CN113839566A

CN113839566A - Power supply device for eliminating overcurrent protection misoperation

Info

Publication number: CN113839566A
Application number: CN202010591704.6A
Authority: CN
Inventors: 詹子增
Original assignee: Acer Inc
Current assignee: Acer Inc
Priority date: 2020-06-24
Filing date: 2020-06-24
Publication date: 2021-12-24
Anticipated expiration: 2040-06-24
Also published as: CN113839566B

Abstract

A power supply for eliminating overcurrent protection malfunction comprises: the power converter comprises a first transformer, a power switcher, an output stage circuit, a detection circuit, a feedback compensation circuit, a pulse width modulation integrated circuit, a second transformer and a control circuit. The first transformer generates an induced potential according to an input potential. The output stage circuit generates an output current according to the induced potential. The detection circuit can monitor the output current and generate a detection potential according to the output current. The feedback compensation circuit includes a linear optical coupler and a voltage regulator. The feedback compensation circuit can generate a coupling current. The second transformer generates a control potential according to the coupling current. The control circuit selectively enables or disables the linear optical coupler and the voltage stabilizer according to the detection potential and the control potential.

Description

Power supply device for eliminating overcurrent protection misoperation

Technical Field

The present invention relates to a power supply, and more particularly to a power supply capable of eliminating over-current protection malfunction.

Background

The conventional power supply usually includes a feedback compensation circuit and an overcurrent protection detection circuit, however, when the output current is too large and triggers the overcurrent protection mechanism, the feedback compensation circuit often accidentally participates and causes malfunction, so that the waveform of the output potential oscillates up and down. In view of the above, a new solution is proposed to overcome the dilemma faced by the prior art.

Disclosure of Invention

In a preferred embodiment, the present invention provides a power supply for eliminating overcurrent protection malfunction, comprising: a first transformer, including a first primary winding and a first secondary winding, wherein the first primary winding is used for receiving an input potential, and the first secondary winding is used for generating an induced potential; a power switch for selectively coupling the first primary winding to a ground potential; an output stage circuit for generating an output current according to the induced potential; a detection circuit for monitoring the output current and generating a detection potential according to the output current; a feedback compensation circuit, coupled to the output stage circuit, for generating a feedback potential and a coupling current, wherein the feedback compensation circuit comprises a linear optical coupler and a voltage stabilizer; a pulse width modulation integrated circuit for generating a pulse width modulation potential according to the feedback potential; a second transformer including a second primary winding for receiving the coupling current and a second secondary winding for generating a control potential; and a control circuit for selectively enabling or disabling the linear optocoupler and the voltage regulator according to the detection potential and the control potential.

Drawings

Fig. 1 is a schematic diagram illustrating a power supply according to an embodiment of the invention.

Fig. 2 is a schematic diagram illustrating a power supply according to an embodiment of the invention.

Fig. 3 is a waveform diagram showing the potential of a conventional power supply.

FIG. 4 is a diagram showing a potential waveform of the power supply according to an embodiment of the invention.

Description of reference numerals:

100,200: power supply

110,210: first transformer

111,211: a first main coil

112,212: first secondary coil

120,220: power switcher

130,230: output stage circuit

140,240: detection circuit

150,250: feedback compensation circuit

152,252: linear optical coupler

154,254: voltage stabilizer

160,260: pulse width modulation integrated circuit

170,270: second transformer

171,271: second main coil

172,272: second sub-coil

180,280: control circuit

242: amplifier with a high-frequency amplifier

262: error amplifier

264: comparator with a comparator circuit

390: first dotted line frame

490: second dotted line frame

C1: first capacitor

C2: second capacitor

C3: third capacitor

C4: fourth capacitor

C5: fifth capacitor

C6: sixth capacitor

D1: first diode

D2: second diode

DL: light emitting diode

IOUT: output current

IP: coupling current

M1: a first transistor

M2: second transistor

M3: a third transistor

N1: first node

N2: second node

N3: third node

N4: fourth node

N5: the fifth node

N6: sixth node

N7: seventh node

N8: eighth node

N9: the ninth node

N10: the tenth node

N11: eleventh node

N12: the twelfth node

N13: thirteenth node

N14: fourteenth node

N15: fifteenth node

NCM: common node

NIN: input node

NOUT: output node

Q1: bipolar junction transistor

R1: a first resistor

R2: second resistor

R3: third resistor

R4: fourth resistor

R5: fifth resistor

R6: sixth resistor

R7: seventh resistor

R8: eighth resistor

R9: ninth resistor

VC: controlling electric potential

VD: detecting electric potential

VF: feedback potential

VIN: input potential

VM: pulse width modulated potential

VOUT: output potential

VR: reference potential

VS: induced potential

VSS: ground potential

VT: potential of triangular wave

Detailed Description

In order to make the objects, features and advantages of the present invention comprehensible, specific embodiments accompanied with figures are described in detail below.

Certain terms are used throughout the description and the following claims to refer to particular components. As one skilled in the art will appreciate, manufacturers may refer to a component by different names. The present specification and the related application do not intend to distinguish between components that differ in name but not function. In the following description and in the claims, the terms "include" and "comprise" are used in an open-ended fashion, and thus should be interpreted to mean "include, but not limited to. The term "substantially" means within an acceptable error range, within which a person skilled in the art can solve the technical problem to achieve the basic technical result. In addition, the term "coupled" is used herein to encompass any direct or indirect electrical connection. Thus, if a first device couples to a second device, that connection may be through a direct electrical connection, or through an indirect electrical connection via other devices and connections.

Fig. 1 is a schematic diagram illustrating a power supply 100 according to an embodiment of the invention. For example, the power supply 100 may be applied to a desktop computer, a notebook computer, or an integrated computer. As shown in fig. 1, the power supply 100 includes: a first transformer 110, a power switch 120, an output stage circuit 130, a detection circuit 140, a feedback compensation circuit 150, a pwm ic 160, a second transformer 170, and a control circuit 180. It should be noted that, although not shown in fig. 1, the power supply 100 may also include other components, such as: a voltage regulator or (and) a negative feedback circuit.

The first transformer 110 includes a first primary winding 111 and a first secondary winding 112, wherein the first primary winding 111 may be located on one side of the first transformer 110, and the first secondary winding 112 may be located on the opposite side of the first transformer 110. The first primary winding 111 receives an input voltage VIN, and in response to the input voltage VIN, the first secondary winding 112 generates an induced voltage VS. The input potential VIN may be derived from an external input power source, wherein the input potential VIN may have any frequency and any amplitude. For example, the frequency of the input potential VIN may be about 50Hz or 60Hz, and the root-mean-square value of the input potential VIN may be about 110V or 220V, but is not limited thereto. The power switch 120 selectively couples the first primary winding 111 to a ground potential VSS (e.g., 0V). The output stage circuit 130 generates an output current IOUT according to the sensing potential VS. The detection circuit 140 monitors the output current IOUT and generates a detection potential VD according to the output current IOUT. In some embodiments, the output stage circuit 130 further generates an output voltage VOUT, which can be further transmitted to an electronic device. The feedback compensation circuit 150 is coupled to the output stage circuit 130 and generates a feedback potential VF and a coupling current IP, wherein the feedback compensation circuit 150 includes a linear optical coupler 152 and a voltage regulator 154. The pwm ic 160 generates a pwm potential VM according to the feedback potential VF. The second transformer 170 includes a second primary winding 171 and a second secondary winding 172, wherein the second primary winding 171 may be located on one side of the second transformer 170, and the second secondary winding 172 may be located on the opposite side of the second transformer 170. The second primary winding 171 receives the coupling current IP, and the second secondary winding 172 generates a control potential VC in response to the coupling current IP. The control circuit 180 selectively enables or disables the optocoupler 152 and the regulator 154 according to the detection voltage VD and the control voltage VC. In some embodiments, if the output current IOUT has not reached a threshold, the control circuit 180 will enable the linear optocoupler 152 and the voltage regulator 154 simultaneously; conversely, if the output current IOUT has reached the threshold value, the control circuit 180 disables the linear optocoupler 152 and the voltage regulator 154. In this design, during the implementation of the over-current protection mechanism, the linear optocoupler 152 and the voltage regulator 154 of the feedback compensation circuit 150 are both disabled by the control circuit 180, so that the feedback compensation circuit 150 can be effectively prevented from participating in the over-current protection mechanism. Therefore, the present invention can completely eliminate the overcurrent protection malfunction and improve the output stability of the power supply 100.

The following embodiments will describe the detailed structure and operation of the power supply 100. It must be understood that these drawings and descriptions are only exemplary and are not intended to limit the scope of the present invention.

Fig. 2 is a schematic diagram illustrating a power supply 200 according to an embodiment of the invention. In the embodiment of fig. 2, the power supply 200 has an input node NIN and an output node NOUT, and includes a first transformer 210, a power switch 220, an output stage circuit 230, a detection circuit 240, a feedback compensation circuit 250, a pwm ic 260, a second transformer 270, and a control circuit 280. The input node NIN of the power supply 200 can receive an input voltage VIN from an external input power source, and the output node NOUT of the power supply 200 can output an output voltage VOUT to an electronic device.

The first transformer 210 includes a first primary winding 211 and a first secondary winding 212, wherein the first primary winding 211 may be located on one side of the first transformer 210, and the first secondary winding 212 may be located on the opposite side of the first transformer 210. A first terminal of the first primary winding 211 is coupled to the input node NIN, and a second terminal of the first primary winding 211 is coupled to a first node N1. In some embodiments, the power switch 220 selectively couples the first node N1 to a ground potential VSS (e.g., 0V) according to a PWM potential VM. For example, if the pwm potential VM is at a high logic level, the power switch 220 couples the first node N1 to the ground potential VSS (i.e., the power switch 220 may approximate a short-circuit path); on the other hand, if the pwm potential VM is at the low logic level, the power switch 220 does not couple the first node N1 to the ground potential VSS (i.e., the power switch 220 may approximate an open circuit path). The first end of the first secondary winding 212 is coupled to a second node N2 for outputting a sensing potential VS, and the second end of the first secondary winding 212 is coupled to a third node N3.

The output stage circuit 230 includes a first diode D1 and a first capacitor C1. The anode of the first diode D1 is coupled to the second node N2 for receiving the sensing potential VS, and the cathode of the first diode D1 is coupled to the output node NOUT. A first terminal of the first capacitor C1 is coupled to the output node NOUT, and a second terminal of the first capacitor C1 is coupled to a common node NCM to output an output current IOUT.

The detection circuit 240 includes an amplifier 242, a first resistor R1, a second resistor R2, a second capacitor C2, and a third capacitor C3. A first end of the first resistor R1 is coupled to the third node N3, and a second end of the first resistor R1 is coupled to the common node NCM to receive the output current IOUT. A first terminal of the second capacitor C2 is coupled to the third node N3, and a second terminal of the second capacitor C2 is coupled to the common node NCM. The positive input of the amplifier 242 is coupled to the common node NCM, the negative input of the amplifier 242 is coupled to the third node N3, and the output of the amplifier 242 is coupled to a fourth node N4. The first terminal of the second resistor R2 is coupled to a fifth node N5 to output a detection potential VD, and the second terminal of the second resistor R2 is coupled to the fourth node N4. A first terminal of the third capacitor C3 is coupled to the fifth node N5, and a second terminal of the third capacitor C3 is coupled to the common node NCM. When the output current IOUT flows through the first resistor R1, the amplifier 242 first amplifies a potential difference between the first terminal and the second terminal of the first resistor R1, and then the detection circuit 240 generates the detection potential VD corresponding to the output current IOUT accordingly.

The feedback compensation circuit 250 includes a linear optocoupler 252, a voltage regulator 254, a third resistor R3, a fourth resistor R4, a fifth resistor R5, a sixth resistor R6, a fourth capacitor C4, a fifth capacitor C5, and a sixth capacitor C6. The first terminal of the third resistor R3 is coupled to the output node NOUT, and the second terminal of the third resistor R3 is coupled to a sixth node N6. In some embodiments, linear optocoupler 252 is implemented by a PC817 electronic component. The linear photo coupler 252 includes a light emitting diode DL and a bipolar junction transistor Q1. The anode of the light emitting diode DL is coupled to the sixth node N6, and the cathode of the light emitting diode DL is coupled to a seventh node N7. The collector of the bjt Q1 is coupled to an eighth node N8 to output a feedback potential FB, and the emitter of the bjt Q1 is coupled to a ninth node N9 to output a coupling current IP. A first terminal of the fourth capacitor C4 is coupled to the eighth node N8, and a second terminal of the fourth capacitor C4 is coupled to the ground potential VSS. The first terminal of the fifth capacitor C5 is coupled to the seventh node N7, and the second terminal of the fifth capacitor C5 is coupled to a tenth node N10. The first end of the fourth resistor R4 is coupled to the seventh node N7, and the second end of the fourth resistor R4 is coupled to an eleventh node N11. A first terminal of the sixth capacitor C6 is coupled to the eleventh node N11, and a second terminal of the sixth capacitor C6 is coupled to the tenth node N10. A first terminal of the fifth resistor R5 is coupled to the output node NOUT, and a second terminal of the fifth resistor R5 is coupled to the tenth node N10. A first end of the sixth resistor R6 is coupled to the tenth node N10, and a second end of the sixth resistor R6 is coupled to the common node NCM. In some embodiments, voltage regulator 254 is implemented by a TL431 electronic component. The anode of the voltage regulator 254 is coupled to a twelfth node N12, the cathode of the voltage regulator 254 is coupled to a seventh node N7, and the reference terminal of the voltage regulator 254 is coupled to a tenth node N10.

The pwm ic 260 includes an error amplifier 262 and a comparator 264. The positive input of the error amplifier 262 is coupled to receive a reference potential VR, the negative input of the error amplifier 262 is coupled to the eighth node N8 for receiving the feedback potential VF, and the output of the error amplifier 262 is coupled to a thirteenth node N13. The positive input terminal of the comparator 264 is for receiving a triangular wave potential VT, the negative input terminal of the comparator 264 is coupled to the thirteenth node N13, and the output terminal of the comparator 264 is for outputting the pwm potential VM. The output pwm potential VM may be used to adjust the duty cycle of the power switch 220.

The second transformer 270 includes a second primary winding 271, a second secondary winding 272, and a seventh resistor R7, wherein the second primary winding 271 and the seventh resistor R7 can be located on the same side of the second transformer 270, and the second secondary winding 272 can be located on the opposite side of the second transformer 270. A first terminal of the seventh resistor R7 is coupled to the ninth node N9 for receiving the coupling current IP, and a second terminal of the seventh resistor R7 is coupled to the ground potential VSS. A first end of the second main coil 271 is coupled to the ninth node N9, and a second end of the second main coil 271 is coupled to the ground potential VSS. The first terminal of the second sub-winding 272 is coupled to a fourteenth node N14 for outputting a control potential VC, and the second terminal of the second sub-winding 272 is coupled to the common node NCM. A potential difference between the first terminal and the second terminal of the seventh resistor R7 is proportional to the magnitude of the coupling current IP. Therefore, if the coupling current IP becomes large, the control potential VC will rise; conversely, if the coupling current IP is reduced, the control potential VC is lowered.

The control circuit 280 includes a first transistor M1, a second transistor M2, a second diode D2, an eighth resistor R8, and a ninth resistor R9. The first transistor M1 and the second transistor M2 may each be an nmos fet-first transistor M1 having a control terminal coupled to the fourteenth node N14 for receiving the control voltage VC, a first terminal of the first transistor M1 coupled to the common node NCM, and a second terminal of the first transistor M1 coupled to the twelfth node N12. An anode of the second diode D2 is coupled to the output node NOUT, and a cathode of the second diode D2 is coupled to the sixth node N6. The first terminal of the eighth resistor R8 is coupled to a fifteenth node N15, and the second terminal of the eighth resistor R8 is coupled to the fifth node N5 for receiving the detection potential VD. A control terminal of the second transistor M2 is coupled to the fifteenth node N15, a first terminal of the second transistor M2 is coupled to the seventh node N7, and a second terminal of the second transistor M2 is coupled to the sixth node N6. A first end of the ninth resistor R9 is coupled to the seventh node N7, and a second end of the ninth resistor R9 is coupled to the fifth node N5. In some embodiments, the resistance value of the ninth resistor R9 is at least 2 times greater than the resistance value of the eighth resistor R8.

In some embodiments, the power switch 220 includes a third transistor M3. The third transistor M3 may be an nmos fet. The control terminal of the third transistor M3 is for receiving the pwm potential VM, the first terminal of the third transistor M3 is coupled to the ground potential VSS, and the second terminal of the third transistor M3 is coupled to the first node N1.

In some embodiments, the power supply 200 can operate in a normal mode or a protection mode, and the operation principle thereof will be described as follows.

In the normal mode, the output current IOUT has not reached a threshold value, so the detection circuit 240 generates a relatively low detection voltage VD to turn off the second transistor M2. At this time, the linear photo-coupler 252 is enabled, wherein the photodiode DL generates a light, so that the bjt Q1 senses and outputs the coupling current IP. In response to the coupling current IP, the second transformer 270 generates a relatively high control voltage VC to enable the first transistor M1, so that the voltage regulator 254 is also enabled.

In the protection mode, the output current IOUT has reached the threshold value, so the detection circuit 240 generates a relatively high detection potential VD to activate the second transistor M2. At this time, since the second transistor M2 forms a short circuit path, the linear photo coupler 252 is disabled, the photodiode DL cannot generate any light, and the bjt Q1 cannot output the coupling current IP. Thus, the second transformer 270 generates a relatively low control voltage VC to turn off the first transistor M1, so the voltage regulator 254 is also disabled. In other words, the feedback compensation circuit 250 will not participate in the over-current protection mechanism of the power supply 200. In addition, since the bjt Q1 cannot generate the feedback potential VF, the pwm ic 260 will stop outputting the pwm potential VM, which will cause the power supply 200 and the power switch 220 to turn off synchronously.

FIG. 3 is a diagram showing a potential waveform of a conventional power supply, in which the horizontal axis represents time and the vertical axis represents a potential level or a current value. If the second transformer 270 and the control circuit 280 are not used, the waveform of the output voltage VOUT of the conventional power supply oscillates up and down during the implementation of the overcurrent protection mechanism (as shown by a first dashed line box 390), which is caused by the feedback compensation circuit accidentally participating in the overcurrent protection malfunction.

Fig. 4 is a diagram showing potential waveforms of the power supply 200 according to an embodiment of the invention, in which the horizontal axis represents time and the vertical axis represents potential level or current value. According to the measurement results of fig. 4, if the second transformer 270 and the control circuit 280 are used, the linear optocoupler 252 and the voltage regulator 254 of the feedback compensation circuit 250 are temporarily disabled during the implementation of the overcurrent protection mechanism, so that the overcurrent protection malfunction can be completely eliminated (as shown by a second dashed box 490).

In some embodiments, the component parameters of the power supply 200 may be as follows. The first resistor R1 may have a resistance value between 0.99m Ω and 1.01m Ω, and preferably may be 1m Ω. The resistance value of the second resistor R2 may be between 9.9 Ω and 10.1 Ω, and preferably may be 10 Ω. The resistance value of the third resistor R3 may be between 9.5K Ω and 10.5K Ω, and preferably may be 10K Ω. The resistance value of the fourth resistor R4 may be between 44.65K Ω to 49.35K Ω, and may preferably be 47K Ω. The resistance value of the fifth resistor R5 may be between 66.31K Ω and 73.29K Ω, and may preferably be 69.8K Ω. The resistance value of the sixth resistor R6 may be between 9.69K Ω and 10.71K Ω, and preferably may be 10.2K Ω. The resistance value of the seventh resistor R7 may be between 14.25K Ω and 15.75K Ω, and may preferably be 15K Ω. The resistance value of the eighth resistor R8 may be between 0.99K Ω and 1.01K Ω, and preferably may be 1K Ω. The resistance value of the ninth resistor R9 may be between 2.48K Ω and 2.53K Ω, and preferably may be 2.5K Ω. The capacitance of the first capacitor C1 may be between 2850 μ F and 3150 μ F, and preferably may be 3000 μ F. The second capacitor C2 may have a capacitance value between 0.99 μ F and 1.01 μ F, and preferably may be 1 μ F. The capacitance of the third capacitor C3 may be between 0.99 μ F and 1.01 μ F, and preferably may be 1 μ F. The capacitance of the fourth capacitor C4 may be between 99pF and 101pF, and preferably may be 100 pF. The capacitance value of the fifth capacitor C5 may be between 1.49nF and 1.51nF, and may preferably be 1.5 nF. The capacitance value of the sixth capacitor C6 may be between 46.53nF and 47.47nF, and may preferably be 47 nF. The ratio of the number of turns of the first main coil 211 to the first sub-coil 212 may be between 5 and 100, and preferably may be 20. The ratio of the number of turns of the second primary winding 271 to the second secondary winding 272 may be between 0.01 and 1, and preferably may be 0.1. The phase margin of the power supply 200 may be greater than 45 degrees, while the gain margin of the power supply 200 may be greater than-10 dB. The above parameter ranges are derived from a plurality of experimental results, which are helpful for optimizing the output stability of the power supply 200.

The present invention provides a novel power supply, which includes a control circuit to selectively enable or disable a feedback compensation circuit. According to the actual measurement result, the power supply using the design can completely eliminate the overcurrent protection malfunction. The invention can further improve the output stability of the power supply, so the invention is suitable for various devices.

It should be noted that the above-mentioned potential, current, resistance, inductance, capacitance, and other device parameters are not limitations of the present invention. The designer can adjust these settings according to different needs. The power supply of the present invention is not limited to the states illustrated in fig. 1 to 4. The present invention may include only any one or more features of any one or more of the embodiments of fig. 1-4. In other words, not all illustrated features may be implemented in a power supply of the present invention. Although the embodiments of the present invention use mosfet as an example, the present invention is not limited thereto, and other kinds of transistors can be used by those skilled in the art, such as: junction field effect transistors, fin field effect transistors, etc., without affecting the effect of the present invention.

Although the present invention has been described with reference to the preferred embodiments, it should be understood that various changes and modifications can be made therein by those skilled in the art without departing from the spirit and scope of the invention as defined in the appended claims.

Claims

1. A power supply for eliminating overcurrent protection malfunction comprises:

a first transformer, including a first primary winding and a first secondary winding, wherein the first primary winding is used for receiving an input potential, and the first secondary winding is used for generating an induced potential;

a power switch for selectively coupling the first primary winding to a ground potential;

an output stage circuit for generating an output current according to the induced potential;

a detection circuit for monitoring the output current and generating a detection potential according to the output current;

a feedback compensation circuit, coupled to the output stage circuit, for generating a feedback potential and a coupling current, wherein the feedback compensation circuit comprises a linear optical coupler and a voltage stabilizer;

a pulse width modulation integrated circuit for generating a pulse width modulation potential according to the feedback potential;

a second transformer including a second primary winding for receiving the coupling current and a second secondary winding for generating a control potential; and

and the control circuit selectively enables or disables the linear optical coupler and the voltage stabilizer according to the detection potential and the control potential.

2. The power supply of claim 1, wherein the first primary winding has a first end and a second end, the first end of the first primary winding is coupled to an input node for receiving the input potential, the second end of the first primary winding is coupled to a first node, the power switch selectively couples the first node to the ground potential according to the pwm potential, the first secondary winding has a first end and a second end, the first end of the first secondary winding is coupled to a second node for outputting the induced potential, and the second end of the first secondary winding is coupled to a third node.

3. The power supply of claim 2, wherein the output stage circuit comprises:

a first diode having an anode and a cathode, wherein the anode of the first diode is coupled to the second node for receiving the sensing potential, and the cathode of the first diode is coupled to an output node; and

a first capacitor having a first terminal and a second terminal, wherein the first terminal of the first capacitor is coupled to the output node, and the second terminal of the first capacitor is coupled to a common node to output the output current.

4. The power supply of claim 3, wherein the detection circuit comprises:

a first resistor having a first end and a second end, wherein the first end of the first resistor is coupled to the third node and the second end of the first resistor is coupled to the common node to receive the output current;

a second capacitor having a first terminal and a second terminal, wherein the first terminal of the second capacitor is coupled to the third node and the second terminal of the second capacitor is coupled to the common node;

an amplifier having a positive input terminal, a negative output terminal, and an output terminal, wherein the positive input terminal of the amplifier is coupled to the common node, the negative input terminal of the amplifier is coupled to the third node, and the output terminal of the amplifier is coupled to a fourth node;

a second resistor having a first end and a second end, wherein the first end of the second resistor is coupled to a fifth node for outputting the detection potential, and the second end of the second resistor is coupled to the fourth node; and

a third capacitor having a first terminal and a second terminal, wherein the first terminal of the third capacitor is coupled to the fifth node and the second terminal of the third capacitor is coupled to the common node.

5. The power supply of claim 4, wherein the feedback compensation circuit comprises:

a third resistor having a first end and a second end, wherein the first end of the third resistor is coupled to the output node and the second end of the third resistor is coupled to a sixth node;

wherein the linear photo coupler comprises a light emitting diode and a bipolar junction transistor, the light emitting diode has an anode and a cathode, the anode of the light emitting diode is coupled to the sixth node, the cathode of the light emitting diode is coupled to a seventh node, the bipolar junction transistor has a collector and an emitter, the collector of the bipolar junction transistor is coupled to an eighth node to output the feedback potential, and the emitter of the bipolar junction transistor is coupled to a ninth node to output the coupling current;

a fourth capacitor having a first terminal and a second terminal, wherein the first terminal of the fourth capacitor is coupled to the eighth node and the second terminal of the fourth capacitor is coupled to the ground potential;

a fifth capacitor having a first terminal and a second terminal, wherein the first terminal of the fifth capacitor is coupled to the seventh node and the second terminal of the fifth capacitor is coupled to a tenth node;

a fourth resistor having a first end and a second end, wherein the first end of the fourth resistor is coupled to the seventh node and the second end of the fourth resistor is coupled to an eleventh node;

a sixth capacitor having a first terminal and a second terminal, wherein the first terminal of the sixth capacitor is coupled to the eleventh node and the second terminal of the sixth capacitor is coupled to the tenth node;

a fifth resistor having a first end and a second end, wherein the first end of the fifth resistor is coupled to the output node and the second end of the fifth resistor is coupled to the tenth node; and

a sixth resistor having a first end and a second end, wherein the first end of the sixth resistor is coupled to the tenth node and the second end of the sixth resistor is coupled to the common node;

the voltage regulator has an anode, a cathode, and a reference terminal, the anode of the voltage regulator is coupled to a twelfth node, the cathode of the voltage regulator is coupled to the seventh node, and the reference terminal of the voltage regulator is coupled to the tenth node.

6. The power supply of claim 5, wherein the pulse width modulation integrated circuit comprises:

an error amplifier having a positive input terminal, a negative input terminal, and an output terminal, wherein the positive input terminal of the error amplifier is used for receiving a reference potential, the negative input terminal of the error amplifier is coupled to the eighth node for receiving the feedback potential, and the output terminal of the error amplifier is coupled to a thirteenth node; and

a comparator having a positive input terminal, a negative input terminal, and an output terminal, wherein the positive input terminal of the comparator is used for receiving a triangular wave potential, the negative input terminal of the comparator is coupled to the thirteenth node, and the output terminal of the comparator is used for outputting the pwm potential.

7. The power supply of claim 5, wherein the second transformer further comprises a seventh resistor, the seventh resistor having a first end and a second end, the first end of the seventh resistor being coupled to the ninth node for receiving the coupling current, the second end of the seventh resistor being coupled to the ground potential, the second primary winding having a first end and a second end, the first end of the second primary winding being coupled to the ninth node, the second end of the second primary winding being coupled to the ground potential, the second secondary winding having a first end and a second end, the first end of the second secondary winding being coupled to a fourteenth node for outputting the control potential, and the second end of the second secondary winding being coupled to the common node.

8. The power supply of claim 7, wherein the control circuit comprises:

a first transistor having a control terminal, a first terminal, and a second terminal, wherein the control terminal of the first transistor is coupled to the fourteenth node for receiving the control potential, the first terminal of the first transistor is coupled to the common node, and the second terminal of the first transistor is coupled to the twelfth node.

9. The power supply of claim 8, wherein the control circuit further comprises:

a second diode having an anode and a cathode, wherein the anode of the second diode is coupled to the output node and the cathode of the second diode is coupled to the sixth node;

an eighth resistor having a first end and a second end, wherein the first end of the eighth resistor is coupled to a fifteenth node, and the second end of the eighth resistor is coupled to the fifth node for receiving the detection potential;

a second transistor having a control terminal, a first terminal, and a second terminal, wherein the control terminal of the second transistor is coupled to the fifteenth node, the first terminal of the second transistor is coupled to the seventh node, and the second terminal of the second transistor is coupled to the sixth node; and

a ninth resistor having a first end and a second end, wherein the first end of the ninth resistor is coupled to the seventh node and the second end of the ninth resistor is coupled to the fifth node;

wherein the resistance value of the ninth resistor is at least 2 times greater than the resistance value of the eighth resistor.

10. The power supply of claim 9, wherein if the output current has not reached a threshold, the detection potential is relatively low to turn off the second transistor, and the control potential is relatively high to turn on the first transistor, such that both the linear optocoupler and the regulator are enabled;

wherein if the output current has reached the threshold value, the detection potential is relatively high to turn on the second transistor, and the control potential is relatively low to turn off the first transistor, such that both the linear optocoupler and the regulator are disabled.