Abstract:
According to one aspect, embodiments of the invention provide a power supply system comprising an input line configured to receive input AC power, a rectifier having an input coupled to the input line and an output, a switch having a first end coupled to the output of the rectifier and a second end selectively coupled to an inductor, a capacitor coupled to the inductor, and control circuitry coupled to the inductor and the capacitor, wherein the control circuitry is configured to control the switch to selectively couple the output of the rectifier to the inductor to generate a first DC power level, operate in a first mode of operation while receiving the first DC power level, detect a phase angle of the rectified AC power, and transition into a second mode of operation in response to detection of the phase angle.

Description:
BACKGROUND OF INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    At least one example in accordance with the present invention relates generally to providing a low-voltage power supply to a low-power device. 
         [0003]    2. Discussion of Related Art 
         [0004]    In the home automation and energy efficiency market, the demand for “Smart Outlets” and other intelligent power products that are more cost and energy efficient is quickly growing. For example, such “Smart Outlets” may prevent the flow of energy to an outlet when it detects that a device coupled to the outlet has gone into standby mode. Additionally, a plurality of “Smart Outlets” may also be networked together to more efficiently control the distribution of power to the plurality of outlets. 
       SUMMARY OF THE INVENTION 
       [0005]    Aspects in accord with the present invention are directed to a power supply system comprising an input line configured to receive input AC power, a rectifier having an input coupled to the input line and an output, a switch having a first end coupled to the output of the rectifier and a second end selectively coupled to an inductor, a capacitor coupled to the inductor, and control circuitry coupled to the inductor and the capacitor, wherein the control circuitry is configured to control the switch to selectively couple the output of the rectifier to the inductor to generate a first DC power level, operate in a first mode of operation while receiving the first DC power level, detect a phase angle of the rectified AC power, and transition into a second mode of operation in response to detection of the phase angle. 
         [0006]    According to one embodiment, the control circuitry is further configured to operate in the second mode of operation while receiving a second DC power level from the capacitor. In another embodiment, the first mode of operation is an active mode of operation and the second mode of operation is a standby mode of operation, and wherein the first DC power level is greater than the second DC power level. 
         [0007]    According to another embodiment, the control circuitry includes a processor coupled to the inductor and the capacitor and a controller coupled to the switch and the capacitor. In one embodiment, the processor is configured to place selected processor tasks on hold in the standby mode of operation. In another embodiment, the power supply system further comprises a zero-crossing flag line coupled to the processor and configured to detect the phase angle of the rectified AC power. In another embodiment, the switch is controlled by the controller to selectively couple the output of the rectifier to the inductor to provide voltage pulses to the inductor. 
         [0008]    According to one embodiment, the switch is a Field Effect Transistor. In one embodiment, the switch is operated by the control circuitry at a switching frequency in the range of 5 MHz-20 MHz. In another embodiment, the inductor has a value in the range of 10 uH-500 uH. In one embodiment, the capacitor has a value in the range of 1 nF to 10 μF. 
         [0009]    According to one embodiment, the rectifier, switch, inductor, and control circuitry are integrated within a single chip. 
         [0010]    Another aspects in accord with the present invention is directed to a method for providing DC power to a processor coupled to an AC input line, the method comprising receiving input AC power from an AC power source coupled to the AC input line, rectifying the input AC power to generate rectified AC power, generating a first DC power level from the rectified AC power by selectively coupling the rectified AC power to an inductor, providing the first DC power level to a capacitor and the processor and operating the processor in a first mode of operation, detecting a phase angle of the rectified AC power, and transitioning the processor into a second mode of operation in response to detection of the phase angle. 
         [0011]    According to one embodiment, transitioning the processor into a second mode of operation includes transitioning the processor into a standby mode of operation and discharging the capacitor to provide, in the second mode of operation, a second DC power level to the processor which is less than the first DC power level. In one embodiment, the method further comprises placing selected processor tasks on hold while the processor is in the standby mode of operation. 
         [0012]    According to another embodiment, detecting includes monitoring a zero crossing flag line coupled to the processor and determining a zero-crossing window corresponding to a phase angle range of the rectified AC power that includes a phase angle at which the rectified AC power has a zero voltage value. In one embodiment, the method further comprises transitioning the processor into the first mode of operation in response to a determination that the zero-crossing window has passed. 
         [0013]    According to one embodiment, generating includes selectively coupling the rectified AC power to the inductor using a control signal having a fixed frequency and a duty cycle that varies with variations in the phase angle. In one embodiment, selectively coupling the rectified AC power to the inductor includes controlling the switch using the control signal to provide voltage pulses to the inductor from the rectified AC power. 
         [0014]    Aspects in accord with the present invention are also directed to a processor system comprising an input line configured to receive input AC power, the input AC power having a cyclical waveform including a portion at which a voltage of the waveform is less than a threshold voltage, a processor configured to operate from DC power derived from the input AC power, and means for detecting the voltage of the waveform, and controlling the processor to operate in a first mode of operation upon detection that the voltage is greater than the voltage threshold and for operating in a second mode of operation upon detection that the voltage is equal to or less than the voltage threshold. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0015]    The accompanying drawings are not intended to be drawn to scale. In the drawings, each identical or nearly identical component that is illustrated in various FIGs. is represented by a like numeral. For purposes of clarity, not every component may be labeled in every drawing. In the drawings: 
           [0016]      FIG. 1  is a circuit diagram illustrating a power supply system in accordance with aspects of the present invention; 
           [0017]      FIG. 2  is a graph illustrating a rectified signal and corresponding voltage pulses in accordance with aspects of the present invention; and 
           [0018]      FIG. 3  is a flow chart illustrating a process for providing low DC supply voltage from AC mains in accordance with aspects of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0019]    Embodiments of the invention are not limited to the details of construction and the arrangement of components set forth in the following description or illustrated in the drawings. Embodiments of the invention are capable of being practiced or of being carried out in various ways. Also, the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” or “having,” “containing”, “involving”, and variations thereof herein, is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. 
         [0020]    As discussed above, “Smart Outlets” and other intelligent power products are commonly used to improve cost and efficiency. A “Smart Outlet” often includes an embedded processor which is configured to monitor and control the outlet. The embedded processor is typically coupled to AC mains which provides power to the outlet. However, running the embedded processor off of the AC line while minimizing the impact on the power provided to the outlet may require that the embedded processor be a low-power processor. For example, an embedded low-power processor may receive a low supply voltage from a low-voltage power supply coupled to the AC line. Generating such a low-voltage supply from the AC line typically calls for the use of a high-voltage input capacitor and a high-capacitance output capacitor within the low-voltage supply, both of which are relatively large. The low-voltage power supply may also include additional components (e.g., diodes, inductors, a controller Integrated Circuit (IC), transistors, resistors, capacitors, etc.) which also occupy valuable space and cause the supply to be expensive. 
         [0021]    At least some embodiments described herein provide a lower-cost and smaller-size low-voltage power supply design that may eliminate the need for an input capacitor and reduce the size of other components within the power supply. 
         [0022]      FIG. 1  is a circuit diagram of a power supply system  102  in accordance with one embodiment. The power supply system  102  is coupled to the AC line and neutral inputs  101 ,  103  and includes control circuitry which is configured to operate the power supply system  102 . In one embodiment, the control circuitry includes a processor  116  and a switch controller  107 . 
         [0023]    The power supply system  102  also includes a bridge rectifier  104 . The bridge rectifier  104  is coupled to the AC line  101  and neutral line  103  inputs and includes a plurality of diodes (first  104   a,  second  104   d,  third  104   g,  and fourth  104   j ). The anode  104   c  of the first diode  104   a  and the cathode  104   e  of the second diode  104   d  are both coupled to the AC line input  101 . The anode  104   k  of the fourth diode  104   j  and the cathode  104   i  of the third diode  104   g  are both coupled to the AC neutral line  103 . The anode  104   f  of the second diode  104   d  and the anode  104   h  of the third diode  104   g  are both coupled to the processor  116  via a negative supply line  115 . The cathode  104   b  of the first diode  104   a  and the cathode  1041  of the fourth diode  105   j  are both coupled to a switch  106 . 
         [0024]    The switch  106  is also coupled to an input  113  of an inductor  112  and the switch controller  107 . According to one embodiment, the switch  106  is a single high speed, high voltage transistor (e.g., a Field-Effect Transistor (FET)). However in other embodiments, the switch  106  may be any other type of high speed, high voltage transistor (e.g., a Gallium Nitride transistor or a Silicon Carbide transistor). Also in other embodiments, any number of high speed, high voltage transistors may be utilized in the switch  106 . 
         [0025]    The switch controller  107  is coupled to the negative supply line  115  and to the cathode  104   b  of the first diode  104   a.  The switch controller  107  is also coupled to the positive supply line  117  via a feedback line  119 . According to one embodiment, the switch controller  107  includes a comparator. 
         [0026]    An output  118  of the inductor  112  is coupled to the processor  116  via a positive supply line  117 . According to one embodiment, the inductor  112  is relatively small. For example, in one embodiment, the inductor  112  has a value of 100 uH (assuming a clock speed of &gt;10 MHz). However, in other embodiments, the inductor  112  may be of any appropriate size. 
         [0027]    According to one embodiment, the processor  116  is a low-power processor. For example, in one embodiment, the processor  116  has power requirements of 2.0-3.6V, an active current requirement of about 10 mA and a standby (or sleep) current requirement of about 1 μA. However, in other embodiments, the processor  116  may have different power requirements. 
         [0028]    A fifth diode  108  is coupled across the power supply system  102 . The cathode  109  of the fifth diode  108  is coupled to the switch  106  and the input  113  of the inductor  112  and the anode  111  of the fifth diode  111  is coupled to the negative supply line  115 . 
         [0029]    An output capacitor  110  is coupled between the positive supply line  117  and the negative supply line  115 . According to one embodiment, the output capacitor  110  is relatively small. For example, in one embodiment, the output capacitor  110  has a value of about 5 nF. However, in other embodiments, the output capacitor  110  may be of any appropriate size. 
         [0030]    According to one embodiment, the power supply system  102  also includes a zero-crossing flag line  114  which is coupled between the switch  106  and the processor  116 . 
         [0031]    AC power provided to the bridge rectifier  104 , via the AC line input  101 , is rectified and full-wave rectified power is provided to the switch  106 . According to one embodiment, the voltage received by the switch  106  from the AC line input  101  via the bridge rectifier  104  ranges from 0V to 354V. To drop a relatively high voltage (e.g., 354V) to a level appropriate for the low-power processor  116  (e.g., to 3.3 VDC), the switch  106  is opened and closed by the switch controller  107 , based on the voltage on the positive supply line  117  sensed via the feedback line  119 , to drive the inductor  112  to provide the appropriate level of voltage to the processor  116 . 
         [0032]    When the switch  106  is closed, voltage from the switch  106  (i.e. from the received rectified power) drives the inductor  112  to charge the capacitor  110  and provide voltage to the positive supply line  117  of the processor  116 . As the inductor  112  is relatively small (e.g., 100 uH), to avoid inductor saturation the switch  106  is opened and closed rapidly by the switch controller  107  to produce narrow voltage pulses (i.e. narrow portions of the rectified power received by the switch  106 ). The narrow voltage pulses drive the inductor  112  for short periods of time, producing the desired voltage on the positive supply line  117  to power the processor  116 , while preventing inductor saturation. 
         [0033]    When the switch  106  is opened, the voltage at the input  113  of the inductor  113  moves negative until the fifth diode  108  turns on and the energy previously stored on the inductor  112  is provided to the output capacitor  110 . According to one embodiment, as the processor  116  continuously draws power from the output capacitor  110 , the supply voltage may sag. As the values of the inductor  112  and output capacitor  110  are relatively small, the storage capacities of the inductor  112  and output capacitor  110  may be limited. Thus, near the zero-crossing of the rectified power received by the switch  106 , when the voltage pulses provided from the switch  106  to the inductor  112  go to zero, the energy stored on the inductor  112  and the output capacitor  110  may not be at a sufficient level to fully power the processor  116  alone (e.g., at 3.3 VDC and 10 mA). As a result, certain processor tasks may potentially be interrupted. 
         [0034]    According to one embodiment, to avoid the interruption of processor tasks when energy stored on the inductor  112  and output capacitor  110  is insufficient to fully power the processor  116  in an active state (i.e. around the zero-crossing of the rectified power received by the switch  106 ), the processor  116  monitors the received rectified power at the switch  106  for approaching zero-crossings (e.g., via the zero-crossing flag line  114 ). For example, in one embodiment, the processor  116  determines a phase angle at which a zero-crossing of the rectified power is approaching. The processor  116  then monitors the rectified power (e.g., via the zero-crossing flag line  114 ) for that phase angle (i.e., the phase angle indicating to the processor  116  that a zero-crossing of the rectified power is approaching). The indication of an approaching zero-crossing does not necessarily mean that the rectified power has or will cross zero, but only that the rectified power is approaching, or has reached, zero. In other embodiments, any appropriate method for identifying an approaching zero-crossing may be utilized. 
         [0035]    When the processor  116  senses an approaching zero-crossing, the processor  116  transitions to a standby (or sleep) state until the zero-crossing window (i.e., when the zero-crossing is present) has passed. By entering a standby state, the processor requires a lower amount of power (than the active state) to maintain the state of the processor  116  and the lower amount of power may be successfully supplied by the output capacitor  110  and the inductor  112  around the zero-crossings. While the processor  116  is in a standby state (i.e. during the zero-crossing window), certain processor tasks which cannot be interrupted (e.g., radio communications or sensor readings) are put on hold until the zero-crossing window has passed. 
         [0036]    For example, while operating in an active state, the processor  116  monitors the received rectified power at the switch  106  for approaching zero-crossings. Upon sensing an approaching zero crossing via the zero-crossing flag line  114 , the processor  116  transitions to a standby (or sleep) state to avoid interruption of a processor task. According to one embodiment, in the standby state the processor  116  requires 1 μA and at least 2V to maintain the state of the processor during the zero-crossing window (as apposed to 10 mA and 3.3V when the processor is in an active state). In one embodiment, an output capacitor  110  of 5 nF has sufficient capacity (charged while the processor  116  is in an active state) to maintain the state of the processor  116 , when the processor  116  is in a standby state, with only 34 mV of voltage sag and at 50 Hz, the zero-crossing time is about 170 uS. 
         [0037]    In other embodiments, where the standby and/or active power requirements of the processor are different, the values of the output capacitor  110  and inductor  112  may be designed differently to provide the appropriate storage capacity capable of powering the processor  116  in standby mode during a zero-crossing window. 
         [0038]    Once the processor  116  determines that the zero-crossing window has passed, the processor  116  is powered into an active state with power from the inductor  112  (driven by voltage pulses from the switch  106 ). In one embodiment, the zero-crossing window (i.e. when the processor  116  is in standby mode and unable to perform certain tasks) is 170 μS (i.e. about 3 degrees wide out of a 180 degree line cycle or 1.7% of the entire line cycle); however, in other embodiments, the zero-crossing window may be different depending on the rectified power provided to the switch  106 . In one embodiment, the task window (i.e. the period in which the processor can perform tasks without interruption) is 10 mS. 
         [0039]    According to one embodiment, certain processor tasks are unable to be fully performed within the designated task window. For example, certain wireless personal area network implementations (i.e. technology utilizing the IEEE 802.15.4 standard such as ZigBee) may require more than the exemplary 10 mS task window discussed above. For instance, according to one embodiment, a ZigBee communication may be performed in 5 mS, but initial network joining requires 15 mS. In such a situation, techniques for granularizing the network join process (i.e. spreading the process over multiple task windows) may be utilized to prevent the sudden interruption of the process. 
         [0040]      FIG. 2  is a graph  200  illustrating one embodiment of the rectified power  202  received by the switch  106  and voltage pulses  204  generated by the switch  106  from the rectified power  202  and provided to the inductor  112  to drive the inductor  112 . The full-wave rectified power  202  is generated by the bridge rectifier  104  from an AC signal received from the AC line input  101  and provided to the switch  106 . 
         [0041]    As the switch  106  is opened and closed rapidly, for example at 10 MHz or greater, portions of the rectified power  202  (i.e. voltage pulses  204 ) are provided to the inductor  112 . Near the peak  206  of the rectified power  202 , the voltage pulses  204  are at their narrowest width as the rectified power  202  is at its greatest magnitude and only a small portion of the rectified power  202  is necessary to drive the inductor  112  to provide the necessary power to the processor  116 . However, as the rectified power  202  moves towards its minimum value  208  (i.e. towards a zero-crossing  210 ); the voltage pulses  204  become wider as the rectified power  202  moves to zero and a larger portion of the rectified power  202  is required to drive the inductor  112  to provide the necessary power to the processor  116 . 
         [0042]    The processor  116  monitors the rectified power  202  for approaching zero-crossings via the zero crossing flag line  114  as discussed above. At the zero crossing  210 , the voltage pulses  204  go to zero as the rectified power  202  also goes to zero. Therefore, as a zero-crossing  210  approaches the processor transitions to standby mode and is maintained in standby mode by power previously stored on the output capacitor  110  and the inductor  112 . When the processor  116  determines that the zero-crossing window has passed, the processor  116  transitions back to active mode and is powered by the inductor  112  which is again driven by the voltage pulses  204 . 
         [0043]      FIG. 3  is a flow chart illustrating a process  300  for providing a low supply voltage from AC mains with the power supply system  102 . At block  302 , the power supply system  102  receives AC power from the AC line input  101  and the neutral line input  103 . At block  304 , the full-bridge rectifier  104  rectifies the received AC power and generates full-wave rectified AC power. 
         [0044]    At block  306 , the switch  106  is closed and a portion of the full-wave rectified AC power (i.e. a voltage pulse) is provided to the inductor  112 . At block  308 , the inductor  112  is driven by the portion of the rectified power received from the switch  106  to provide a voltage to the processor  116 . At substantially the same time, at block  310 , the inductor  112  is also driven by the portion of the rectified power received from the switch  106  to provide a voltage to the output capacitor  110 , thereby charging the output capacitor  110 . 
         [0045]    At block  312 , the switch  106  is opened and the voltage pulse provided to the inductor  112  goes to zero. At block  314 , the energy stored on the inductor  112  and the output capacitor  110  is provided to the processor  116 . At block  306 , the switch  106  is again closed. As discussed above, the switching frequency of the regulator is relatively high such that blocks  306  to  314  are performed relatively quickly so as to avoid saturation of the relatively small inductor  112  and so that the inductor  112  provides the appropriate level of voltage to the processor  116 . 
         [0046]    At block  316 , once the inductor  112  is driven to provide power to the processor  116 , the processor is powered into an active state. At block  318 , while being powered by voltage from the inductor  112 , the processor  115  monitors the rectified power at the switch  106 . At block  320 , a determination is made whether a zero-crossing of the rectified power is approaching. In response to a determination that a zero-crossing is not present, at block  316  the processor  116  remains in the active state and at block  318  continues to monitor the rectified power for approaching zero-crossings. In response to the identification of an approaching zero-crossing, at block  322  the processor  116  enters a standby (or sleep) state. As discussed above, during the standby state, the lower power requirements of the processor are met by the output capacitor  110  and the inductor  112 . Also during the standby state, certain processor tasks which cannot be interrupted are put on hold until the zero-crossing window has passed. 
         [0047]    At block  320 , a determination is made whether a zero-crossing window of the rectified power has passed. In response to a determination that a zero-crossing is not present, at block  316  the processor  116  transitions back to the active state and at block  318  continues to monitor the rectified power for zero-crossings. In response to a determination that a zero-crossing is still present, at blocks  318  and  320  the processor  116  is maintained in the standby state and continues to monitor the rectified power for the end of the zero-crossing window. 
         [0048]    According to one embodiment, due to the elimination of the input capacitor and the reduction in size of other components (e.g., the output capacitor  110  and the inductor  112 ) within the power supply, the entire power supply system  102  is integrated onto a single chip. In another embodiment, due the reduced size of the power supply system  102 , the power supply system  102  is combined with other application-specific circuitry onto a single chip. For example, the power supply system  102  and additional application-specific circuitry (e.g., linear hall-effect current sensors, voltage measurement, power switches, digital hall-effect sensors, antennas, etc.) may all be included within a single chip of a “Smart Outlet.” 
         [0049]    As described herein, the switch  106  is a high speed, high voltage switch; however, in other embodiments, any type of switch  106  capable of driving the inductor  112  to provide the appropriate level of voltage to the processor  116  may be utilized. 
         [0050]    As also described herein, the power supply system  102  is described in relation to intelligent power products; however, in other embodiments, the power supply system  102  may be utilized wherever a power supply is desired to supply a device with a low voltage from AC mains. 
         [0051]    As described herein, the power supply system  102  includes a bridge rectifier  104  capable of full-wave rectification; however, in other embodiments, any other type of rectifier (e.g., a half-wave rectifier) may be utilized and the processor may be configured to account for the corresponding zero-crossing and task windows. 
         [0052]    As described herein, the power supply system  102  provides low level power to a processor; however, in other embodiments, the power supply system  102  may be configured to provide low level power to any low power device. 
         [0053]    As also described herein, the control circuitry of the power supply system  102  includes the processor  116  and the switch controller  107 ; however, in other embodiments, the control circuitry of the power supply system  102  may only include the processor  116 . In such an embodiment, the processor  116  would control the switch  106 , rather than the switch controller  107 , to drive the inductor  112  to provide the appropriate voltage to the processor  116 . 
         [0054]    As described herein, by utilizing a switch to drive an inductor, the power supply system  102  is able to drop a high AC mains input voltage down to a relatively low voltage supply level, absent the use of a large input capacitor. In addition, by utilizing a low duty cycle switching regulator (e.g. 5%), the size of certain components (e.g., the output capacitor and the inductor) within the power supply system  102  may be reduced. Finally, by having a processor coupled to the power supply system  102  enter standby mode upon detecting an approaching zero-crossing, the power supply system  102  may be able to prevent processor task interruption due to reduced energy storage capacity. 
         [0055]    Having thus described several aspects of at least one embodiment of this invention, it is to be appreciated various alterations, modifications, and improvements will readily occur to those skilled in the art. Such alterations, modifications, and improvements are intended to be part of this disclosure, and are intended to be within the spirit and scope of the invention. Accordingly, the foregoing description and drawings are by way of example only.