Patent Publication Number: US-11664654-B2

Title: Input overvoltage protection circuits for power supplies

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of and priority to U.S. application Ser. No. 16/737,403 filed Jan. 8, 2020, and issued as U.S. Pat. No. 11,258,248 on Feb. 22, 2022. The entire disclosure of the above application is incorporated herein by reference. 
     TECHNICAL FIELD 
     The present disclosure relates to input overvoltage protection circuits for power supplies. 
     BACKGROUND 
     This section provides background information related to the present disclosure which is not necessarily prior art. 
     Electrical power supplies include power circuits receiving power from input power sources. Sometimes, the power supplies include circuitry coupled between the power sources and the power circuits for providing input overvoltage and/or inrush current protection. For example, the power supplies may include one or more electromechanical switching devices coupled between the power sources and the power circuits to disconnect the power circuits during an overvoltage condition. In other examples, resistors may be coupled across the electromechanical switching devices to limit input inrush current from the power sources. 
     SUMMARY 
     This section provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features. 
     According to one aspect of the present disclosure, an electrical power supply includes a power converter, a protection circuit, and a control circuit. The protection circuit includes an input coupled to an electrical power source for receiving an input voltage, an output coupled to the power converter for providing an output voltage to the power converter, a first switching device coupled in a current path between the input and the output, and a second switching device coupled across the first switching device. The first switching device is controllable to turn on during startup of the power converter. The control circuit is in communication with the first switching device and the second switching device. The control circuit is configured to sense the input voltage and the output voltage, in response to the output voltage exceeding a first defined threshold, turn off the first switching device and turn on the second switching device to supply power to the power converter, and in response to the input voltage exceeding a second defined threshold, turn off the second switching device to disconnect the electrical power source from the power converter. 
     According to another aspect of the present disclosure, a protection circuit for coupling between an electrical power source and a power converter to provide input overvoltage protection for the power converter is disclosed. The protection circuit includes an input configured to couple to an electrical power source for receiving an input voltage, an output configured to couple to the power converter for providing an output voltage to the power converter, a first switching device coupled in a current path between the input and the output, a second switching device coupled across the first switching device, and a control circuit. The first switching device is controllable to turn on during startup of the power converter. The control circuit is in communication with the first switching device and the second switching device. The control circuit is configured to sense the input voltage and the output voltage, in response to the output voltage exceeding a first defined threshold, turn off the first switching device and turn on the second switching device to supply power to the power converter, and in response to the input voltage exceeding a second defined threshold, turn off the second switching device to disconnect the electrical power source from the power converter. 
     Further aspects and areas of applicability will become apparent from the description provided herein. It should be understood that various aspects of this disclosure may be implemented individually or in combination with one or more other aspects. It should also be understood that the description and specific examples herein are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations, and are not intended to limit the scope of the present disclosure. 
         FIG.  1    is a block diagram of a protection circuit including two switching devices for disconnecting a power source from a power converter according to one example embodiment of the present disclosure. 
         FIG.  2    is a schematic diagram of a power supply including a power source, a power converter, and a protection circuit having a MOSFET, a relay and a control circuit for controlling the MOSFET and the relay to disconnect the power source from the power converter according to another example embodiment. 
         FIG.  3    is a block diagram of a portion of the control circuit of  FIG.  2   . 
         FIG.  4    is a timing diagram including waveforms of different parameters from the power supply of  FIG.  2   . 
         FIG.  5    is a schematic diagram of a power supply including a protection circuit having a switching device to limit inrush input current according to another example embodiment. 
         FIG.  6    is a schematic diagram of a power supply including a protection circuit having a resistor to limit inrush input current according to yet another example embodiment. 
         FIG.  7    is a schematic diagram of a power supply including a protection circuit having a switching device controlled with an auxiliary source according to another example embodiment. 
         FIG.  8    is a schematic diagram of a power supply including a power source, a power converter, and a protection circuit coupled in a low-side rail between the power source and the power converter according to yet another example embodiment. 
         FIG.  9    is a schematic diagram of a power supply including a DC power source, a DC/DC power converter, and a protection circuit for disconnecting the DC power source from the DC/DC power converter according to another example embodiment. 
     
    
    
     Corresponding reference numerals indicate corresponding (but not necessarily identical) parts and/or features throughout the several views of the drawings. 
     DETAILED DESCRIPTION 
     Example embodiments are provided so that this disclosure will be thorough, and will fully convey the scope to those who are skilled in the art. Numerous specific details are set forth such as examples of specific components, devices, and methods, to provide a thorough understanding of embodiments of the present disclosure. It will be apparent to those skilled in the art that specific details need not be employed, that example embodiments may be embodied in many different forms and that neither should be construed to limit the scope of the disclosure. In some example embodiments, well-known processes, well-known device structures, and well-known technologies are not described in detail. 
     The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting. As used herein, the singular forms “a,” “an,” and “the” may be intended to include the plural forms as well, unless the context clearly indicates otherwise. The terms “comprises,” “comprising,” “including,” and “having,” are inclusive and therefore specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. The method steps, processes, and operations described herein are not to be construed as necessarily requiring their performance in the particular order discussed or illustrated, unless specifically identified as an order of performance. It is also to be understood that additional or alternative steps may be employed. 
     Although the terms first, second, third, etc. may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms may be only used to distinguish one element, component, region, layer or section from another region, layer or section. Terms such as “first,” “second,” and other numerical terms when used herein do not imply a sequence or order unless clearly indicated by the context. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the example embodiments. 
     Spatially relative terms, such as “inner,” “outer,” “beneath,” “below,” “lower,” “above,” “upper,” and the like, may be used herein for ease of description to describe one element or feature&#39;s relationship to another element(s) or feature(s) as illustrated in the figures. Spatially relative terms may be intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as “below” or “beneath” other elements or features would then be oriented “above” the other elements or features. Thus, the example term “below” can encompass both an orientation of above and below. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly. 
     Example embodiments will now be described more fully with reference to the accompanying drawings. 
     A protection circuit for coupling between an electrical power source and a power converter to provide input overvoltage protection for the power converter according to one example embodiment of the present disclosure is illustrated in  FIG.  1    and indicated generally by reference number  100 . As shown in  FIG.  1   , the protection circuit  100  includes an input  102  for coupling to an electrical power source (not shown) to receive an input voltage Vin, an output  104  for coupling to a power converter (not shown) to provide an output voltage Vout to the power converter, two switching devices  106 ,  108 , and a control circuit  110  in communication with the switching devices  106 ,  108 . The switching device  106  is coupled in a current path between the input  102  and the output  104 , and controllable to turn on during startup of the power converter. The switching device  108  is coupled across the switching device  106 . The control circuit  110  is configured to sense the input voltage Vin and the output voltage Vout, turn off the switching device  106  and turn on the switching device  108  to supply power to the power converter in response to the output voltage Vout exceeding a defined output voltage threshold, and turn off the switching device  108  to disconnect the power source from the power converter in response to the input voltage Vin exceeding a defined input voltage threshold. 
     As such, by employing the protection circuit  100  and/or any other protection circuit disclosed herein to disconnect the power source from the power converter, overvoltage protection from excessive input voltage is provided for the power converter. This may be particularly useful in applications (e.g., outdoor applications, etc.) requiring excessive overvoltage protection such as at least 150% of the rated input voltage. 
     As explained above, the switching device  106  is turned on (e.g., closed position) during startup of the power converter. During this time, the switching device  108  is initially turned off (e.g., open position). As a result, current from the input power source may be passed to the power converter via the switching device  106  to, for example, charge an effective capacitance of the power converter. After the effective capacitance is sufficiently charged, the control circuit  110  turns off the switching device  106  and turns on the switching device  108 . 
     The capacitances of the power converter may be sufficiently charged when the output voltage Vout reaches the defined output voltage threshold. For example, and as shown in  FIG.  1   , the protection circuit includes an output sensor  114  such as a resistive voltage sensor, etc. coupled across the output  104 . The control circuit  110  receives a signal from the output sensor  114  representing the output voltage Vout. In response to the control circuit  110  determining the output voltage Vout has reached the defined output voltage threshold, the control circuit  110  may send a control signal to the switching device  106  to open the switching device  106 , and a control signal to the switching device  108  to close the switching device  108 . At this time, power is supplied from the power source to the power converter via the closed switching device  108 . 
     In such examples, the output voltage defined threshold may be equivalent to a rated peak voltage of the input voltage Vin. As such, if the input voltage Vin is an AC input voltage, the output voltage defined threshold may be equal to the rated peak voltage of the AC input voltage. In such examples, the output voltage defined threshold may be 85V, 120V, 220V, 250V, 275V, 300V, etc. 
     If the input voltage Vin exceeds the defined input voltage threshold, the switching device  108  is turned off. For example, and as shown in  FIG.  1   , the protection circuit includes an input sensor  112  such as a resistive voltage sensor, etc. coupled across the input  102 . In such examples, the control circuit  110  receives a signal from the sensor  112  representing the input voltage Vin. In response to the control circuit  110  determining the input voltage Vin has reached the defined input voltage threshold, the control circuit  110  may send a control signal to the switching device  108  to open the switching device  108 . At this time, the switching device  108  and the switching device  106  are open thereby disconnecting the power converter from the power source providing an excessive input voltage. 
     The defined input voltage threshold may be any suitable value above the rated peak voltage of the input voltage Vin. For instance, the defined input voltage threshold may be a set value higher than the rated peak voltage of the power source. For example, if the input voltage Vin is an AC input voltage, the input voltage defined threshold may be equal to a voltage at least 120% of the rated peak voltage of the AC input voltage. In such examples, if the rated peak voltage of the AC input voltage is 275V, the input voltage threshold may be set to 330V (e.g., 275V*1.2). In other examples, the input voltage defined threshold may be equal to a voltage at least 150%, at least 173%, etc. of the rated peak voltage of the AC input voltage. 
     In other examples, the switching device  108  may be turned off when the input voltage Vin exceeds the defined input voltage threshold for a defined period of time. This may be useful when the power converter is able to withstand momentary spikes in the input voltage. In such examples, the defined period of time may be based on the defined input voltage threshold. For example, if the input voltage threshold is set to a high value (e.g., 173% of the rated peak voltage of the input voltage), the defined period of time may be set to a short time period (e.g., 200 milliseconds, etc.). If the input voltage threshold is instead set to a lower value (e.g., 150% of the rated peak voltage of the input voltage), the defined period of time may be set to a longer time period (e.g., 5 seconds, etc.). 
     Additionally, the switching device  108  may be turned off based on a bulk output voltage across the capacitance. For example, if the rated peak voltage of the AC input voltage is 275V, the bulk output voltage across the capacitance may reach 396V during normal operation. In such examples, the switching device  108  may be turned off if the bulk output voltage exceeds 560V for 1 millisecond, 540V for 50 milliseconds, 500V for 5 seconds, etc. 
     In some examples, the control circuit  110  may control the switching device  106  to turn on during startup of the power converter. For example, and as explained above, the control circuit  110  may send a control signal to the switching device  106  to close the switching device when the power converter is enabled (e.g., during startup of the power converter, etc.). In other examples, and as further explained below, the switching device  106  may be turned on based on an auxiliary supply, the input voltage, etc. 
     For example,  FIG.  2    illustrates a power supply  200  including a protection circuit  202  having a self-biasing switching device. Specifically, the power supply  200  includes the protection circuit  202  having a self-biasing MOSFET Q 1  and a relay K 1 , a power circuit  218  receiving power from an AC power source  216  via the protection circuit  202 , an input voltage sensor  212 , an output voltage sensor  214 , and a control circuit  210 . As shown, the power converter  218  includes an AC/DC power factor correction (PFC) circuit  220  and a DC/DC power conversion circuit  222  coupled between the PFC circuit  220  and a load. 
     The MOSFET Q 1  and the relay K 1  of the protection circuit  202  may be similar to the switching devices  106 ,  108  of  FIG.  1   . For example, and as shown in  FIG.  2   , the MOSFET Q 1  is coupled in a current path between an input of the protection circuit  202  (e.g., the power source  216 ) and an output of the protection circuit  202  (e.g., the power converter  218 ), and the relay K 1  is coupled across the MOSFET Q 1 . 
     As explained above, the MOSFET Q 1  of protection circuit  202  is self-biasing. For example, the MOSFET Q 1  of  FIG.  2    may be self-biased in response to an input voltage from the power source  216 . Specifically, and as shown in  FIG.  2   , the protection circuit  202  includes a resistor R 1  coupled between a drain terminal and a gate terminal of the MOSFET Q 1 , and a resistor R 2  coupled between the gate terminal and a source terminal of the MOSFET Q 1 . The resistors R 1 , R 2  form a voltage divider circuit. As such, when the power source  216  provides its input voltage to the protection circuit  202 , a sufficient voltage is applied to the gate terminal of the MOSFET Q 1  via the voltage divider circuit to bias the MOSFET Q 1  causing the MOSFET Q 1  to turn on. 
     In the particular example of  FIG.  2   , the resistor R 1  may have a large resistance value, and the resistor R 2  may have a smaller resistance value as compared to R 1 . For example, the resistor R 1  may have a value of about 100 kilo-ohms, and the resistor R 2  may have a value of about 15 kilo-ohms. In other examples, the resistors R 1 , R 2  may have other suitable resistance values such as more or less than 100 kilo-ohm, more or less than 15 kilo-ohms, etc. 
     As shown in  FIG.  2   , the control circuit  210  includes a controller  224  and an opto-coupler U 1 . The controller  224  may include various components for controlling the MOSFET Q 1  and the relay K 1  based on the sensed input voltage from the voltage sensor  212  and the sensed output voltage from the voltage sensor  214 .  FIG.  3    illustrates one example of the controller  224  of  FIG.  2   . 
     For example, and as shown in  FIG.  3   , the controller  224  includes a microcontroller (MCU)  326 , and drivers  328 ,  330 . The MCU  326  includes comparators  332 ,  334  and logic components  336 . During operation, the controller  224  receives the sensed input voltage from the voltage sensor  212  and the sensed output voltage from the voltage sensor  214 . In some examples, the MCU  326  and/or the sensors  212 ,  214  may include one or more analog-to-digital converters (not shown) to convert the sensed input voltage and/or the sensed output voltage into digital signals. The comparator  332  compares the sensed input voltage with a defined threshold Vth 1 , and the comparator  334  compares the sensed output voltage with a defined threshold Vth 2 . The logic components  336  receive the resulting comparisons from the comparators  332 ,  334 , and generate signals for the drivers  328 ,  330  to drive the MOSFET Q 1  (via the opto-coupler U 1 ) and the relay K 1 . The values of the defined thresholds Vth 1 , Vths of  FIG.  3    may be similar to the values of the defined thresholds of  FIG.  1   . 
     In other examples, the control circuit  210  may include other suitable components for controlling the MOSFET Q 1  and the relay K 1 . For example, the opto-coupler U 1  may be replaced with a magnetically coupled switching device such as a relay. 
     In the example of  FIGS.  2  and  3   , the control circuit  210  is powered by a supply voltage. This supply voltage may be provided by the input power source, and/or from an auxiliary supply. In such examples, the supply voltage may also provide power for driving the relay K 1  if desired. 
     The control circuit  210  may function in a similar manner as the control circuit  110  of  FIG.  1   . For example,  FIG.  4    illustrates a timing diagram  400  including waveforms of different parameters from the power supply  200  of  FIG.  2   . Specifically, the waveform  402  represents a rectified input voltage Vr provided to the protection circuit  202 , the waveform  404  represents an output voltage Vo of the protection circuit  202 , the waveform  406  represents a bulk voltage Vb between the PFC circuit  220  and the DC/DC power conversion circuit  222 , the waveform  408  represents the state of the relay K 1 , the waveform  410  represents the state of the MOSFET Q 1 , the waveform  412  represents a signal PFC for turning on/off the PFC circuit, and the waveform  414  represents a signal CONV for turning on/off the DC/DC power conversion circuit. 
     At startup, the input voltage Vr is at a rated peak voltage as shown by the waveform  402 , the MOSFET Q 1  is closed due to the input voltage providing a bias voltage to the MOSFET&#39;s gate terminal (as explained above), the relay K 1  is open, and the opto-coupler U 1  of the control circuit  210  is deactivated (e.g., turned off). As shown in  FIG.  4   , the signal PFC and the signal CONV are high indicating the PFC circuit and the DC/DC power conversion circuit are off. In such examples, current is passed through the protection circuit  202  via the MOSFET Q 1  causing the output voltage Vo to rise as a capacitor C (e.g., representing the effective capacitance in the power converter  218 ) charges. During this time, the MOSFET Q 1  may be operated in a PWM mode with a switching frequency between 100-120 Hz. In some examples, the MOSFET Q 1  may be operated in its active mode to charge the capacitor C. 
     After a time period t 1 , the sensed voltage (proportional to the output voltage Vo) reaches the defined threshold Vth 2 . In response, the control circuit  210  generates a control signal to turn on (e.g., close) the relay K 1  as shown by the waveform  408  transitioning to a high state. This provides a minimal series impedance path for the current passing through the protection circuit  202  to the power converter  218 . In some examples, the time period t 1  may be about 6 seconds. 
     After the relay K 1  is closed, the control circuit  210  activates the opto-coupler U 1  to turn off (e.g., open) the MOSFET Q 1  as shown by the waveform  410  transitioning to a low state. For example, when the opto-coupler U 1  is on, current is pulled from the gate terminal of the MOSFET Q 1  causing the MOSFET Q 1  to turn off. During this time, the resistors R 1 , R 2  set a minimum charging current when the MOSFET Q 1  is off. 
     As shown in  FIG.  4   , a delay (e.g., a time period t 2 ) may occur between closing the relay K 1  and opening the MOSFET Q 1 . In some examples, the delay may be about 50 milliseconds. 
     After the MOSFET Q 1  is off, the control circuit  210  may control the relay K 1  in a PWM mode as shown by the waveform  408  repeatedly transitioning between a high state and a low state. This ensures the output voltage Vo remains at a constant level. As shown in  FIG.  4   , a delay (e.g., a time period t 3 ) may occur between opening the MOSFET Q 1  and entering the PWM mode. This delay may be about 450 milliseconds. 
     When the relay K 1  is operating in its PWM mode, the signal PFC transitions to a low state to turn on the PFC circuit. This may occur a time period t 4  (e.g., 500 milliseconds) after the relay K 1  is operating in its PWM mode. Once the PFC circuit is enabled, the PFC output voltage Vb is regulated at, for example, a level higher than the peak AC input. This is shown in the waveform  406  at the end of time period t 4 . 
     After the PFC circuit is enabled, the signal CONV transitions to a low state to turn on the DC/DC power conversion circuit. In some examples, a delay (e.g., a time period t 5 ) may occur between enabling the PFC circuit and enabling the DC/DC power conversion circuit. This ensures an output of the PFC circuit is sufficient for the DC/DC power conversion circuit. In some examples, the delay may be about 2 seconds. At this point, the power converter  218  may be in a steady state to provide an output voltage (e.g., a regulated output voltage) to the load. 
     At some point, the input voltage Vr may increase causing an overvoltage condition OV PLD as shown in  FIG.  4    during a time period t 8 . This may cause the output voltage Vo and the PFC output voltage Vb to spike as shown in the waveforms  404 ,  406 , and the signal PFC to transition to a high state to disable the PFC circuit. Later, the signal CONV transitions to a high state (e.g., after the PFC circuit&#39;s output decays) to disable the DC/DC power conversion circuit. This initiates an overvoltage recovery condition, as represented by a time period t 9 . 
     At the beginning of the time period t 8 , the control circuit  210  determines that the sensed input voltage has exceeded the defined threshold Vth 1 . In response, the control circuit  210  turns off (e.g., opens) the relay K 1  as shown by the waveform  408  transitioning to a low state. At this time, the resistors R 1 , R 2  provide the only current path between the power source  216  and the power converter  218 . However, because the resistor R 1  has a high resistance as explained above, a negligible amount of current passes through this path. As such, the power converter  218  is effectively disconnected from the power source  216  after the relay K 1  is turned off. After the power converter  218  is disconnected, the capacitor C discharges causing the output voltage Vo (waveform  404 ) and the PFC output voltage Vb (waveform  406 ) to decrease. 
     Once the input voltage decreases Vr, the power supply  200  may enter a turn on delay period TON DELAY as shown in  FIG.  4   . During this time, the power converter  218  is reconnected to the power source  216  via the MOSFET Q 1 . For example, in response to the input voltage falling below the defined threshold Vth 1 , the control circuit  210  may turn off the opto-coupler U 1 . As a result, the MOSFET Q 1  is turned back on due to a bias voltage from the input voltage to charge (or recharge) the capacitor C, as explained above. After which, the previously explained steps may be repeated to bring the power converter  218  back to its steady state as explained above. 
     In some examples, the protection circuits disclosed herein may include current limiting functionality. In such examples, the protection circuits may include a circuit for limiting inrush current from the input power source. For example,  FIG.  5    illustrates a power supply  500  substantially similar to the power supply  200 , but including an inrush current limiting circuit  540 . The power supply  500  of  FIG.  5    includes a protection circuit  502  having the inrush current limiting circuit  540  coupled to the MOSFET Q 1 . Specifically, and as shown in  FIG.  5   , the inrush current limiting circuit  540  is coupled between the MOSFET Q 1  and the power converter  218 . As such, when the input voltage is present, the current limiting circuit  540  may limit input current to ensure a controlled amount of current passes through the MOSEFT Q 1  to the power converter  218 . 
     As shown in  FIG.  5   , the inrush current limiting circuit  540  includes a resistor R 3  and a transistor Q 2 . The resistor R 3  is coupled between the MOSFET Q 1  and the transistor Q 2 . Specifically, one end of the resistor R 3  is coupled to the source terminal of the MOSFET Q 1  and a base terminal of the transistor Q 2  (via a resistor R 4 ), and the other end of the resistor R 3  is coupled to an emitter terminal of the transistor Q 2 . A collector terminal of the transistor Q 2  is coupled to the gate terminal of the MOSFET Q 1 . 
     When operated, the limiting circuit  540  controls the amount of the current passing through the protection circuit  502 . For example, if the input current increases, a voltage drop across the resistor R 3  increases. Once the voltage drop across the resistor R 3  reaches the base-emitter voltage Vbe of the transistor Q 2 , the transistor Q 2  turns on (and operates in its active mode). As a result, some of the current applied to the gate terminal of the MOSEFT Q 1  is passed through the transistor Q 2 . This causes a reduction in the gate-source voltage Vgs of the MOSEFT Q 1  thereby reducing the conductivity of the MOSEFT Q 1  and limiting the current passing through the MOSEFT Q 1 . As such, the input current flowing through the MOSEFT Q 1  (and provided to the power converter  218 ) may be limited to a fixed value determined by the resistor R 3  and the transistor Q 2 . 
     The resistor R 3  may be any suitable value for creating a voltage drop to limit current through the MOSEFT Q 1 . In some examples, the value of the resistor R 3  may be low such as less than about 5 ohms. In other examples, the value may be higher if desired. 
     As shown in  FIG.  5   , the protection circuit  502  further includes the resistor R 4  coupled to the transistor Q 2 . Specifically, one end of the resistor R 4  is coupled to the base terminal of the transistor Q 2 , and the other end of the resistor R 4  is coupled to the resistor R 3  and the source terminal of the MOSFET Q 1 . During operation, the resistor R 4  limits the base voltage on the transistor Q 2  so it does not exceed a set base-emitter voltage Vbe rating. 
     In other examples, the protection circuits may have another suitable inrush current limiting circuit. For example,  FIG.  6    illustrates a power supply  600  substantially similar to the power supply  500 , but including a different inrush current limiting circuit. In the example of  FIG.  6   , the power supply  600  includes a protection circuit  602  having an inrush current limiting circuit  640  coupled on the MOSFET Q 1 . Specifically, the inrush current limiting circuit  640  includes a resistor R 5  coupled between the MOSFET Q 1  and the power converter  218  for limiting input current to ensure a controlled amount of current passes through the MOSEFT Q 1 . 
     In the particular example of  FIG.  6   , the MOSFET Q 1  may be operated in a switch mode. As such, if the input current increases, a voltage drop across the resistor R 5  increases. This voltage drop may decrease the gate-source voltage Vgs of the MOSEFT Q 1  thereby limiting the current passing through the MOSEFT Q 1 , as explained above. 
       FIG.  7    illustrates a power supply  700  substantially similar to the power supply  600 , but where the MOSFET Q 1  is controlled to turn on based on an auxiliary supply. Specifically, and as shown in  FIG.  7   , the power supply  700  includes a protection circuit  702  having an auxiliary supply AS coupled to the gate terminal of the MOSFET Q 1  for providing a bias voltage to the MOSFET Q 1 . More particularly, the auxiliary supply AS is coupled between the resistor R 1  and the opto-coupler U 1 . 
     During operation, the MOSFET Q 1  may turn on based on a bias voltage applied by the auxiliary supply AS. For example, once an input voltage is sensed, the control circuit  210  may activate the opto-coupler U 1 . As a result, the auxiliary supply AS provides the bias voltage to the gate terminal of the MOSFET Q 1  via the voltage divider (formed by the resistors R 1 , R 2 ) as explained above. 
     As shown in the examples of  FIGS.  1 ,  2  and  5 - 7   , the protection circuits  100 ,  202 ,  502 ,  602 ,  702  are coupled in a high-side rail (e.g., a positive rail, a supply rail, etc.) between the power sources and the power converters. In other examples, any one of the protection circuits disclosed herein may be coupled in a low-side rail (e.g., a reference rail, a return rail, etc.). For example,  FIG.  8    illustrates a power supply  800  substantially similar to the power supply  700 , but having a protection circuit  802  coupled in a low-side rail between the power source  216  and the power converter  218 . 
     In some examples, the protection circuits disclosed herein may include additional optional circuitry. For example, and as shown in  FIGS.  5 - 8   , the protection circuits  502 ,  602 ,  702 ,  802  each include a voltage regulating circuit to protect the MOSFET Q 1 . Specifically, and as shown in  FIGS.  5 - 8   , the protection circuits  502 ,  602 ,  702 ,  802  each include a diode (e.g., a zener diode) D 5  and a capacitor C 2  coupled in parallel with the diode D 5 . The diode D 5  and the capacitor C 2  are coupled between the gate and source terminals of the MOSFET Q 1 . In operation, the combination of the diode D 5  and the capacitor C 2  limits (e.g., clamps) the gate-source voltage Vgs of the MOSEFT Q 1 . 
     Additionally, the power supplies disclosed herein may include additional optional circuitry. For example, and as shown in  FIGS.  2  and  5 - 8   , the power supplies  200 ,  500 ,  600 ,  700 ,  800  each include an electromagnetic interference (EMI) filter and a rectifying circuit coupled between the AC power source  216  and the protection circuit  202 ,  502 ,  602 ,  702 ,  802 . In the particular examples of  FIGS.  2  and  5 - 8   , the rectifying circuit is shown as a diode bridge. In other examples, another suitable rectifying circuit may be employed if desired. Additionally, although the power supplies  200 ,  500 ,  600 ,  700 ,  800  include the EMI filter and the rectifying circuit, it should be apparent to those skilled in the art that either component may be removed, moved to another suitable location such as on the output side of the protection circuits, etc. 
     The sensors disclosed herein may be any suitable sensing device. For example, the sensors may be a resistive voltage sensor formed with a voltage divider as shown in  FIGS.  2  and  5 - 8   . In other examples, another suitable voltage sensing device may be employed. Additionally and/or alternatively, the sensors may sense a parameter other than an input and/or output voltage. In such examples, the parameter may be used to determine (e.g., calculate, estimate, etc.) the input and/or output voltage. 
     Additionally, and as shown in  FIGS.  2  and  5 - 8   , the input voltage sensors are coupled to sense an AC input voltage. In other examples, the input voltage sensors of  FIGS.  2  and  5 - 8    may be coupled in another suitable location to sense the input voltage. For example, the input voltage sensors may be coupled on the output side of the rectifying circuit to sense a rectified AC input voltage if desired. 
     The switching devices disclosed herein may include any suitable active switching device. For example, in the particular examples of  FIGS.  2  and  5 - 8   , the protection circuits include the MOSFET Q 1  coupled in a current path between their inputs and outputs, and the relay K 1  coupled across the MOSFET Q 1 . In such examples, the MOSFET Q 1  may be an N channel FET, and the relay K 1  may be a normally open relay. In other examples, the MOSFET Q 1  may be replaced with another suitable transistor such as an insulated-gate bipolar transistor (IGBT), and/or the relay K 1  may be replaced with another suitable switching device if desired. In some examples, the switching devices may be selected based on safe operating area (SOA) performances to ensure the switching devices may be safely operated. 
     The power sources disclosed herein may include any suitable power source. For example, the power sources may include an AC power source as shown in  FIGS.  2  and  5 - 8   . In such examples, the AC power source may include a power grid, a generator, etc. In other examples, the power sources may include a DC power source such as one or more batteries (e.g., rechargeable batteries), etc. 
     The power converters disclosed herein may include any suitable power converting circuitry. For example, the power converters may include an AC/DC power converter such as an AC/DC PFC circuit and a DC/DC power conversion circuit as shown in  FIGS.  2  and  5 - 8   . In other examples, the power converters may include a DC/DC power converter. For example,  FIG.  9    illustrates a power supply  900  substantially similar to the power supply  200 , but having a protection circuit  902  coupled between a DC power source  916  and a DC/DC power converter  918 . In such examples, the protection circuit  902  includes a diode D coupled between the MOSFTET Q 1  and the DC power source  916  to provide reverse current protection. As shown, the DC/DC power converter  918  may include a boost converter and a DC/DC power conversion circuit. 
     The protection circuit  902  of  FIG.  9    may include any one or more of the optional features explained herein. For example, although not shown, the protection circuit  902  may include circuitry for limiting inrush current such as the example circuitry shown in  FIGS.  5  and  6   . Additionally, the MOSFTET Q 1  may be self-biased in response to an input voltage from the power source  916  (as shown in  FIG.  9   ), and/or controlled to turn on based on an auxiliary supply as shown in  FIG.  7   . Further, the protection circuit  902  may be coupled in a high-side rail (as shown in  FIG.  9   ), or a low-side rail as explained herein. 
     Additionally, the power converters may include any suitable power conversion topology having one or more power switching devices. For example, the power converters may include one or more of a buck topology, a boost topology, a buck-boost topology, a forward topology, a flyback topology, a half-bridge topology, a full-bridge topology, and/or their resonant counterparts. 
     The control circuits disclosed herein may include an analog control circuit, a digital control circuit, or a hybrid control circuit (e.g., a digital control unit and an analog circuit). The digital control circuits may be implemented with one or more types of digital control circuitry. For example, the digital control circuits each may include a digital signal controller (DSC), a digital signal processor (DSP), a MCU, a field-programmable gate array (FPGA), an application-specific IC (ASIC), etc. In some examples, the control circuits may be used for controlling the switching devices of the protection circuits and at least portions of the power converters coupled to the protection circuits. For example, in the particular example of  FIG.  4   , the control circuit  210  includes the MCU  326  for controlling the MOSFET Q 1  and the relay K 1 . In some examples, the MCU  326  may also control portions of the PFC circuit if desired. 
     If, for example, the control circuit is a digital control circuit, the control circuit may be implemented with one or more hardware components and/or software. For example, instructions for performing any one or more of the features disclosed herein may be stored in and/or transferred from a non-transitory computer readable medium, etc. to one or more existing digital control circuits, new digital control circuits, etc. In such examples, one or more of the instructions may be stored in volatile memory, nonvolatile memory, ROM, RAM, one or more hard disks, magnetic disk drives, optical disk drives, removable memory, non-removable memory, magnetic tape cassettes, flash memory cards, CD-ROM, DVDs, cloud storage, etc. 
     The power supplies disclosed herein may be employed in any various applications. For example, the power supplies may be useful in outdoor power supply applications requiring excessive overvoltage protection such as at least 150% of the rated input voltage, high efficiency power supply applications, power supply applications including high-density conduction cooled systems, etc. In some examples, the power supplies may receive an AC input voltage ranging between 85 VAC and 275 VAC. 
     The protection circuits disclosed herein provide a compact and efficient approach with precise timing control to protect components (e.g., MOSFETs, diodes, capacitors, etc.) in the power converters. For example, and as explained herein, the protection circuits may provide protection during input overvoltage conditions by disconnecting the power converters from the input power sources, during excess input current conditions by precisely controlling inrush input current to limit the amount of current passed to the power converters, etc. Additionally, the protection circuits may provide the overvoltage and/or inrush current protection with significantly reduced losses and increased efficiency as compared to conventional approaches. Further, the protection circuits may be implemented with relative ease, require less board space, and require less complicated thermal management solutions in high density power supply applications as compared to conventional approaches including multiple relays. 
     The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure.