primary coil and a center tapped secondary coil in accordance with an embodiment. 
         FIG. 12  shows an adapter similar to the embodiment of  FIG. 11  that includes two additional inductors in accordance with an embodiment. 
         FIG. 13  shows an adapter similar to the one depicted in  FIG. 1  that includes an inductor between the center tap of the secondary coil and ground, and a switch coupled between one end tap of the secondary coil and ground and another switch coupled between the other end tap of the secondary coil and ground in accordance with an embodiment. 
         FIG. 14A  depicts an exemplary graph of the voltage across the primary coil of an adapter transformer in accordance with an embodiment. 
         FIG. 14B  depicts an exemplary graph of a control signal controlling switch  1304  in accordance with an embodiment. 
         FIG. 14C  depicts an exemplary graph of a control signal controlling switch  1308  in accordance with an embodiment. 
     
    
    
     In the figures, like reference numerals refer to the same figure elements. 
     DETAILED DESCRIPTION 
     The following description is presented to enable any person skilled in the art to make and use the embodiments, and is provided in the context of a particular application and its requirements. Various modifications to the disclosed embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be applied to other embodiments and applications without departing from the spirit and scope of the present disclosure. Thus, the present invention is not limited to the embodiments shown, but is to be accorded the widest scope consistent with the principles and features disclosed herein. 
     The methods and processes described herein can be included in hardware modules or apparatus. These modules or apparatus may include, but are not limited to, an application-specific integrated circuit (ASIC) chip, a field-programmable gate array (FPGA), a dedicated or shared processor that executes a particular software module or a piece of code at a particular time, and/or other programmable-logic devices now known or later developed. When the hardware modules or apparatus are activated, they perform the methods and processes included within them. 
       FIG. 1  shows an adapter in accordance with an embodiment. Alternating current (AC) voltage  102  is coupled to rectifier  104  across capacitor  106  and into H-bridge  108 . Transformer  110  includes primary coil  112  and center tapped secondary coil  114 . Primary coil  112  is coupled to the output of H-bridge  108 , and secondary coil  114  is coupled through diode  116  and diode  118  across capacitor  120  to output  122 . Controller  124  is coupled to and controls switches S 1  through S 4  in H-bridge  108 . 
     AC voltage  102  is any device that outputs an AC voltage and may include but is not limited to a wall plug that can be plugged into an AC voltage outlet. For example, AC voltage  102  may be a standard wall plug that is plugged into an electrical outlet, and may be in any standard available in any country including but not limited to 80 volts to 240 volts AC electricity at from 50 Hz to 60 Hz. In some embodiments, AC voltage  102  also includes a line filter that filters the voltage from AC voltage  102 . 
     Rectifier  104  is a voltage rectifier that converts the positive and negative voltage output from AC voltage  102  into voltage that is positive only. Rectifier  104  may include but is not limited to a full-bridge rectifier, or any other rectifier that outputs only a positive going voltage from an input that is positive and negative, and it may be implemented in any technology. Capacitor  106  may be any suitable capacitor selected based on factors including but not limited to voltage, capacity and leakage requirements, and may be implemented in any technology. 
     H-bridge  108  is any H-bridge that includes four individual switches S 1  to S 4 , each of which is controlled by controller  124 . H-bridge  108  uses switches S 1  to S 4  to control the voltage across primary coil  112  in transformer  110 . For example, when switches S 1  and S 4  are closed and switches S 2  and S 3  are open, the voltage from the top to the bottom of primary coil  112  is positive; when switches S 1  and S 4  are open and switches S 2  and S 3  are closed, the voltage from the top to the bottom of primary coil  112  is negative; and when all switches S 1  to S 4  are open, there is no voltage across primary coil  112 . Note that switches S 1  to S 4  can each be any type of switch implemented in any technology that can switch in response to a control signal. For example, switches S 1  to S 4  may include but are not limited to relays, or transistors such as FETs, including MOSFET transistors, and may be implemented using any combination of discrete and integrated components, and analog and/or digital technology. 
     Transformer  110  can be any transformer with a primary coil and a center tapped secondary coil implemented in any technology. The winding ratio of primary coil  112  to secondary coil  114  can be set to any value based on the input voltage and the desired output voltage. Transformer  110  may be a step-down transformer with a turns ratio between primary coil  112  and secondary coil  114  that may be set to any value based on AC voltage  102  and the desired voltage at output  120 . For example, in some embodiments, for an expected input voltage of 90 to 120 volts from AC voltage  102  and a desired output voltage in the range of 20 to 30 volts, a turns ratio between primary coil  112  and each arm of secondary coil  114  may be chosen to be about 4:1, while for an expected input voltage of 220 to 240 volts from AC voltage  102  for the same desired output voltage range, the turns ratio may be chosen to be about 8:1. In other embodiments, a turns ratio in the range of 4:1 up to 8:1 may be used. Additionally, in some embodiments, a step-up converter is placed after capacitor  120  to step-up the voltage from secondary coil  114  based on a desired power factor of the adapter. In some embodiments, the step-up converter steps-up the voltage to between 40 volts and 50 volts, while in other embodiments, the voltage is stepped-up to a value less than 50 volts. 
     Diode  116  and diode  118  can be any suitable diodes implemented in any technology and may be implemented using any combination of discrete or integrated technology. Capacitor  120  is any suitable capacitor implemented in any technology. 
     Controller  124  is a controller implemented in any combination of hardware and/or software and in any technology, and may include any combination of integrated and discrete components and may be implemented in any hardware module or apparatus. For example, in some embodiments, one or more separate integrated circuit chips perform the indicated operations. In these embodiments, the integrated circuit chips can include specialized circuits that implement some or all of the above-described operations, and/or can include general-purpose circuits that execute program code (e.g., firmware, etc.) that causes the circuits to perform the operations. 
     Controller  124  controls each switch S 1  to S 4  in H-bridge  108  and may be coupled to (not shown) and use input received from rectifier  104  and output  122  to control switches S 1  to S 4 . Note that the input to controller  124  from output  122  may include an isolation device or circuit (not shown) to electrically isolate the secondary side of transformer  110  from the primary side, and may also include a voltage divider (not shown) to reduce the feedback voltage from output  122  to controller  124 . For example, a resistive voltage divider and an opto-isolator may be inserted in a feedback path from output  122  to controller  124 . 
     Output  122  may be coupled to or configured to be coupled to any electronic device that uses direct current (DC) voltage to operate, including but not limited to a laptop computer, a tablet computer, a smartphone, and/or a battery charger. 
     The adapter in  FIG. 1  operates as follows. AC voltage is output from AC voltage  102  and into rectifier  104 . Rectifier  104  rectifies the AC voltage so that it contains only positive going voltage. This voltage is then input into H-bridge  108  and controller  124  controls switches S 1  to S 4  to control the voltage across primary coil  112 . 
       FIGS. 2A and 2B  depict exemplary graphs of control signals from controller  124  controlling, respectively, switches S 1  and S 4 , and switches S 2  and S 3  in H-bridge  108  in accordance with an embodiment.  FIG. 2C  depicts an exemplary graph of the voltage across primary coil  112  as a result of the switching signals depicted in  FIGS. 2A and 2B .  FIG. 2D  depicts an exemplary graph of the flux in transformer  110  due to the voltage across the coil depicted in  FIG. 2C  in accordance with an embodiment. 
     Note that for exemplary purposes only two intervals are depicted in each graph, first interval  202  and second interval  204 . Embodiments may include more or fewer intervals. First interval  202  includes time periods T 1  through T 8  and second interval  204  includes time periods T 9  through T 16 . 
     In time period T 1 , switches S 1  and S 4  are closed while switches S 2  and S 3  are open so that the voltage across primary coil  112  is positive as shown in  FIG. 2C . During time period T 1 , the flux in transformer  110  builds up from zero to its maximum (Φ). Then, in time period T 2 , controller  124  controls switches S 1  and S 4  to open and switches S 2  and S 3  to close so that the voltage across primary coil  112  is negative. During time period T 2 , the flux in transformer  110  goes from its maximum value in the positive direction to its maximum value in the negative direction (−Φ). In period T 3 , controller  124  controls switches S 1  and S 4  to close and switches S 2  and S 3  to open so that the voltage across primary coil  112  is again positive. During period T 3 , the flux in transformer  110  goes from its maximum negative value (−Φ) to its maximum positive value (Φ). During subsequent time periods T 4  and T 5 , the processes of time periods T 2  and T 3 , respectively, are repeated, while time period T 6  repeats the process of time period T 2 . Then, in time period T 7 , switches S 1  and S 4  are closed and switches S 2  and S 3  are open so that the voltage across primary coil  112  is again positive. During period T 7 , the flux in transformer  110  goes from its maximum negative value (−Φ) to zero. Then, in period T 8 , all switches S 1  to S 4  are open so there is no voltage across primary coil  112 , and any remaining flux in transformer  110  will decay during time period T 8 . 
     During second interval  204 , the open and closed positions of switches S 1  to S 4 , and the direction of both the voltage across primary coil  112  and the flux in transformer  110  are inverted from those of the corresponding time periods in the first interval. Note that during each interval, as shown in  FIG. 2C , the total duration of positive voltage across primary coil  112  is equal to the total duration of negative voltage across primary coil  112 . Additionally, in the exemplary graph of the flux in transformer  110  depicted in  FIG. 2D , the flux is zero at the start of each interval and zero during the last time period (e.g., T 8  and T 16 ). In other embodiments in which the total duration of positive voltage across primary coil  112  is not equal to the total duration of negative voltage across primary coil  112  (e.g., due to imperfections in controller  124 , switches S 1 -S 4  and/or for any other reason), time period T 8  may be set to allow the flux in transformer  110  to decay enough so that flux does not build up in the core each interval, potentially saturating the core. Note that in some embodiments the voltage during the last time period in each interval (e.g., time periods T 8  and T 16 ) need not be reduced to exactly zero; it only needs to be reduced enough so that the flux in transformer  110  decays enough to prevent transformer  110  from saturating the core during any interval. 
     Note that the first voltage pulse across primary coil  112  at the start of an interval (e.g., T 9 ) is in the opposite direction to the first voltage pulse (e.g., T 1 ) of the previous interval. Additionally, note that the first voltage pulse across primary coil  112  at the start of an interval (e.g., T 9 ) is in the opposite direction to the last voltage pulse (e.g., T 7 ) of the previous interval. In some embodiments, this helps to reduce the build-up of flux in transformer  110 . Furthermore, note that in the embodiment depicted in  FIGS. 2A-2D , the first pulse (e.g., T 1 ) and the last pulse (e.g., T 7 ) in an interval are one-half the width of each of the other pulses (e.g., T 2 -T 6 ) in the interval. 
     Note that the voltage across each arm of secondary coil  114  is determined by the voltage across primary coil  112  (e.g., as depicted in  FIG. 2C ) and the ratio of the turns in primary coil  112  and each arm of secondary coil  114 . This voltage passes alternately through diode  116  and diode  118  and onto capacitor  120  and output  122 . 
     Controller  124  may alter one or more parameters of the voltage across primary coil  112  during any portion of any interval, by varying one or more of the control parameters used to control H-bridge  108 , including but not limited to number of cycles per interval  206 , primary coil  112  dead-time  208  (e.g., T 8  and T 16 ), and cycle duration  210 . 
       FIG. 3A  depicts an exemplary graph of the variation of these three parameters by controller  124  when controlling the voltage across the primary coil vs. output power of the adapter in accordance with an embodiment. Initially, as more power is demanded from the adapter, controller  124  will reduce the duration of primary coil  112  dead-time  208  to generate more power. Eventually, as the power demand increases, number of cycles per interval  206  will begin to increase and then eventually plateau. Then, as the power demand continues to increase, cycle duration  210  will increase. This is depicted in more detail in  FIG. 3B . 
       FIG. 3B  depicts an exemplary graph of cycle frequency of the voltage across the primary coil of an adapter transformer vs. output power of the adapter in accordance with an embodiment. In some embodiments, at low power, controller  124  controls the cycle frequency at about 500,000 Hz. Then, as the power demand increases, the controller starts to reduce the cycle frequency, eventually reducing it to about 50,000 Hz. 
       FIGS. 4A and 4B  depict exemplary graphs of alternate control signals from controller  124  controlling, respectively, switches S 1  and S 4 , and switches S 2  and S 3  in H-bridge  108  in accordance with an embodiment.  FIG. 4C  depicts an exemplary graph of the voltage across primary coil  112  as a result of the switching signals depicted in  FIGS. 4A and 4B .  FIG. 4D  depicts an exemplary graph of the flux in transformer  110  due to the voltage across the coil depicted in  FIG. 4C  in accordance with an embodiment. 
     Note that for exemplary purposes only two intervals are depicted in each graph, first interval  402  and second interval  404 . Embodiments may include more or fewer intervals. First interval  402  includes time periods T 1  through T 7  and second interval  404  includes time periods T 8  through T 14 . 
     In time period T 1 , switches S 1  and S 4  are closed while switches S 2  and S 3  are open so that the voltage across primary coil  112  is positive as shown in  FIG. 4C . During time period T 1 , the flux in transformer  110  builds up from zero to its maximum (Φ). Then, in time period T 2 , controller  124  controls switches S 1  and S 4  to open and switches S 2  and S 3  to close so that the voltage across primary coil  112  is negative. During time period T 2 , the flux in transformer  110  goes from its maximum value in the positive direction to its maximum value in the negative direction (−Φ). In period T 3 , controller  124  controls switches S 1  and S 4  to close and switches S 2  and S 3  to open so that the voltage across primary coil  112  is again positive. During period T 3 , the flux in transformer  110  goes from its maximum negative value (−Φ) to its maximum positive value (Φ). During subsequent time periods T 4  and T 5 , the processes of time periods T 2  and T 3 , respectively, are repeated. Then, in time period T 6 , switches S 1  and S 4  are open and switches S 2  and S 3  are closed so that the voltage across primary coil  112  is negative, and the flux in transformer  110  goes from its maximum positive value (Φ) to zero. Then, in period T 7 , all switches S 1  to S 4  are open so there is no voltage across primary coil  112 , and any remaining flux in transformer  110  will decay during time period T 7 . 
     During second interval  404 , the open and closed positions of switches S 1  to S 4 , and the direction of both the voltage across primary coil  112  and the flux in transformer  110  are inverted from those of the corresponding time periods in the first interval. Note that during each interval, as shown in  FIG. 4C , the total duration of positive voltage across primary coil  112  is equal to the total duration of negative voltage across primary coil  112 . Additionally, in the exemplary graph of the flux in transformer  110  depicted in  FIG. 4D , the flux is zero at the start of each interval and zero during the last time period (e.g., T 7  and T 14 ). In other embodiments in which the total duration of positive voltage across primary coil  112  is not equal to the total duration of negative voltage across primary coil  112  (e.g., due to imperfections in controller  124 , switches S 1 -S 4  and/or for any other reason), time period T 7  may be set to allow the flux in transformer  110  to decay enough so that flux does not build up in the core each interval, potentially saturating the core. Note that in some embodiments the voltage during the last time period in each interval (e.g., time periods T 7  and T 14 ) need not be reduced to exactly zero; it only needs to be reduced enough so that the flux in transformer  110  decays enough to prevent transformer  110  from saturating the core during any interval. 
     The first voltage pulse across primary coil  112  at the start of an interval (e.g., T 8 ) is in the opposite direction to the first voltage pulse (e.g., T 1 ) of the previous interval. In some embodiments, this helps to reduce the build-up of flux in transformer  110 . Additionally, note that in the embodiment depicted in  FIGS. 4A-4D , the first pulse (e.g., T 1 ) and the last pulse (e.g., T 6 ) in an interval are one-half the width of each of the other pulses (e.g., T 2 -T 5 ) in the interval. 
     Note that controller  124  may alter one or more parameters of the voltage across primary coil  112  during any portion of any interval, by varying one or more of the control parameters used to control H-bridge  108 , including but not limited to number of cycles per interval  406 , primary coil  112  dead-time  408  (e.g., T 7  and T 14 ), and cycle duration  410 . Additionally, these parameters may be controlled by controller  124  as discussed above with respect to  FIGS. 3A and 3B . 
     Referring back to  FIG. 1 , the voltage pulses across primary coil  112  as discussed above induce voltage across secondary coil  114 . For example, a positive voltage across primary coil  112  induces a positive voltage in one arm of secondary coil  114  (e.g., between the center tap and diode  116 ), while a negative voltage across primary coil  112  induces a positive voltage in the other arm of secondary coil  114  (e.g., between the center tap and diode  118 ). The positive voltage from each arm passes through the respective diode and across capacitor  120  to output  122 . 
     Note that in embodiments in which a step-up converter is coupled after capacitor  120 , the step-up converter may be a boost converter, and may be controlled by controller  124  or by a separate controller. The step-up converter may be used to adjust the power factor of the adapter by, for example, stepping-up the voltage from secondary coil  114  to a value larger than the peak voltage output from secondary coil  114 . Additionally, note that in embodiments such as  FIG. 1  which include a transformer with a center tapped secondary coil, the voltage output from secondary coil  114  may be stepped-up as described in the U.S. patent application Ser. No. 13/568,414 entitled “Controlling an Adapter Transformer Voltage,” by Louis Luh and Eric Smith, which was filed on 7 Aug. 2012, which issued as U.S. Pat. No. 8,817,493 on 26 Aug. 2014, and which is hereby fully incorporated herein by reference. 
       FIG. 5  shows an embodiment similar to the one depicted in  FIG. 1 , but with inductor  502  placed between H-bridge  108  and primary coil  112 , and inductor  504  between the center tap of secondary coil  114  and ground. Inductor  502  may be any type of inductor and may be selected based on factors including but not limited to the desired switching characteristics of one or more switches in H-bridge  108 , such as soft switching for zero-voltage switching (ZVS). Inductor  504  may be any type of inductor and may be selected based on factors including but not limited to reducing a peak current present at diode  116  and/or diode  118 . The embodiment of  FIG. 5  operates similarly to the embodiment of  FIG. 1  as described above. Note that in some embodiments either inductor  502  or inductor  504  may be omitted. 
       FIG. 6  shows an embodiment similar to the one depicted in  FIG. 1 , with H-bridge  108  replaced by half H-bridge  602  and capacitor  604 , and controller  124  replaced by controller  606 . Half H-bridge  602  is any half H-bridge that includes two individual switches s 1  and s 2 , each of which is controlled by controller  606 . Half H-bridge  602  uses switches s 1  and s 2  in combination with capacitor  604  to control the voltage across primary coil  112  in transformer  110 . For example, when switch s 1  is closed and switch s 2  is open, the voltage from the top to the bottom of primary coil  112  is positive and capacitor  604  is charging; when switch s 1  is open and switch s 2  is closed, the voltage from the top to the bottom of primary coil  112  is negative and capacitor  604  is discharging; and when switch s 1  is open and switch s 2  is open there will be no voltage across primary coil  112 . Note that switches s 1  and s 2  can each be any type of switch implemented in any technology that can switch in response to a control signal. For example, switches s 1  and s 2  may include but are not limited to relays, or transistors such as FETs, including MOSFET transistors, and may be implemented using any combination of discrete and integrated components, and analog and/or digital technology. Note that capacitor  604  may be any capacitor selected based on factors including but not limited to the peak voltage from AC voltage  102 , the switching frequency of half H-bridge  602  as controlled by controller  606  and/or the output power of the adapter. 
     Controller  606  is a controller implemented in any combination of hardware and/or software and in any technology and may be implemented using the same or similar technology as controller  124 , and may include any combination of integrated and discrete components and may be implemented in any hardware module or apparatus. Controller  606  controls each switch s 1  and s 2  in half H-bridge  602  using similar processes and hardware as used by controller  124  to control, respectively, switches S 1  and S 4 , and switches S 2  and S 3  as described above. For example, referring to  FIGS. 2A and 2B , controller  606  may control switch s 1  based on the waveform of  FIG. 2A  and switch s 2  based on the waveform in  FIG. 2B  to generate the voltage waveform depicted in  FIG. 2C . 
       FIG. 7  shows an embodiment similar to the one depicted in  FIG. 6 , but with inductor  702  placed between half H-bridge  602  and primary coil  112 , and inductor  704  between the center tap of secondary coil  114  and ground. Inductor  702  may be any type of inductor and may be selected based on factors including but not limited to the desired switching characteristics of one or more switches in half H-bridge  602 , such as soft switching for zero-voltage switching (ZVS). Inductor  704  may be any type of inductor and may be selected based on factors including but not limited to reducing a peak current present at diode  116  and/or diode  118 . The embodiment of  FIG. 7  operates similarly to the embodiment of  FIG. 6  as described above. Note that in some embodiments either inductor  702  or inductor  704  may be omitted. 
       FIG. 8  depicts an embodiment similar to the one depicted in  FIG. 1 . Alternating current (AC) voltage  102  is coupled to rectifier  104  across capacitor  106  and into H-bridge  108 . Transformer  802  includes primary coil  804  and secondary coil  806 . Primary coil  804  is coupled to the output of H-bridge  108 , and secondary coil  806  is coupled through rectifier  808  across capacitor  120  to output  122 . As in the embodiment of  FIG. 1 , controller  124  is coupled to and controls switches S 1  through S 4  in H-bridge  108 . 
     Transformer  802  can be any transformer with a primary coil and a secondary coil implemented in any technology. The winding ratio of primary coil  804  to secondary coil  806  can be set to any value based on the input voltage and the desired output voltage. Transformer  802  may be a step-down transformer with a turns ratio between primary coil  804  and secondary coil  806  that may be set to any value based on AC voltage  102  and the desired voltage at output  120 . For example, in some embodiments, for an expected input voltage of 90 to 120 volts from AC voltage  102  and a desired output voltage in the range of 20 to 30 volts, a turns ratio between primary coil  804  and secondary coil  806  may be chosen to be about 4:1, while for an expected input voltage of 220 to 240 volts from AC voltage  102  for the same desired output voltage range, the turns ratio may be chosen to be about 8:1. In other embodiments, a turns ratio in the range of 4:1 up to 8:1 may be used. Additionally, as described above, in some embodiments a step-up converter is placed after capacitor  120  to step-up the voltage from secondary coil  806  through rectifier  808  based on a desired power factor of the adapter. In some embodiments, the step-up converter steps-up the voltage to between 40 volts and 50 volts, while in other embodiments, the voltage is stepped-up to a value less than 50 volts. 
     Rectifier  808  is a voltage rectifier that converts the positive and negative voltage output from secondary coil  806  into voltage that is going positive only. Rectifier  808  may include but is not limited to a full-bridge rectifier, a half-bridge rectifier, or any other rectifier that outputs only a positive-going voltage from an input that is positive and negative, and it may be implemented in any technology. 
     Note that the embodiment of  FIG. 8  operates similarly to the embodiment of  FIG. 1 . As discussed above with reference to  FIG. 1 , the alternating voltage input into primary coil  112  of transformer  110  (e.g., see  FIGS. 2C and 4C ) induces voltage in each arm of center tapped secondary coil  114  coupled to diode  116  and diode  118  and results in rectified voltage at capacitor  120 . In  FIG. 8  the voltage induced in secondary coil  806  as a result of controller  124  controlling switches S 1  to S 4  as depicted in  FIGS. 2A and 2B  and/or  4 A and  4 B results in a positive and negative going voltage across secondary coil  806  that is rectified by rectifier  808  and coupled across capacitor  120  to output  122   
     Note that in some embodiments an inductor may be coupled between H-bridge  108  and primary coil  804  similar to inductor  502  of  FIG. 5 . The inductor may be any type of inductor and may be selected based on factors including but not limited to the desired switching characteristics of one or more switches in H-bridge  108 , such as soft switching for ZVS. 
     In  FIG. 9 , AC voltage  102  is coupled to rectifier  104  across capacitor  106  and into the center tap of primary coil  904  of transformer  902 . Secondary coil  906  is coupled into rectifier  808  and across capacitor  120  to output  122 . The top end tap of primary coil  904  is coupled through switch  908  to ground and the bottom end tap of primary coil  904  is coupled through switch  910  to ground. Controller  912  is coupled to and controls switch  908  and switch  910 . 
     Transformer  902  can be any transformer with a center tapped primary coil and a secondary coil implemented in any technology. The winding ratio of each arm of primary coil  904  to secondary coil  906  can be set to any value based on the input voltage and the desired output voltage. Transformer  902  may be a step-down transformer with a turns ratio between each arm of primary coil  904  and secondary coil  906  that may be set to any value based on AC voltage  102  and the desired voltage at output  122 . For example, in some embodiments, for an expected input voltage of 90 to 120 volts from AC voltage  102  and a desired output voltage in the range of 20 to 30 volts, a turns ratio between each arm of primary coil  904  and secondary coil  906  may be chosen to be about 4:1, while for an expected input voltage of 220 to 240 volts from AC voltage  102  for the same desired output voltage range, the turns ratio may be chosen to be about 8:1. In other embodiments, a turns ratio in the range of 4:1 up to 8:1 may be used. Additionally, as discussed above, in some embodiments a step-up converter is placed after capacitor  120  to step-up the voltage from secondary coil  906  based on a desired power factor of the adapter. In some embodiments, the step-up converter steps-up the voltage to a value less than 50 volts, while in other embodiments, the voltage is stepped-up to between 40 volts and 50 volts. 
     Controller  912  controls switch  908  and switch  910  to control the voltage across each arm of primary coil  904  in transformer  902 . For example, when switch  908  is closed and switch  910  is open, the voltage from the center tap to the top of primary coil  904  is positive; when switch  908  is open and switch  910  is closed, the voltage from the center tap to the bottom of primary coil  904  is positive; and when both switch  908  and switch  910  are open, there is no voltage across either arm of primary coil  112 . Note that switch  908  and switch  910  can each be any type of switch implemented in any technology that can switch in response to a control signal. For example, switch  908  and switch  910  may include but are not limited to relays, or transistors (e.g., N-type) such as FETs, including MOSFET transistors, and may be implemented using any combination of discrete and integrated components, and analog and/or digital technology. 
     Controller  912  is a controller implemented in any combination of hardware and/or software and in any technology and may be configured and implemented similarly to controller  124 . Controller  912  may include any combination of integrated and discrete components and may be implemented in any hardware module or apparatus. Controller  912  controls switch  908  and switch  910  using similar processes and hardware as used by controller  124  to control, respectively, switches S 1  and S 4 , and switches S 2  and S 3  as described above. For example, referring to  FIGS. 2A and 2B , controller  912  may control switch  908  based on the waveform of  FIG. 2A  and switch  910  based on the waveform in  FIG. 2B  to generate the alternating polarity voltage waveform depicted in  FIG. 2C . 
     Controller  912  may be coupled to (not shown) and use input received from rectifier  104  and output  122  to control switch  908  and switch  910 . Note that the input to controller  912  from output  122  may include an isolation device or circuit (not shown) to electrically isolate the secondary side of transformer  902  from the primary side, and may also include a voltage divider (not shown) to reduce the feedback voltage from output  122  to controller  912 . 
     During operation, the alternating voltage across each arm of primary coil  904  induces an alternating polarity voltage across secondary coil  906  which is rectified in rectifier  508  and coupled to output  122  across capacitor  120 . Note that as discussed above, in some embodiments, a step-up converter may be coupled to the adapter in  FIG. 9  after capacitor  120 . 
     The embodiment of  FIG. 10  is similar to the embodiment of  FIG. 9  with inductor  1002  coupled between capacitor  106  and the center tap of primary coil  904 . Inductor  1002  may be any type of inductor and may be selected based on factors including but not limited to the desired switching characteristics of switch  908  and/or switch  910 , such as soft switching for ZVS. 
       FIG. 11  depicts an embodiment similar to the one depicted in  FIG. 9  with transformer  902  and rectifier  508  replaced by transformer  1102 , and diode  116  and diode  118 . AC voltage  102  is coupled to rectifier  104  across capacitor  106  and into the center tap of primary coil  1104  of transformer  1102 . Secondary coil  1106  has a center tap coupled to ground, and one end tap coupled through diode  116  across capacitor  120  to output  122 , and the other end tap coupled through diode  118  across capacitor  120  to output  122 . The top end tap of primary coil  1104  is coupled through switch  908  to ground and the bottom end tap of primary coil  1104  is coupled through switch  910  to ground. Controller  912  is coupled to and controls switch  908  and switch  910 . 
     Transformer  1102  can be any transformer with a center tapped primary coil and a center tapped secondary coil implemented in any technology. The winding ratio of each arm of primary coil  1104  to each arm of secondary coil  1106  can be set to any value based on the input voltage and the desired output voltage. Transformer  1102  may be a step-down transformer with a turns ratio between each arm of primary coil  1104  and each arm of secondary coil  1106  that may be set to any value based on AC voltage  102  and the desired voltage at output  122 . For example, in some embodiments, for an expected input voltage of 90 to 120 volts from AC voltage  102  and a desired output voltage in the range of 20 to 30 volts, a turns ratio between each arm of primary coil  1104  and each arm of secondary coil  1106  may be chosen to be about 4:1, while for an expected input voltage of 220 to 240 volts from AC voltage  102  for the same desired output voltage range, the turns ratio may be chosen to be about 8:1. In other embodiments, a turns ratio in the range of 4:1 up to 8:1 may be used. 
     Similar to the embodiment of  FIG. 9  as discussed above, controller  912  controls switch  908  and switch  910  to control the voltage across each arm of primary coil  1104  in transformer  1102 . For example, when switch  908  is closed and switch  910  is open, the voltage from the center tap to the top of primary coil  904  is positive; when switch  908  is open and switch  910  is closed, the voltage from the center tap to the bottom of primary coil  904  is positive; and when both switch  908  and switch  910  are open, there is no voltage across either arm of primary coil  1104 . 
     During operation, the alternating voltage across each arm of primary coil  1104  induces an alternating polarity voltage across each arm of secondary coil  1106 . For example, a positive voltage from the center tap of primary coil  1104  to the top end tap of primary coil  1104  (switch  908  closed and switch  910  open) induces a positive voltage in one arm of secondary coil  1106  (e.g., between the center tap and diode  116 ), while a positive voltage from the center tap of primary coil  1104  to the bottom end tap of primary coil  1104  (switch  908  open and switch  910  closed) induces a positive voltage in the other arm of secondary coil  1106  (e.g., between the center tap and diode  118 ). The positive voltage from each arm passes through the respective diode and across capacitor  120  to output  122 . Note that as discussed above, in some embodiments, a step-up converter may be coupled to the adapter in  FIG. 11  after capacitor  120 . 
       FIG. 12  shows an embodiment similar to the one depicted in  FIG. 11 , but with inductor  1202  placed between the top node of capacitor  106  and the center tap of primary coil  1104 , and inductor  1204  between the center tap of secondary coil  1106  and ground. Inductor  1202  may be any type of inductor and may be selected based on factors including but not limited to the desired switching characteristics of switch  908  and/or switch  910 , such as soft switching for zero-voltage switching (ZVS). Inductor  1204  may be any type of inductor and may be selected based on factors including but not limited to reducing a peak current present at diode  116  and/or diode  118 . The embodiment of  FIG. 12  operates similarly to the embodiment of  FIG. 11  as described above. Note that in some embodiments either inductor  1202  or inductor  1204  may be omitted. 
       FIG. 13  shows an adapter similar to the one depicted in  FIG. 1 , with the addition of inductor  1302  between the center tap of secondary coil  114  and ground, switch  1304  coupled between end tap  1306  and ground, switch  1308  coupled between end tap  1310  and ground, and controller  1312  coupled to and controlling H-bridge  108 , switch  1304  and switch  1308 . 
     Inductor  1302  can be any type of inductor implemented in any technology. The inductance of inductor  1302  can be selected based on parameters including the inductance of secondary coil  114 . In some embodiments, the ratio between the inductance of each arm of secondary coil  114  and the inductance of inductor  1302  is 5, 10 or in the range from 2 to 20. For example, in one embodiment, the inductance of one arm of secondary coil  114  is 100 microhenries and the inductance of inductor  1302  is selected to be 10 microhenries. 
     Switch  1304  and switch  1308  can each be any type of switch implemented in any technology that can switch in response to a control signal. For example, switch  1304  and/or switch  1308  may include but are not limited to relays, or transistors such as FETs, including MOSFET transistors, and may be implemented using any combination of discrete and integrated components, and analog and/or digital technology. Controller  1312  is similar to controller  124  and also includes control logic, programming and/or circuitry to control switch  1304  and switch  1308  as described below. 
     The embodiment of  FIG. 13  operates similarly to the embodiment of  FIG. 1 . Controller  1312  controls H-bridge  108  in the same manner as controller  124 . In addition, controller  1312  may control switch  1304  and switch  1308  to boost the voltage from secondary coil  114  as depicted in  FIGS. 14B and 14C  discussed below. 
       FIG. 14A  depicts an exemplary graph of the voltage across the primary coil  112  (similar to that depicted in  FIG. 2C  and  FIG. 4C ), and  FIGS. 14B and 14C  depict the relative timing of the control signals, respectively, for switch  1304  and switch  1308  from controller  1312  to boost the voltage from secondary coil  114 . As depicted in  FIG. 14A , during time period A 0  the voltage across primary coil  112  is positive. This induces a positive voltage in secondary coil  114  between the center tap and end tap  1306 . As depicted in  FIG. 14B , controller  1312  controls switch  1304  to remain closed during the first portion of time period A 0 ; then, during the second portion, controller  1312  controls switch  1304  to open, boosting the voltage from the top arm of secondary coil  114 . Controller  1312  may vary the portion of A 0  during which switch  1304  is open/closed in order to vary the magnitude of the voltage boost generated. Note that, as depicted in  FIG. 14C , controller  1312  controls switch  1308  to remain open during time period A 0 . 
     As depicted in  FIG. 14C , during time period A 1 , controller  1312  controls switch  1308  in a similar fashion to boost the voltage when the voltage across primary coil  112  is negative and the induced voltage in secondary coil  114  is positive from the center tap to end tap  1310  across the bottom arm of secondary coil  114 . Controller  1312  controls switch  1308  to remain closed during the first portion of time period A 1 ; then, during the second portion, controller  1312  controls switch  1308  to open, boosting the voltage from the bottom arm of secondary coil  114 . Note that as depicted in  FIG. 14B  controller  1312  controls switch  1304  to remain open during time period A 1 . Controller  1312  may vary the portion of A 1  during which switch  1308  is open/closed in order to vary the magnitude of the voltage boost generated. 
     Also note that if transformer  110  has the opposite polarity, then positive voltage is induced in the opposite arm of secondary coil  114  during time periods A 0  and A 1 , and the switching signals for switch  1304  and switch  1308  are interchanged. Additionally, if controller  1312  is not going to boost the voltage from transformer  110 , then controller  1312  controls switch  1304  and switch  1308  both to remain open 
     The foregoing descriptions of various embodiments have been presented only for purposes of illustration and description. They are not intended to be exhaustive or to limit the present invention to the forms disclosed. Accordingly, many modifications and variations will be apparent to practitioners skilled in the art. Additionally, the above disclosure is not intended to limit the present invention.

Metadata:
Filing Date: 20120808
Publication Date: 20150602
Grant Date: 20150602
Priority Date: 20120808
Inventors: LUH LOUIS
SMITH ERIC G.
Assignee: APPLE INC
CPC Classifications: [{"code": "H02M3/33576", "inventive": true, "first": true, "tree": "[]"}, {"code": "H02M3/33576", "inventive": true, "first": true, "tree": "[]"}, {"code": "H02M3/3376", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02M3/3376", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02M3/33576", "inventive": true, "first": true, "tree": "[]"}]
Family ID: 50066072