Bulk Capacitor Heating Circuit in Power Converter

Abstract

The power converter includes a power supply circuit having a bulk capacitor, an auxiliary circuit coupled to the power supply circuit for heating the bulk capacitor, and a control circuit coupled to the auxiliary circuit. The auxiliary circuit includes a switching device. The control circuit is configured to generate a control signal to control the switching device to allow the bulk capacitor to discharge and charge, thereby increasing a temperature associated with the bulk capacitor and reducing a value of equivalent series resistance associated with the bulk capacitor. Other exemplary auxiliary circuits and power converters are also disclosed.

Description

[Technical field]

[0001] The present disclosure relates to a bulk capacitor heating circuit in a power converter. [Background technology]

[0002] This section provides background information related to the present disclosure that is not necessarily prior art.

[0003] A power converter converts an input voltage and current into an output voltage and current. Power converters typically include one or more bulk capacitors located near the input and / or output of the converter. Bulk capacitors are typically used to prevent large voltage deviations due to, for example, load transients, input power transients, etc. Summary of the Invention

[0004] This section provides a summary of the disclosure, but is not an exhaustive disclosure of its entire scope or all of its features.

[0005] According to one aspect of the disclosure, a power converter includes a power supply circuit having a bulk capacitor, an auxiliary circuit coupled to the power supply circuit for heating the bulk capacitor, and a control circuit coupled to the auxiliary circuit, the auxiliary circuit including a switching device, the control circuit configured to generate a control signal to control the switching device to enable the bulk capacitor to discharge and charge to increase a temperature associated with the bulk capacitor and reduce a value of an equivalent series resistance associated with the bulk capacitor.

[0006] Further aspects and applicability areas will become apparent from the description provided herein. It should be understood that the various aspects of the present disclosure can 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 for illustrative purposes only and are not intended to limit the scope of the present disclosure.

[0007] The drawings described herein are for the purpose of illustrating only selected embodiments, not all possible implementations, and are not intended to limit the scope of the present disclosure. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a block diagram of a power converter including a power supply circuit having a bulk capacitor and an auxiliary circuit coupled to the power supply circuit for heating the bulk capacitor, according to an exemplary embodiment of the present disclosure. [Diagram 2] FIG. 2 is an electrical schematic diagram of an equivalent circuit of the bulk capacitor of FIG. 1. [Diagram 3] FIG. 2 is an electrical schematic diagram of a power converter including a power supply circuit having a bulk capacitor and an auxiliary circuit having a transformer, a diode, and a controllable switching device to charge and discharge the bulk capacitor according to another illustrative embodiment. [Figure 4] 4 is a graph of the current associated with the bulk capacitor of FIG. 3 in accordance with yet another illustrative embodiment. [Diagram 5] 4 is a graph of current through the switching device of FIG. 3 in accordance with another exemplary embodiment. [Figure 6] 4 is a graph of current through the diode of FIG. 3 in accordance with yet another illustrative embodiment. [Figure 7] FIG. 1 is an electrical schematic diagram of a power converter including a coupled inductor, a diode, and an auxiliary circuit having a switching device controllable to charge and discharge a bulk capacitor according to another illustrative embodiment. [Figure 8] FIG. 13 is an electrical schematic diagram of an auxiliary circuit further including a snubber circuit for heating a bulk capacitor of a power supply circuit according to yet another exemplary embodiment. [Figure 9] FIG. 4 is an electrical schematic diagram of a power converter including a power supply circuit having an AC / DC boost Power Factor Correction (PFC) topology and the auxiliary circuit of FIG. 3 in accordance with another exemplary embodiment. [Figure 10]FIG. 4 is an electrical schematic diagram of a power converter including a power supply circuit having an AC / DC bridgeless boost PFC topology and the auxiliary circuit of FIG. 3 in accordance with yet another illustrative embodiment. [Figure 11] FIG. 4 is an electrical schematic diagram of a power converter including a power supply circuit having a totem pole bridgeless boost PFC topology and the auxiliary circuit of FIG. 3 in accordance with another exemplary embodiment. [Figure 12] FIG. 4 is an electrical schematic diagram of a control circuit for generating a Pulse Width Modulated (PWM) control signal according to yet another illustrative embodiment. [Figure 13] FIG. 1 is an electrical schematic diagram of a control circuit for generating a Variable-Frequency Modulation (VFM) control signal in accordance with another exemplary embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Corresponding reference numerals indicate corresponding (but not necessarily identical) parts and / or features throughout the several views of the drawings.

[0010] The exemplary embodiments are provided so that the disclosure is thorough and fully conveys the scope to those skilled in the art. Numerous specific details are described, such as examples of specific components, devices, and methods, to provide a thorough understanding of the embodiments of the present disclosure. It will be apparent to those skilled in the art that specific details need not be used, that the exemplary embodiments can be embodied in many different forms, and that none of them should be construed to limit the scope of the present disclosure. In some exemplary embodiments, well-known processes, well-known device structures, and well-known technologies are not described in detail.

[0011] The terms used herein are for the purpose of describing specific exemplary embodiments only and are not intended to be limiting. As used herein, the singular forms "a," "an," and "the" may be intended to include the plural unless the context clearly indicates otherwise. The terms "comprises," "comprising," "including," and "having" are inclusive and thus specify the presence of stated features, integers, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof. The steps, procedures, and operations of the methods described herein should not necessarily be construed as necessarily requiring their execution in the particular order described or illustrated, unless specifically identified as an order of execution. It should also be understood that additional or alternative steps may be used.

[0012] Terms such as first, second, third, etc. may be used herein to describe various elements, components, regions, layers, and / or portions, but these elements, components, regions, layers, and / or portions should not be limited by these terms. These terms may be used only to distinguish one element, component, region, layer, or portion from another region, layer, or portion. Terms such as "first", "second", and other numerical terms, when used herein, do not imply sequence unless clearly indicated by the context. Thus, a first element, component, region, layer, or portion described below can be referred to as a second element, component, region, layer, or portion without departing from the teachings of the exemplary embodiments.

[0013] 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 the relationship of one element or feature depicted in a figure to another element or feature. Spatially relative terms may be intended to include different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if a device in a figure is turned over, an element described as "below" or "beneath" another element or feature would be placed "above" that other element or feature. Thus, the example term "below" can include 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.

[0014] Example embodiments will now be described more fully with reference to the accompanying drawings.

[0015] A power converter according to one exemplary embodiment of the present disclosure is shown in FIG. 1 and generally designated by reference numeral 100. As shown in FIG. 1, the power converter 100 includes a power supply circuit 102, an auxiliary circuit 104, and a control circuit 106. The power supply circuit 102 includes a bulk capacitor 108. The auxiliary circuit 104 is coupled to the power supply circuit 102 for heating the bulk capacitor 108. As shown, the auxiliary circuit 104 includes a switching device 110. The control circuit 106 is coupled to the auxiliary circuit 104. The control circuit 106 is configured to generate a control signal 112 to control the switching device 110 to allow the bulk capacitor 108 to discharge and charge to increase a temperature associated with the capacitor 108 and reduce a value of an equivalent series resistance (ESR) associated with the bulk capacitor 108.

[0016] Electrolytic capacitors such as bulk capacitor 108 typically include several elements. For example, Figure 2 shows an equivalent circuit of bulk capacitor 108 of Figure 1. As shown, bulk capacitor 108 includes a capacitance C, a resistance R in parallel with capacitance C, an ESR 220, and an equivalent series inductance (ESL) 222. Resistance R represents the insulation resistance of the bulk capacitor's dielectric. ESR 220 and ESL 222 are in series with capacitance C and resistance R, respectively, and represent the combination of resistive and inductive elements within bulk capacitor 108.

[0017] In some examples, bulk capacitor 108 and / or any one of the other bulk capacitors disclosed herein can have a large capacitance (e.g., capacitance C in FIG. 2). The capacitance of capacitor 108 can help reduce voltage deviations in power converter 100. For example, voltage deviations generally decrease as capacitance increases. Thus, bulk capacitor 108 and / or any one of the other bulk capacitors disclosed herein can have a capacitance in the range of, for example, 100 μF to over 1 mF.

[0018] The ESR associated with the bulk capacitor 108 (e.g., ESR 220 in FIG. 2) may be temperature dependent. For example, as the ambient temperature of the bulk capacitor 108 decreases (or increases), its ESR value may increase (or decrease). For example, in a cold environment (e.g., below −25 degrees Celsius, between −25 degrees Celsius and 20 degrees Celsius, above 20 degrees Celsius, etc.), when the power converter 100 is started up and the ambient temperature of the bulk capacitor 108 increases, the ESR of the capacitor may change significantly over time. In such an example, as the ambient temperature of the bulk capacitor 108 increases, the ESR of the capacitor may change by a factor of 10. In some examples, the impedance ratio of the bulk capacitor 108 at −40 degrees Celsius may be more than 10 times higher than the impedance ratio at 20 degrees Celsius.

[0019] When the power converter 100 starts up in a cold environment, the increased ESR can adversely affect the operation of the power converter 100. For example, when the power converter 100 starts up in a cold environment, the converter 100 can experience a large ripple voltage across the bulk capacitor 108 due (at least in part) to the increased ESR. This can occur, for example, when the bulk capacitor 108 is coupled to the output of the power converter 100 (e.g., as an output bulk capacitor). In some cases, this large ripple voltage can cause reduced output voltage regulation accuracy, activation of overvoltage protection circuits, control loop instability, etc. In another example, when the bulk capacitor 108 is coupled to the input of the power converter 10 (e.g., as an input bulk capacitor), the increased ESR can cause high frequency noise across the bulk capacitor 108 that can reduce its filtering effect.

[0020] However, by forcing the capacitor 108 to charge and discharge, the ESR value of the bulk capacitor 108 can be reduced. For example, charging / discharging the capacitor 108 can activate the electrolyte in the bulk capacitor 108 and increase the temperature associated with the capacitor 108 over time. This temperature change can be based, for example, on the frequency of charging and discharging. As a result of the increased temperature, the ESR value of the capacitor 108 can be reduced to an appropriate level. The reduced ESR value can minimize ripple voltage, noise, etc. across the capacitor 108.

[0021] In the example of FIG. 1, the switching device 110 of the auxiliary circuit may be coupled to the bulk capacitor 108 to forcefully charge and discharge the bulk capacitor. In such an example, the bulk capacitor 108 may be charged and discharged based on the state of the switching device 110. In this manner, as the switching device 110 turns on and off (by the generated control signal 112), the bulk capacitor 108 may be charged and discharged (e.g., as a voltage source). For example, the bulk capacitor 108 may charge when the switching device 110 is off (e.g., in its open state) and discharge its stored energy when the switching device 110 is on (e.g., in its closed state). Thus, the bulk capacitor 108 may receive a charging current when the switching device 110 is off, and the bulk capacitor 108 may provide a discharging current when the switching device 110 is on. In such an example, the capacitor 108 may be charged and discharged once per switching period of the switching device 110.

[0022] In some examples, the auxiliary circuit 104 may be activated based on a parameter of the power converter 100 to initiate a charge / discharge process to heat (e.g., pre-heat) the capacitor 108. For example, when the power converter 100 is powered up in a cold environment, the control circuit 106 may generate a control signal 112 for controlling the switching device 110 in response to the power converter 100 receiving input power. For example, the control circuit 106 may sense a parameter of the power converter 100 (e.g., input current, input voltage, etc.) and initiate generation of the control signal 112 in response to the sensed parameter. In such an example, the bulk capacitor 108 may be initially charged with the input power.

[0023] The control circuit 106 may stop generating the control signal 112 for controlling the switching device 110 in response to a parameter of the bulk capacitor 108 exceeding a defined threshold. In such an example, the switching device 110 may be turned off and the auxiliary circuit 104 may be deactivated to stop the charge / discharge process for heating the capacitor 108. For example, the relationship between the ESR and the temperature associated with the capacitor 108 may be known. In such an example, the control circuit 106 may sense the temperature associated with the capacitor 108 and stop generating the control signal 112 when the temperature rises above a defined value (e.g., 10 degrees Celsius, 20 degrees Celsius, 30 degrees Celsius, etc.). In such an example, the defined temperature may be determined based on a desired ESR associated with the capacitor 108. In another example, the control circuit 106 may determine an ESR value of the capacitor (e.g., based on a sensed current) and stop generating the control signal 112 when the ESR value falls below (e.g., exceeds) a defined value (e.g., 0.1 ohms, 0.09 ohms, etc.). In yet another example, the control circuit 106 can stop generating the control signal 112 when the number of charges and / or discharges of the bulk capacitor 108 exceeds a defined threshold.

[0024] Bulk capacitor 108 may be heated (e.g., preheated) before power converter 100 enters a start-up period. Thus, when power converter 100 is powered up in a cold environment, capacitor 108 may be heated to reduce the capacitor's ESR to a desired value before power converter 100 enters a start-up period (e.g., a period during which the converter's effective capacitance is charged and the converter is able to provide a desired stable output voltage). In other examples, the heating process may be part of a start-up process (e.g., an initial part of the start-up process). Once capacitor 108 is heated to a desired temperature (e.g., its ESR is reduced to a desired value), power converter 100 may enter, continue its start-up process, etc.

[0025] The control signal 112 provided to the switching device 110 may have any suitable frequency. The frequency may be fixed or variable. For example, the control signal 112 may have a set frequency or a varying frequency. In an example where the control signal 112 has a varying frequency, the control circuit 106 may provide variable-frequency modulation (VFM) control. The frequency may have a suitable value (e.g., in the range of 10 kHz to 1 MHz) to ensure high-frequency charging / discharging of the bulk capacitor 108. As a result, the bulk capacitor 108 may be charged / discharged a desired number of times such that a temperature associated with the capacitor 108 reaches a desired value.

[0026] Further, the control signal 112 may have a fixed or variable duty cycle. For example, the on-time of the switching device 110 (e.g., the discharge time of the capacitor 108) and the off-time of the switching device 110 (e.g., the charge time of the capacitor 108) may be fixed. In such an example, the charging current provided to the capacitor 108 and the discharging current provided by the capacitor 108 based on the state of the switching device 110 may be substantially constant for each charge / discharge cycle. In other examples, the duty cycle may vary. In such an example, the control signal may be a Pulse Width Modulated (PWM) signal.

[0027] The on and off times of control signal 112 (and thus switching device 110) as well as the charge and discharge currents may be determined based on various parameters to ensure that capacitor 108 is sufficiently heated before the output voltage is established. For example, the parameters may include the charge capacity of capacitor 108, the power supply start-up time (e.g., the time from when the input voltage is received to when the output voltage is established), etc.

[0028] In some examples, the auxiliary circuit 104 of Figure 1 can include one or more components in addition to the switching device 110. For example, Figure 3 shows a power converter 300 including a power supply circuit 302 having a bulk capacitor C1 and an auxiliary circuit 304 having a switching device, an inductive device, and a diode (e.g., a rectifier diode) D7. In some examples, the inductive device (e.g., a transformer, a coupled inductor, etc.) may be a physically small device as long as it allows for isolation.

[0029] In the particular example of Figure 3, the switching device is shown as a MOSFET Q4 and the inductive device is shown as a transformer TX1. In other examples, other suitable switching devices and / or inductive devices may be used. The auxiliary circuit 304 may be used with the power supply circuit 102 of Figure 1 and / or another suitable power supply circuit having a bulk capacitor.

[0030] In the example of Fig. 3, the MOSFET Q4, the transformer TX1 and the diode D7 of the auxiliary circuit 304 are configured in a flyback converter topology. More specifically, the auxiliary circuit 304 has an open-loop flyback converter topology. Thus, in the example of Fig. 3, the MOSFET Q4 of the auxiliary circuit 304 is controlled without feedback.

[0031] As shown, a primary winding P1 of a transformer TX1 is coupled between a bulk capacitor C1 and a MOSFET Q4. Specifically, in the example of FIG. 3, the primary winding P1 is coupled to a drain terminal of a MOSFET Q4. A source terminal of the MOSFET Q4 is coupled to a reference voltage (e.g., ground). As shown, a diode D7 is coupled between a secondary winding S1 of the transformer TX1 and the bulk capacitor C1. Specifically, the secondary winding S1 is coupled to the anode of the diode D7, and the bulk capacitor C1 is connected to the cathode of the diode D7.

[0032] In the particular example of Figure 3, the bulk capacitor C1 and the components of the auxiliary circuit 304 are coupled to ensure that the capacitor C1 charges and discharges. For example, as shown in Figure 3, the bulk capacitor C1 is coupled to discharge as a voltage source to the primary winding P1 of the transformer when the MOSFET Q4 turns on. During this time, the current from the bulk capacitor C1 is discharged through the primary winding P1 and the MOSFET Q4 to the reference voltage. As a result, the primary winding current increases and the transformer TX1 stores energy.

[0033] Furthermore, as shown in Figure 3, the secondary winding S1 of the transformer TX1 is coupled to charge the bulk capacitor C1 when the MOSFET Q4 is turned off. For example, when the MOSFET Q4 is turned off, the energy stored in the primary winding P1 of the transformer is transferred to the secondary winding S1. During this time, the energy in the secondary winding S1 is discharged, and the current flowing from the secondary winding S1 through the diode D7 to the capacitor C1 charges the bulk capacitor C1.

[0034] The charging / discharging process of the bulk capacitor C1 is illustrated in Figures 4-6. For example, Figures 4-6 show graphs 400, 500, and 600 of the capacitor current I_C1, the current I_Q4 flowing through the MOSFET Q4, and the current I_D7 flowing through the diode D7, respectively. As shown, the graphs 400, 500, and 600 include successive periods T1, T2, and T3 corresponding to the charging and discharging cycles of the bulk capacitor C1. Specifically, the period T1 corresponds to a discharging cycle of the capacitor C1, the period T2 corresponds to the next charging cycle of the capacitor C1, and the period T3 corresponds to another discharging cycle of the capacitor C1.

[0035] For example, MOSFET Q4 is on during time period T1. During this time period, capacitor C1 releases its stored energy, causing a current I_C1 to flow from the capacitor as shown in Figure 4. The capacitor current flows through MOSFET Q4 (and primary winding P1 as described above) as shown by the increasing current I_Q4 during time period T1 in Figure 5. During time period T1, no current flows through diode D7 as shown in Figure 6.

[0036] The MOSFET Q4 is off during the period T2. Therefore, as shown in FIG. 5, no current flows through the MOSFET Q4. During the period T2, as described above, the energy stored in the transformer TX1 is released back to the capacitor C1, so the diode current I_D7 and the capacitor current I_C1 increase sharply and then decrease over time (see FIG. 6 and FIG. 7). Thus, during this period, the capacitor C1 is charged from the energy stored in the transformer TX1.

[0037] During time period T3, MOSFET Q4 turns on again and the bulk capacitor C1 is again discharged through the primary winding P1 and MOSFET Q4, as described above. This charging / discharging process of the bulk capacitor C1 may be repeated as necessary.

[0038] MOSFET Q4 may be controlled by any suitable control circuit. In the particular example of FIG. 3, power converter 300 includes a control circuit represented by signal source V4 for controlling MOSFET Q4. In such an example, signal source V4 may provide a control signal to a gate terminal of MOSFET Q4 via resistor R3. In some examples, the control signal provided by signal source V4 may have any suitable frequency and / or fixed or variable duty cycle, as discussed above.

[0039] In some examples, the auxiliary circuit 304 may be activated and / or deactivated to start and / or stop the charging / discharging process of the bulk capacitor C1 based on one or more parameters of the power converter 300. For example, the signal source V4 may be controlled to generate its control signal in response to the power converter 300 receiving input power, as described above. In such an example, the bulk capacitor 108 may be first charged with the input power and then discharged when the MOSFET Q4 turns on. Furthermore, in response to a parameter of the bulk capacitor 108 exceeding (e.g., increasing above and / or decreasing below) a defined threshold, the signal source V4 may be controlled to stop generating its control signal. The parameter related to the bulk capacitor 108 may be, for example, a temperature, an ESR value, a number of charging and / or discharging times, etc. When the signal source V4 stops generating its control signal, the MOSFET Q4 remains off (e.g., open) and the auxiliary circuit 304 is deactivated.

[0040] Further, the power converter 300 of FIG. 3 may include one or more components for converting an input voltage and current to an output voltage and current. For example, as shown in FIG. 3, the power supply circuit 302 includes an optional rectifier circuit 314 having four diodes D6, D8, D9, and D10. In the example of FIG. 3, the diodes D6, D8, D9, and D10 are configured in a full bridge configuration to convert AC power from the AC power source V3 to DC power. In other examples, another suitable rectifier circuit may be used. Although not shown in FIG. 3, the power supply circuit 302 may further include one or more power switching devices, inductors, capacitors, etc.

[0041] In some examples, the auxiliary circuit 304 of FIG. 3 may include another suitable inductive device as described above. For example, FIG. 7 shows a power converter 700 including the power circuit 302 of FIG. 3, a control circuit (e.g., signal source V4), and an auxiliary circuit 704 including the MOSFET Q4 and diode D7 of FIG. 3, and a coupled inductor CI. The auxiliary circuit 704 functions similarly to the auxiliary circuit 304 of FIG. 3 for heating the bulk capacitor C1 in the power circuit 302. For example, the bulk capacitor C1 may discharge into the coupled inductor winding W1 as a voltage source when the MOSFET Q4 is on, and charge with a current flowing from the coupled inductor winding W2 (and through the diode D7) when the MOSFET Q4 is off.

[0042] In another example, any one of the auxiliary circuits disclosed herein may include a snubber circuit to suppress voltage spikes. For example, FIG. 8 illustrates an auxiliary circuit 804 that may be used with any one of the power supply circuits disclosed herein and / or another suitable power supply circuit. The auxiliary circuit 804 of FIG. 8 is substantially similar to the auxiliary circuit 304 of FIG. 3, but includes a snubber circuit 840 coupled across the primary winding P1 of the transformer TX1. As shown, the snubber circuit 840 includes a capacitor C2, a resistor R2, and a diode D2. The capacitor C2 and the resistor R2 are coupled in parallel, and the diode D2 is coupled between the parallel combination of the capacitor C2 and the resistor R2 and the primary winding P1. In the example of FIG. 8, the capacitor C2 may absorb energy generated by a voltage spike caused, for example, by the MOSFET Q4 changing state.

[0043] Further, any one of the auxiliary circuits disclosed herein may be used in any suitable power converter (e.g., switching power converter) having at least one bulk capacitor. For example, the auxiliary circuit may be used with power supply circuits having various converter topologies, such as buck, boost, buck-boost, etc. topologies, to provide AC / DC, DC / AC, and / or DC / DC power conversion. In some examples, the boost topology of the power supply circuit may include a PFC circuit. For example, FIGS. 9-11 show power converters 900, 1000, 1100 including power supply circuits 902, 1002, 1102 having various boost PFC topologies, the auxiliary circuit 304 of FIG. 3, and the control circuit (e.g., signal source V4) of FIG. 3 for controlling MOSFET Q4 of the auxiliary circuit 304. Specifically, the power supply circuit 902 of FIG. 9 has an AC / DC boost power factor correction (PFC) topology, the power supply circuit 1002 of FIG. 10 has an AC / DC bridgeless boost PFC topology, and the power supply circuit 1102 of FIG. 11 has a totem pole bridgeless boost PFC topology. In the power supply circuit 1002 of FIG. 10, some or all of the diodes D6, D7, D8, and D9 may be replaced with MOSFETs (e.g., SiC MOSFETs) if desired. Furthermore, in the power supply circuit 1102 of FIG. 11, some or all of the MOSFETs Q1 and Q5 may be replaced with diodes if desired.

[0044] Additionally, the control circuits disclosed herein may include any suitable circuitry for generating control signals for controlling switching devices in the auxiliary circuits. For example, the control circuits may include analog control circuits, digital control circuits, or hybrid control circuits (e.g., digital control circuits and analog circuits). The digital control circuits may be implemented with one or more types of digital control circuits. For example, each digital control circuit may include a digital controller, such as, for example, a digital signal controller (DSC), digital signal processing (DSP), a microcontroller, a field programmable gate array (FPGA), an application-specific IC (ASIC), or the like.

[0045] In some examples, the control circuit can implement PWM control or VFM control as described above. For example, FIG. 12 illustrates a control circuit 1206 employing PWM control, and FIG. 13 illustrates a control circuit 1306 employing VFM control. In some examples, the control circuit 1206 can include a logic component U3 that provides a signal to drive the transistors Q10, Q11, as shown in FIG. 12. Similarly, the control circuit 1306 can include a voltage-controlled oscillator (VCO) 1350 that provides a clock signal CLK (e.g., having a 50% duty cycle) to drive the transistors Q8, Q9, as shown in FIG. 13.

[0046] Any one of the control circuits 1206, 1306 may be used to control the switching devices in any one of the auxiliary circuits disclosed herein. For example, transistors Q10, Q11 of FIG. 12 are controlled by logic component U3 to generate a PWM control signal for controlling MOSFET Q4 in auxiliary circuit 304 of FIG. 3. Additionally, transistors Q8, Q9 of FIG. 13 are controlled by VCO 1350 to generate a VFM control signal for controlling MOSFET Q4 in auxiliary circuit 304 of FIG. 3.

[0047] Additionally, the control circuits 1206, 1306 may disable operation of their associated auxiliary circuits. In such an example, the control circuits 1206, 1306 may receive, generate, etc., an enable signal to disable operation of the auxiliary circuits. For example, the logic component U3 of FIG. 12 and the VCO 1350 of FIG. 13 may be activated by an enable signal. If the enable signal is not provided, operation of the logic component U3 and the VCO 1350 may be disabled. As a result, no signal is provided to drive the transistors Q8, Q9, Q10, and Q11 of FIG. 12 and FIG. 13, and the transistors Q8, Q9, Q10, and Q11 do not generate a control signal to control the MOSFET Q4. In such an example, the MOSFET Q4 remains off, and operation of the auxiliary circuit 304 may be disabled to stop the charge / discharge process.

[0048] By using the auxiliary circuit disclosed herein, bulk capacitors in a power converter can be effectively heated in a short period of time, at least in part due to the heating, to reduce the ESR value associated with the bulk capacitor (e.g., an electrolytic capacitor). As a result, ripple voltage, noise, etc. in the power converter due to high ESR values ​​(e.g., in cold environments) can be minimized. In this manner, the auxiliary circuit can prevent overvoltage protection from being triggered, reduce output ripple over-specification, and improve control loop stability.

[0049] The foregoing description of the embodiments is provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the present disclosure. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment and, where applicable, are interchangeable and can be used in selected embodiments even if not specifically shown or described. The same may also be modified in many ways. Such variations should not be considered as departures from the present disclosure, and all such modifications are intended to be included within the scope of the present disclosure.

Claims

1. a power supply circuit including a bulk capacitor; an auxiliary circuit coupled to the power supply circuit for heating the bulk capacitor, the auxiliary circuit including a switching device; a control circuit coupled to the auxiliary circuit and configured to generate a control signal to control the switching device to allow the bulk capacitor to discharge and charge to increase a temperature associated with the bulk capacitor and to reduce a value of an equivalent series resistance associated with the bulk capacitor; Equipped with 1. A power converter comprising: a first winding coupled between a bulk capacitor of the power supply circuit and a switching device of the auxiliary circuit;

2. The power converter of claim 1 , wherein the bulk capacitor is coupled to discharge into the first winding when the switching device is turned on.

3. The power converter of claim 1 , wherein the auxiliary circuit includes a diode coupled between the second winding of the inductive device and the bulk capacitor of the power supply circuit.

4. The power converter of claim 3 , wherein when the switching device is turned off, the second winding is coupled to charge the bulk capacitor through the diode.

5. 2. The power converter of claim 1, wherein the inductive device comprises a transformer, the first winding being a primary winding of the transformer, and the second winding being a secondary winding of the transformer.

6. A power converter as claimed in claim 1 , wherein the inductive device comprises a coupled inductor.

7. A power converter as claimed in any preceding claim, wherein the control circuit is configured to generate the control signal having a fixed duty cycle.

8. A power converter as claimed in any preceding claim, wherein the auxiliary circuit comprises an open loop flyback converter topology.

9. A power converter as claimed in any preceding claim, wherein the control circuit is configured to generate the control signal for controlling the switching device in response to the power supply circuit receiving power.

10. 10. A power converter as claimed in claim 1, wherein in response to a parameter of the bulk capacitor exceeding a defined threshold, the control circuit is configured to cease generating the control signal.

11. A power converter as claimed in any preceding claim, wherein the control signal is a PWM control signal.

12. A power converter as claimed in any preceding claim, wherein the control signal has a variable frequency.

13. 13. A power converter as claimed in any preceding claim, wherein the power supply circuit comprises a bridge rectifier circuit.

14. 14. A power converter as claimed in any preceding claim, wherein the power supply circuit includes a power factor correction circuit.

15. A power converter according to any one of claims 1 to 14, wherein the control circuitry comprises analogue and / or digital circuitry.

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