TW202406292A - Power supply circuit with sufficient hold time in high-frequency varying load condition - Google Patents

Abstract

A power supply circuit includes a transformer, a power switch, an input voltage detecting circuit, a varying load detecting circuit, a steady-state current circuit, a first control circuit and a second control circuit. The first control circuit provides a first control signal for periodically turning on and off the power switch, thereby allowing the transformer to convert an input voltage into an output voltage. The input voltage detecting circuit monitors the status of the input voltage, and the varying load detecting circuit monitors the frequency and the peak of the output voltage. Based on the status of the input voltage, the frequency of the output voltage and the peak of the output voltage, the second control circuit determines whether a high-frequency varying load condition is satisfied, and activates the state-converting function of the steady-state current circuit for converting the output current associated with the output current from a varying state to a steady state.

Description

A power supply circuit that provides sufficient sustaining time under high-frequency dynamic load changing conditions

The present invention relates to a power supply circuit, and in particular, to a power supply circuit that can provide sufficient sustaining time under high-frequency dynamic load changing conditions.

Different components in computer systems require different operating voltages, so power supplies are commonly used to convert alternating current (AC) indoor power into direct current (DC) through transformation, rectification and filtering to drive different components. components. Prior art power supplies typically include a rectifier, a transformer, a power switch, a pulse width modulation integrated circuit, and energy storage components (such as input capacitors and magnetizing inductors). By using a specific frequency to switch the power switch, the power supply can repeatedly charge or discharge the energy storage element according to an input voltage from the mains supply, thereby providing an output voltage different from the input voltage. The pulse width modulation integrated circuit can control the switching condition according to a feedback voltage of the relevant output voltage, and then appropriately adjust the value of the output voltage to maintain a constant output.

When the mains power is removed, the power of the load-side device will be continuously supplied by the output capacitor of the power supply for a period of time. This period of time is the hold time defined in the specifications. To be more clear, the hold-up time refers to the length of time that the output voltage can maintain the output level normally after the power supply is turned off or powered off. Since the maintenance time is to ensure that the power output of the power system will not be unstable due to factors such as instant short circuit, overload, power outage or voltage drop, the most stringent conditions will be considered in the specifications. Generally, low voltage at the input end and Define the minimum value of the holding time under the condition that the output is fully loaded.

With the improvement of computer system configuration and software firmware, its working mode is often not a stable load condition, but may be a complex high-frequency dynamic load condition. At this time, the dynamic current value of the load is often greater than the maximum power supply. Output current value. Since the dynamic current of the load is in a high-frequency state, its instantaneous period is short, so the power supply can still operate normally. However, if the mains power is removed instantly under such high-frequency dynamic load changing conditions, the energy of the output capacitor will be quickly drained due to the excessive dynamic current value, making the power supply's maintenance time too short and unable to continuously supply power to the system. . Therefore, there is a need for a power supply circuit that can provide sufficient sustaining time under high-frequency dynamic load changing conditions.

The present invention provides a power supply circuit that can provide sufficient maintenance time under high-frequency dynamic load changing conditions, which includes a transformer, a power switch, an input voltage detection circuit, a dynamic load changing detection circuit, and a steady-state current circuit, a first control circuit and a second control circuit. The transformer is used to induce the energy of an input voltage from a primary side to a secondary side to supply an output voltage. It includes a primary side disposed on the primary side and including a first dotting terminal and a first non-dominating terminal. a winding, and a secondary side winding disposed on the secondary side and including a second dotted end and a second non-dotted end. A first terminal of the power switch is coupled to the first non-dominating terminal of the primary side winding, a second terminal is coupled to a first ground potential, and a control terminal is used to receive a first control signal. The input voltage detection circuit is coupled between the input voltage and the first ground potential and is used to provide a first detection voltage related to the input voltage. The dynamic load change detection circuit is coupled between the output voltage and the second terminal of the secondary side winding, and is used to provide a second detection voltage related to the value of the output voltage, and related to the output voltage A third detection voltage of the peak value. The steady-state current circuit is coupled between the second non-dominating end of the secondary side winding and the output voltage, and is used to selectively activate a transition function according to a second control signal to change the relevant output voltage. A state of output current. The first control circuit is disposed on the primary side and is used to provide a power supply status signal according to the first detection voltage and provide the first control signal. The second control circuit is disposed on the secondary side and is used to determine the state of the input voltage based on the power supply status signal, to obtain an instantaneous frequency of the output voltage based on the second detection voltage, and to determine the instantaneous frequency of the output voltage based on the second detection voltage. The instantaneous frequency and the third detection voltage are used to determine whether the output voltage meets a high-frequency dynamic load changing condition, and when it is determined that the output voltage meets the high-frequency dynamic load changing condition, the second control signal is output to activate the The transition function of the steady-state current circuit is to convert the output current from a dynamic load-changing state to a stable state.

Figure 1 is a schematic diagram of a power supply circuit 100 that can provide sufficient sustaining time under high-frequency dynamic load changing conditions according to an embodiment of the present invention. The power supply circuit 100 includes a power switch Q1, an input capacitor C _IN , an output capacitor C _OUT , a magnetizing inductor LM, an auxiliary diode DA, an auxiliary capacitor CA, an output diode D _OUT and a transformer TR , a rectifier 10, an input voltage detection circuit 20, a dynamic load change detection circuit 30, a steady-state current circuit 40, a first control circuit 50, and a second control circuit 60. The power supply circuit 100 can convert the AC voltage V _AC supplied by the commercial power into an output voltage V _OUT to drive a load (not shown). The input voltage detection circuit 20 can detect the state of the AC voltage V _AC to determine whether the AC voltage V _AC exists. The dynamic load change detection circuit 30 can detect the peak value of the output voltage V _OUT , and the second control circuit 60 can detect the current instantaneous frequency of the output voltage V _OUT , and determine the output voltage based on the peak value and the instantaneous frequency of the output voltage V _OUT . Whether V _OUT meets the high-frequency dynamic load changing conditions.

Figure 2 is a schematic diagram of the implementation of the power supply circuit 100 in the embodiment of the present invention. The rectifier 10 can be a bridge rectifier, which includes diodes D1-D4, and is used to convert the AC power supply V _AC supplied by the mains into the input voltage V _IN , where I _IN represents the input current of the power supply circuit 100, and I _OUT represents The output current of the power supply circuit 100. However, the implementation of the rectifier 10 does not limit the scope of the present invention.

The transformer TR includes a primary side winding (represented by the number of turns NP), a secondary side winding (represented by the number of turns NS), and an auxiliary winding (represented by the number of turns NA), in which the primary side winding NP and the auxiliary winding NA is set on the primary side of the transformer TR, and the secondary side winding NS is set on the secondary side of the transformer TR. The first end of the magnetizing inductor LM is coupled to the dot end of the primary side winding NP in the transformer TR, and the second end is coupled to the non-dot end of the primary side winding NP in the transformer TR. The first terminal of the input capacitor C _IN is coupled to the junction terminal of the primary side winding NP in the transformer TR, and the second terminal is coupled to a ground potential GND1. The anode of the output diode D _OUT is coupled to the non-junction end of the secondary winding NS in the transformer TR, and the cathode is coupled to the output end (output voltage V _OUT ) of the power supply circuit 100 through the steady-state current circuit 40 . The first end of the output capacitor C _OUT is coupled to the output end of the power supply circuit 100 through the steady-state current circuit 40, and the second end is coupled to the node end of the secondary winding NS in the transformer TR, where the secondary side of the transformer TR The node end of the side winding NS is coupled to a ground potential GND2. The anode of the auxiliary diode DA is coupled to the non-junction end of the auxiliary winding NA in the transformer TR, and the cathode is coupled to the first control circuit 50 . The first terminal of the auxiliary capacitor CA is coupled to the cathode of the auxiliary diode D _OUT , and the second terminal is coupled to the ground potential GND1.

The first terminal of the power switch Q1 is coupled to the non-dominating terminal of the primary side winding NP of the transformer TR, the second terminal is coupled to the ground potential GND1, and the control terminal is coupled to the first control circuit 50 to receive a control signal GD1. The power switch Q1 will perform high-frequency switching between the on and off states according to the control signal GD1, and then periodically induce the primary side energy of the transformer TR to the secondary side winding NS through the primary side winding NP.

In the present invention, the first control circuit 50 may be a pulse width modulation (PWM) integrated circuit, which includes pins P1 - P4 and is disposed on the primary side of the transformer 30 . The pin P1 is a detection pin coupled to the input voltage detection circuit 20 for receiving a detection voltage VS1. Pin P2 is a control pin coupled to the power switch Q1 and is used to output the control signal GD1 to the control terminal of the power switch Q1. The pin P3 is coupled to the second control circuit 60 for outputting a power supply status signal S1 to communicate with the second control circuit 60 . Pin P4 is a power pin coupled to the auxiliary winding NA of the transformer TR through the auxiliary diode DA and the auxiliary capacitor CA, and is used to receive a power signal VCC. However, the implementation of the first control circuit 50 does not limit the scope of the present invention.

In the present invention, the second control circuit 60 may be a pulse width modulation integrated circuit, which includes pins P5-P8 and is disposed on the secondary side of the transformer 30. The pin P5 is coupled to the pin P3 of the first control circuit 50 to receive the power supply status signal S1. The pin P6 is a detection pin coupled to the dynamic load change detection circuit 30 for receiving a detection voltage VS2 related to the value of the output voltage V _OUT . The pin P7 is a detection pin coupled to the dynamic load change detection circuit 30 for receiving a detection voltage VS3 corresponding to the peak value of the relevant output voltage V _OUT . Pin P8 is a control pin coupled to the steady-state current circuit 40 and is used to output a control signal GD2 to selectively activate the transition function of the steady-state current circuit 40 . However, the implementation of the second control circuit 60 does not limit the scope of the present invention.

In the present invention, the input voltage detection circuit 20 may include two voltage dividing resistors R1 and R2, which are connected in series between the node of the primary winding NP in the transformer TR and the ground potential GND1, where the pin P1 of the first control circuit 50 Coupled between voltage dividing resistors R1 and R2. The input voltage V _IN converted by the rectifier 10 from the _AC power supply V AC will be established on the input voltage detection circuit 20. After the voltage is divided by the voltage dividing resistors R1 and R2, the detection voltage VS1 can be established on the voltage dividing resistor R2. Therefore, the first control circuit 50 can determine the state of the input voltage V _IN based on the value of the detection voltage VS1 received by its pin P1, and then control the power supply status signal S1 output by the pin P3 accordingly. In one embodiment, when the mains power supplies the AC power V _AC normally, the corresponding input voltage V _IN and the detection voltage VS1 are both in a non-0V voltage state. At this time, the first control circuit 50 can output the third voltage at the pin P3. A power supply status signal S1 of a level (such as a high level); when the mains stops supplying the AC power supply V _AC , the corresponding input voltage V _IN and the detection voltage VS1 are both in a 0V voltage state. At this time, the first control circuit 50 The power supply status signal S1 with a second level (such as a low level) can be output at the pin P3.

In the present invention, the dynamic load change detection circuit 30 includes a detection resistor RS and a comparator CP. The first terminal of the detection resistor RS is coupled to the node of the secondary winding NS in the transformer TR, and the second terminal is coupled to the output terminal (output voltage V _OUT ) of the power supply circuit 100 . When the output current I _OUT of the relevant output voltage V _OUT flows through the detection resistor RS, the detection voltage VS2 will be established on the detection resistor RS. As mentioned above, the second control circuit 60 can be a pulse width modulation integrated circuit. When receiving the detection voltage VS2 through the pin P6, the built-in frequency detection function can be used to obtain the detection voltage VS2. Instantaneous frequency, and then find the instantaneous frequency corresponding to the output voltage V _OUT .

On the other hand, the first input terminal of the comparator CP is coupled to the second terminal of the detection resistor RS to receive the detection voltage VS2, the second input terminal is coupled to a reference voltage _VREF , and the output terminal is coupled to the first The pin P7 of the second control circuit 60 can output the corresponding detection voltage VS3 according to the magnitude relationship between the detection voltage VS2 and the reference voltage V _REF . In one embodiment, when the value of the detection voltage VS2 is greater than the value of the reference voltage V _REF , the comparator CP will output the detection voltage VS3 with a third level (such as a high level) at the output end; When the value of the voltage VS2 is not greater than the value of the reference voltage V _REF , the comparator CP will output a detection voltage VS3 with a fourth level (eg, a low level) at the output end.

In the present invention, the second control circuit 60 determines the state of the input voltage V _IN based on the power supply status signal S1 received by the pin P5. When the AC power supply V _AC is normally supplied by the mains, the corresponding input voltage V _IN and the detection voltage VS1 are both in a non-0V voltage state. At this time, the first control circuit 50 can output a first level (such as Micro Motion) at the pin P3. bit) to the pin P5 of the second control circuit 60. At this time, the second control circuit 60 can determine that the input voltage V _IN is in a normal power supply state. When the mains power stops supplying the AC power V _AC , the corresponding input voltage V _IN and the detection voltage VS1 are both in a 0V voltage state. At this time, the first control circuit 50 can output a second level (such as a low level) at the pin P3 ) to the pin P5 of the second control circuit 60. At this time, the second control circuit 60 can determine that the input voltage V _IN is in an abnormal power supply state.

In the present invention, the second control circuit 60 determines whether the output voltage V _OUT meets the high-frequency load changing condition based on the detection voltage VS2 received by the pin P6 and the detection voltage VS3 received by the pin P7. When the second control circuit 60 determines that the instantaneous frequency of the detection voltage VS2 is higher than a critical value and the detection voltage VS3 has a third level (for example, a high level), it means that the output voltage V _OUT has a high peak value and changes drastically. At this time, the second control circuit 60 will determine that the output voltage V _OUT meets the high-frequency load changing conditions. When the instantaneous frequency of the detection voltage VS2 is not higher than the critical value and/or the detection voltage VS3 has a fourth level (such as a low level), it means that the output voltage V _OUT may have a high peak value but does not change drastically or change drastically. However, it does not have a high peak value, or it does not have a high peak value and does not change drastically. At this time, the second control circuit 60 will determine that the output voltage V _OUT does not meet the high-frequency load change conditions.

In the present invention, the second control circuit 60 determines based on the power supply status signal S1 received by the pin P5, the detection voltage VS2 received by the pin P6, and the detection voltage VS3 received by the pin P7. The level of the control signal GD2 output at pin P8 selectively activates the transition function of the steady-state current circuit 40 .

During the AC mains power supply period, the input voltage V _IN will first charge the input capacitor C _IN and stimulate the exciting inductor LM to start storing energy. At the same time, the first control circuit 50 outputs a control signal GD1 that switches between the enable potential and the disable potential in a specific duty cycle, so that the power switch Q1 can perform high-frequency switching between the on and off states. . During the conduction period of the power switch Q1, the primary side energy of the transformer TR can be induced to the secondary side winding NS through the primary side winding NP, thereby charging the output capacitor C _OUT to provide the output voltage V _OUT . At the same time, the primary side energy of the transformer TR will also be induced to the auxiliary winding NA through the primary side winding NP, and charge the auxiliary capacitor CA through the forward biased auxiliary diode DA, thereby providing the power signal VCC to the first control circuit The pin P4 of 50 supplies power required for the operation of the first control circuit 50 . In this case, when it is determined that the input voltage V _IN is in the normal power supply state according to the power supply status signal S1, the second control circuit 60 will output the control signal GD2 with the fifth level (eg, low level) at the pin P8 to Turn off the transition function of the steady-state current circuit 40 .

When the mains power stops supplying the AC power V _AC , the corresponding input voltage V _IN and the detection voltage VS1 are both in a 0V voltage state. At this time, the first control circuit 50 can output a second level (such as a low level) at the pin P3 ) to the pin P5 of the second control circuit 60 . When the second control circuit 60 determines that the input voltage V _IN is in an abnormal power supply state based on the power supply status signal S1, if the second control circuit 60 determines that the output voltage V _OUT meets the high-frequency variable load based on the signals received from its pins P6 and P7 When conditions are met, a control signal GD2 with a sixth level (eg, a high level) is output at pin P8 to activate the transition function of the steady-state current circuit 40 .

In an embodiment of the present invention, the steady-state current circuit 40 includes a resistor RX, an inductor LX and a switch Q2. The first terminal of the resistor RX is coupled to the cathode of the output diode D _OUT , and the second terminal is coupled to the output terminal (output voltage V _OUT ) of the power supply circuit 100. The first terminal of the inductor LX is coupled to the cathode of the output diode D _OUT , and the second terminal is coupled to the switch Q2. The first terminal of the switch Q2 is coupled to the second terminal of the inductor LX, the second terminal is coupled to the output terminal of the power supply circuit 100 (output voltage V _OUT ), and the control terminal is coupled to the pin of the second control circuit 60 P8 receives the control signal GD2. The switch Q2 switches between the on and off states according to the control signal GD2, thereby selectively turning on and off the signal transmission between the second terminal of the inductor LX and the output terminal (output voltage V _OUT ) of the power supply circuit 100 path.

Figure 3 is a schematic diagram of relevant signals during operation of the power supply circuit of the prior art. FIG. 4 is a schematic diagram of relevant signals during operation of the power supply circuit 100 in the embodiment of the present invention. For the purpose of explanation, it is assumed that the output voltage V _OUT meets the high-frequency dynamic load change condition, the mains power supplies the AC power V _AC normally before the time point T1, and the mains power stops supplying the AC power V _AC after the time point T1.

As shown in Figure 3, when the output voltage V _OUT meets the high-frequency dynamic load changing conditions, when the mains power is instantly removed at time point T1, the power supply circuit of the prior art will change due to the value of the dynamic output current I _OUT . If it is too large, the energy of the output capacitor C _OUT will be drained out quickly, resulting in the maintenance time TH1 (T2-T1) being too short, causing the power supply to be unable to continuously supply power to the system.

As shown in Figure 4, when the output voltage V _OUT meets the high-frequency dynamic load changing conditions, when the mains power is instantly removed at time point T1, the power supply circuit 100 of the present invention will start the steady-state current circuit 40. state function, thereby converting the output current I _OUT from a dynamic load changing state to a stable state. In one embodiment, the current value I _STEADY of the output current I _OUT in the steady state is designed to be the maximum rated output current of the power supply circuit 100, which will not quickly exhaust the energy of the output capacitor C _OUT , making the present invention The power supply circuit 100 can still provide sufficient holding time TH2 (T3-T1) to prevent high-frequency dynamic load changes from shortening the holding time and causing rapid power outage.

In the embodiment of the present invention, the power switch Q1 and the switch Q2 can be a metal-oxide-semiconductor field-effect transistor (MOSFET) or a bipolar junction transistor (BJT). ), or other components with similar functions. However, the types of the power switch Q1 and the switch Q2 do not limit the scope of the present invention.

To sum up, the power supply circuit of the present invention uses the input voltage detection circuit to monitor the state of the input voltage, and uses the dynamic load variation detection circuit to monitor the instantaneous frequency and peak value of the output voltage V _OUT to determine whether it meets the high-frequency load variation requirement. Conditions, and when it is determined that the high-frequency load changing conditions are met, the transition function of the steady-state current circuit is activated to convert the output current from a dynamic load-changing state to a stable state. Therefore, the power supply circuit of the present invention can provide sufficient sustaining time under high-frequency dynamic load changing conditions. The above are only preferred embodiments of the present invention, and all equivalent changes and modifications made in accordance with the patentable scope of the present invention shall fall within the scope of the present invention.

10: Rectifier 20: Input voltage detection circuit 30: Dynamic load change detection circuit 40: Steady-state current circuit 50: First control circuit 60: Second control circuit 100: Power supply circuit TR: Transformer NP: Primary side winding and Number of turns NS: Secondary side winding and number of turns NA: Auxiliary winding and number of turns CP: Comparator Q1: Power switch Q2: Switch D _OUT : Output diode D1-D4: Diode DA: Auxiliary diode R1 , R2: Voltage dividing resistor RX: Resistor RS: Detection resistor LM: Excitation inductor LX: Inductor C _IN : Input capacitor C _OUT : Output capacitor CA: Auxiliary capacitor I _{IN: Input current I OUT :} Output current V _IN : Input voltage V _OUT : Output voltage V _AC : AC voltage V _REF : Reference voltage VCC: Power signal VS1, VS2, VS3: Detection voltage GD1, GD2: Control signal S1: Power supply status signal GND1, GND2: Ground potential T1-T3: Time Points P1-P8: Pin positions

Figure 1 is a schematic diagram of a power supply circuit that can provide sufficient sustaining time under high-frequency dynamic load changing conditions according to an embodiment of the present invention. Figure 2 is a schematic diagram of an implementation method of a power supply circuit that can provide sufficient sustaining time under high-frequency dynamic load changing conditions according to an embodiment of the present invention. Figure 3 is a schematic diagram of relevant signals during operation of the power supply circuit of the prior art. Figure 4 is a schematic diagram of relevant signals during operation of the power supply circuit in the embodiment of the present invention.

10: Rectifier

20:Input voltage detection circuit

30: Dynamic load change detection circuit

40:Steady-state current circuit

50: First control circuit

60: Second control circuit

100:Power supply circuit

TR: Transformer

NP: Primary side winding and number of turns

NS: Secondary side winding and number of turns

NA: Auxiliary winding and number of turns

Q1: Power switch

D _OUT : output diode

DA: auxiliary diode

LM: magnetizing inductor

C _IN :Input capacitance

C _OUT : output capacitor

CA: auxiliary capacitor

I _IN :Input current

I _OUT : output current

V _IN :Input voltage

V _OUT :Output voltage

V _AC : AC voltage

GND1, GND2: ground potential

Claims (10)

A power supply circuit that can provide sufficient maintenance time under high-frequency dynamic load changing conditions, which includes: A transformer used to induce the energy of an input voltage from a primary side to the secondary side to supply an output voltage, which includes: A primary side winding is provided on the primary side and includes a first dotted end and a first non-dotted end; and The primary side winding is provided on the secondary side and includes a second dotted end and a second non-dotted end; A power switch containing: a first end coupled to the first non-dominating end of the primary side winding; a second terminal coupled to a first ground potential; and a control terminal for receiving a first control signal; an input voltage detection circuit coupled between the input voltage and the first ground potential for providing a first detection voltage related to the input voltage; A dynamic load change detection circuit is coupled between the output voltage and the second terminal of the secondary side winding for providing a second detection voltage related to the value of the output voltage, and related to the output a third detection voltage of the peak value of the voltage; A steady-state current circuit, coupled between the second non-dominating end of the secondary side winding and the output voltage, is used to selectively activate a transition function according to a second control signal to change the relevant output The state of voltage and output current; A first control circuit, disposed on the primary side, is used to provide a power supply status signal according to the first detection voltage, and to provide the first control signal; and A second control circuit, provided on the secondary side, is used to: Determine the status of the input voltage based on the power supply status signal; Find an instantaneous frequency of the output voltage based on the second detection voltage; Determine whether the output voltage meets a high-frequency dynamic load change condition based on the instantaneous frequency of the output voltage and the third detection voltage; and When it is determined that the output voltage meets the high-frequency dynamic load changing condition, the second control signal is output to activate the transition function of the steady-state current circuit to convert the output current from a dynamic load changing state to a stable state. The power supply circuit as claimed in claim 1, wherein the input voltage detection circuit includes: A first voltage dividing resistor, which includes: a first terminal coupled to the first terminal of the primary side winding of the transformer to receive the input voltage; and a second terminal coupled to the first control circuit; and A second voltage dividing resistor, which includes: a first terminal coupled to the second terminal of the first voltage dividing resistor; and a second terminal coupled to the first ground potential. The power supply circuit as described in claim 1, wherein the steady-state current circuit includes: A resistor containing: a first end coupled to the second non-pointing end of the secondary side winding in the transformer; and a second terminal coupled to the output voltage; and An inductor containing: a first end coupled to the second non-pointing end of the secondary side winding in the transformer; and a second end; and A switch containing: a first terminal coupled to the second terminal of the inductor; a second terminal coupled to the output voltage; and A control terminal is coupled to the second control circuit to receive the second control signal. The power supply circuit as described in claim 1, wherein the dynamic load change detection circuit includes: A detection resistor used to provide the second detection voltage based on the output current, which includes: a first terminal coupled to the second terminal of the secondary winding in the transformer and a second ground potential; and a second terminal coupled to the output voltage; and A comparator, used to output the corresponding third detection voltage based on the magnitude relationship between the second detection voltage and a reference voltage, which includes: a first input terminal coupled to the second terminal of the detection resistor to receive the second detection voltage; a second input terminal coupled to the reference voltage; and An output terminal is used to output the third detection voltage. The power supply circuit as claimed in claim 1, wherein the transformer further includes an auxiliary side winding, which is disposed on the primary side and includes a third dotted end and a third non-dotted end for sensing the energy of the input voltage. To provide a power signal to supply the power required for the operation of the first control circuit. The power supply circuit as described in claim 5, which further includes: An auxiliary diode, which contains: an anode coupled to the third non-conducting end of the auxiliary winding in the transformer; and a cathode coupled to the first control circuit; and An auxiliary capacitor, which contains: a first terminal coupled to the cathode of the auxiliary diode; and A second terminal is coupled to the first ground potential. The power supply circuit of claim 1, further comprising a magnetizing inductor coupled between the first dotting end and the first non-dotting end of the primary side winding. The power supply circuit of claim 1, further comprising an input capacitor coupled between the first node of the primary side winding and the first ground potential. The power supply circuit as described in claim 1, which further includes An output diode containing: an anode coupled to the second non-dominating end of the secondary side winding; and a cathode coupled to the steady-state current circuit; and An output capacitor consisting of: a first terminal coupled between the cathode of the output diode and the steady-state current circuit; and A second terminal is coupled to the second terminal of the secondary side winding. The power supply circuit of claim 1 further includes a rectifier coupled to the transformer for converting an AC power supply from a commercial power supply into the input voltage.

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