TW202414939A - Power supply capable of providing over-current protection for dynamic loading - Google Patents

Abstract

A power supply is coupled to a load and includes a rectifier, a transformer, a snubber circuit, a protection circuit, a voltage detecting circuit, and a path control circuit. The rectifier converts AC voltage provided by mains electricity into an input voltage. The transformer converts the input voltage into an output voltage for driving the load. The voltage detecting circuit provides a feedback voltage associated with the output voltage. When the power supply is connected to the mains electricity but the output voltage has not been established, the path control circuit deactivates the protection circuit. When determining that the output voltage has been established according to the feedback voltage, the path control circuit activates t the protection circuit for providing over-current protection.

Description

Power supply providing over-current protection under dynamic load changes

The present invention relates to a power supply capable of providing over-current protection, and in particular to a power supply capable of providing over-current protection under high dynamic load variation.

Different components in a computer system require different operating voltages, so a power supply is commonly used to convert the alternating current (AC) indoor power supply into direct current (DC) to drive different components by means of transformation, rectification and filtering. A power supply under a traditional flyback architecture uses a power switch to control the primary side path of the transformer, and a rectifier switch to control the secondary side path of the transformer. When the power switch is turned on, the input electrical energy is converted into magnetic energy and stored in the transformer. At this time, the rectifier switch is turned off to isolate the output path; when the power switch is turned off, the energy stored in the transformer is released to the output end through the turned-on rectifier switch, and an output capacitor is used to smooth the power output to drive a load device. Power supplies usually use disposable fuses to provide over-current protection. When the current exceeds the amount that the wire can withstand, the fuse will melt to cut off the current, thereby preventing the components of the load device from being damaged.

When the power supply is coupled to the load device but not connected to the mains, the load device will operate in DC mode, and the power required for its operation can be supplied by the built-in battery. When the power supply is coupled to the load device and connected to the mains, the load device will operate in AC mode, and the power required for its operation can be supplied by the output voltage provided by the power supply. When switching from DC mode to AC mode, the high dynamic load change of the load device will cause a huge instantaneous surge current in the power supply, causing its fuse to burn out, making the power supply permanently damaged and unable to operate. Therefore, a power supply that can provide overcurrent protection under dynamic load changes is needed.

The present invention provides a power supply for providing overcurrent protection under dynamic load variation, which comprises a first input terminal, a second input terminal, a first output terminal, a second output terminal, a rectifier, a transformer, a switch, a buffer circuit, a protection circuit, a voltage detection circuit, a path control circuit and a control circuit. The first input terminal and the second input terminal are used to receive an alternating current power source provided by a mains supply terminal, and the first output terminal and the second output terminal are coupled to a load device to output an output voltage to drive the load device. The rectifier is used to convert the alternating current power source into an input voltage. The transformer is used to induce the energy of the input voltage from a primary side to a secondary side to supply the output voltage, and includes a primary side winding and a secondary side winding, wherein the primary side winding is arranged on the primary side and includes a first hit terminal and a second non-hit terminal, and the secondary side winding is arranged on the secondary side and includes a second hit terminal and a second non-hit terminal. The first end of the switch is coupled to the first non-hit terminal of the primary side winding in the transformer, the second end is coupled to a ground potential, and the control end is used to receive a first control signal switching between a first enabling potential and a first disabling potential. The buffer circuit is coupled between the first input terminal and the rectifier to buffer the influence of a surge current. The protection circuit is used to provide current protection on the primary side. The voltage detection circuit is arranged on the secondary side to provide a feedback voltage related to the output voltage. The path control circuit is used to cut off the loop of the protection circuit after the power supply is coupled to the mains supply terminal but before the output voltage is established; and to activate the loop of the protection circuit after receiving a second control signal with a second enabling potential. The control circuit is arranged on the primary side, and is used to provide the first control signal through a first pin, and adjust the duty cycle of the first control signal according to the value of the feedback voltage; when it is determined that the output voltage has been established according to the value of the feedback voltage, the second control signal with the second enable potential is output to the path control circuit through a second pin; and the feedback voltage is received through a third pin.

FIG. 1 and FIG. 2 are functional block diagrams of an electronic system 300 in an embodiment of the present invention. The electronic system 300 includes a power supply 100 and a load device 200. The power supply 100 can be coupled to the load device 200 through a transmission interface to perform data transmission or power transmission (power delivery). In the embodiment shown in FIG. 1 and FIG. 2, the power supply 200 can be coupled to a socket JACK1 on the load device 200 through a connector PLUG1, wherein the connector PLUG1 includes a power pin PD1, a ground pin G1 and a detection pin T1, and the socket JACK1 includes a power pin PD2, a ground pin G2 and a detection pin T2. However, the implementation of the transmission interface between the power supply 100 and the load device 200 does not limit the scope of the present invention.

The load device 200 includes an embedded controller (EC) 210, a charger IC 220, and a built-in battery 230. The embedded controller 210 is used to control peripheral devices and the Advanced Configuration and Power Interface (ACPI), and with hardware detection of information such as motherboard temperature, fan speed, and output voltage V _OUT of the power supply 100, it can effectively distribute power to system components and provide appropriate operating frequency to achieve the goal of both power saving and efficiency. The charging integrated circuit 220 can manage the power supply of the load device 200 and charge the built-in battery 230 according to the output voltage V _OUT provided by the power supply 100 , the system voltage required for the operation of the load device 200 , and the voltage V _BAT provided by the built-in battery 230 .

In the embodiment shown in FIG. 1 , the power supply 100 is not connected to the mains. At this time, the load device 200 operates in a DC mode, and the power required for its operation can be supplied by the voltage V _BAT provided by the built-in battery 230 .

In the embodiment shown in FIG. 2 , the power supply 200 can be connected to a mains supply terminal through a transmission interface to receive AC power V _AC supplied by the mains. The mains supply terminal can include a socket JACK2, and the power supply 100 can be connected to the socket JACK2 through a connector PLUG2, wherein the socket JACK2 includes a live pin L1 and a neutral pin N1, and the connector PLUG2 includes a live pin L2 and a neutral pin N2. However, the implementation of the transmission interface between the power supply 100 and the mains supply terminal does not limit the scope of the present invention.

The power supply 100 can convert the AC power V _AC provided by the mains supply into an output voltage V _OUT , and then transmit the output voltage V _OUT to the power pin PD2 of the socket JACK1 through the power pin PD1 of the connector PLUG1. At this time, the load device 200 will operate in the AC mode, and the power required for its operation can be supplied by the output voltage V _OUT provided by the power supply 100.

FIG. 3 is a functional block diagram of a power supply 100 in an embodiment of the present invention. The power supply 100 includes a power switch Q1, energy storage capacitors C1 and C2, an output diode DO, an exciting inductor LM, a transformer TR, a buffer circuit 10, a protection circuit 20, a path control circuit 30, a rectifier 40, a voltage detection circuit 50, and a control circuit 60. The power switch Q1, the energy storage capacitor C1, the magnetizing inductor LM, the buffer circuit 10, the protection circuit 20, the path control circuit 30, the rectifier 40 and the control circuit 60 are arranged on the primary side of the transformer TR, while the energy storage capacitor C2, the output diode D0 and the voltage detection circuit 50 are arranged on the secondary side of the transformer TR.

The power supply circuit 100 can convert the AC voltage V _AC supplied by the mains into the output voltage V _OUT to drive the load device 200. The buffer circuit 10 can suppress the high-frequency oscillation caused by the surge current or voltage surge to avoid component damage. The protection circuit 20 is a disposable component used to protect the internal circuit of the load device 200. When the power supply circuit 100 fails or is abnormal and causes the current to abnormally increase to a certain level, the protection circuit 20 will melt itself to cut off the abnormal current to avoid damage to the internal components of the load device 200. When the power supply circuit 100 is just connected to the mains, the path control circuit 30 will be cut off to cut off the path of the energy of the AC power source V _AC being transmitted to the rectifier 40 through the protection circuit 20, so as to avoid the instantaneous high surge current causing the protection circuit 20 to melt. After receiving a control signal GD2 with an enable potential, the path control circuit 30 will be turned on, so that the energy of the AC power source V _AC can be transmitted to the rectifier 40 through the protection circuit 20 and the buffer circuit at the same time. At this time, the protection circuit 20 can provide over-current protection. The voltage detection circuit 50 can detect the state of the output voltage V _OUT and provide a corresponding feedback signal V _FB accordingly. The first control circuit 60 provides a control signal GD1 according to the feedback signal V _FB , so that the power switch Q1 can be switched between the on and off states at a high frequency, thereby periodically inducing the primary side energy of the transformer TR to the secondary side to provide the output voltage V _OUT .

FIG. 4 is a schematic diagram of the implementation of the power supply 100 of the present invention. In the present invention, the control circuit 60 may be a pulse width modulation (PWM) integrated circuit, which includes pins P1-P6. The control circuit 60 can output a control signal GD1 that switches between an enable potential and a disable potential at a specific duty cycle to the power switch Q1 through pin P1, output a control signal GD2 to the path control circuit 30 through pin P2, receive a feedback voltage V _FB provided by the voltage detection circuit 50 through pin P3, receive a detection voltage Vx provided by the path control circuit 30 through pins P4 and P5, and output a logic signal VL to the detection pin T1 of the connector PLUG2 through pin P6. In the present invention, the control circuit 60 can provide control signals GD1 and GD2 according to the feedback voltage V _FB of the output voltage V _OUT , and provide logic signal VL according to the detection voltage Vx. The operation details will be described in detail in the following content of the specification. However, the implementation of the control circuit 60 does not limit the scope of the present invention.

In the embodiment of the present invention, the buffer circuit 10 includes a capacitor CX, a resistor R1, and diodes DX1 and DX2. The first end of the capacitor CX is coupled to the live pin L2 of the connector PLUG2, and the second end is coupled to the resistor R1. The first end of the resistor R1 is coupled to the second end of the capacitor CX, and the second end is coupled to the diodes DX1 and DX2. The anode of the diode DX1 is coupled to the second end of the resistor R1, and the cathode is coupled to the rectifier 40. The anode of the diode DX2 is coupled to the rectifier 40, and the cathode is coupled to the second end of the resistor R1. Capacitor CX, resistor R1 and diode DX1 form a resistor-capacitor-diode snubber (RCD snubber), which can suppress high-frequency oscillation caused by surging current or voltage surge during the positive cycle of AC voltage V _AC . Capacitor CX, resistor R1 and diode DX2 form another resistor-capacitor-diode snubber, which can suppress high-frequency oscillation caused by surging current or voltage surge during the negative cycle of AC voltage V _AC . However, the implementation of the snubber circuit 10 does not limit the scope of the present invention.

In the embodiment of the present invention, the protection circuit 20 may include a fuse, which is usually made of a wire or sheet material with a low melting point. When the input current I _IN is too large, the fuse will generate high temperature and melt, resulting in an open circuit and interrupting the input current I _IN to prevent the internal components of the load device 200 from being damaged. However, the implementation of the protection circuit 20 does not limit the scope of the present invention.

In the embodiment of the present invention, the path control circuit 30 includes an auxiliary switch Q2 and resistors R2-R3. The first end of the auxiliary switch Q2 is coupled to the protection circuit 20, the second end is coupled to the resistor R2 and the pin P4 of the control circuit 60, and the control end is coupled to the pin P2 of the control circuit 60 through the resistor R3 to receive the control signal GD2. The first end of the resistor R2 is coupled to the second end of the auxiliary switch Q2 and the pin P4 of the control circuit 60, and the second end is coupled to the rectifier 40 and the pin P5 of the control circuit 60. The first end of the resistor R3 is coupled to the control end of the auxiliary switch Q2, and the second end is coupled to the pin P2 of the control circuit 60. The auxiliary switch Q2 is selectively turned on or off according to the control signal GD2, thereby activating or deactivating the over-current protection function of the protection circuit 20.

In the embodiment of the present invention, the rectifier 40 may be a bridge rectifier including diodes D1-D4 for converting the AC power V _AC supplied by the mains into the input voltage V _IN . However, the implementation of the rectifier 40 does not limit the scope of the present invention.

In the embodiment of the present invention, the voltage detection circuit 50 includes voltage divider resistors RD1 and RD2. The voltage divider resistors RD1 and RD2 are connected in series with each other and in parallel with the energy storage capacitor C2. A feedback voltage V _FB of the output voltage V _OUT can be established on the voltage divider resistor R2, where V _FB =V _OUT *RD2/(RD1+RD2). However, the implementation of the voltage detection circuit 50 does not limit the scope of the present invention.

In the embodiment of the present invention, the transformer TR includes a primary winding (indicated by the number of turns NP) and a secondary winding (indicated by the number of turns NS), wherein the primary winding NP is arranged on the primary side of the transformer TR, the secondary winding NS is arranged on the secondary side of the transformer TR, I _IN represents the input current flowing through the primary side, and I _OUT represents the output current flowing through the secondary side. The anode of the output diode DO is coupled to the non-pointing end of the secondary winding NS in the transformer TR, and the cathode is coupled to the power pin PD1 (output voltage V _OUT ) of the connector PLUG1. The first end of the energy storage capacitor C1 is coupled to the tapping terminal of the primary winding NP in the transformer TR, and the second end is coupled to a ground potential GND1, for storing the energy of the related input voltage V _IN . The first end of the energy storage capacitor C2 is coupled to the cathode of the output diode DO, and the second end is coupled to a ground potential GND2, for storing the energy of the related output voltage V _OUT . In addition, the tapping terminal of the secondary winding NS in the transformer TR is coupled to the ground potential GND2.

When the load device 200 is connected to the power supply 100, but the power supply 100 is not connected to the mains, the load device 200 operates in a DC mode (powered by a battery), at which time the power supply 100 does not operate, all switches are in the off state, and the control circuit 60 is closed.

After being connected to the mains supply, the power supply 100 can receive the AC power V _AC through the live pin L2 and the neutral pin N2 of the connector PLUG2. Since the initial state of the auxiliary switch Q2 is off, the loop of the protection circuit 20 is disconnected. Assuming that the power-on moment is within the positive half cycle of the AC power V _AC (the live pin L2 is positive and the neutral pin N2 is negative), the energy of the AC power V _AC will be transmitted to the rectifier 40 in sequence through the live pin L2, the capacitor CX, the resistor R1 and the diode DX1, and then turn on the diodes D1 and D4 in the rectifier 40 and turn off the diodes D2 and D3, and then return to the neutral pin N2. After the rectifier 40 converts the AC power source V _AC into the input voltage V _IN , the energy of the input voltage V _IN will charge the energy storage capacitor C1 and the excitation inductor LM. At this time, the control circuit 60 starts to work, and outputs the control signal GD1 through the pin P1 to make the power switch Q1 switch at a high frequency, so that the excitation inductor LM can store and release energy, allowing the transformer TR to sense the energy on the primary side to the secondary side to establish the output voltage V _OUT . At the same time, the voltage detection circuit 50 will transmit the detected feedback voltage V _FB to the pin P3 of the control circuit 60. When the control circuit 60 determines that the value of the feedback voltage V _FB is greater than a predetermined value, it means that the output voltage V _OUT has been established, and the load device 200 will operate in the AC mode (powered by the output voltage V _OUT ). In this case, the control circuit 60 will output the control signal GD2 with an enable potential to the path control circuit 30 through the pin P2 to turn on the auxiliary switch Q2, thereby activating the loop of the protection circuit 20. At this time, the energy of the AC power source V _AC is not only transmitted to the rectifier 40 through the live wire pin L2, capacitor CX, resistor R1 and diode DX1, but also transmitted to the rectifier 40 through the protection circuit 20, the turned-on auxiliary switch Q2 and resistor R2, that is, the protection circuit 20 starts to operate to provide over-current protection. In addition, the control circuit 60 adjusts the duty cycle of the control signal GD1 according to the feedback voltage V _FB , thereby achieving the effect of stabilizing the output voltage V _OUT . By disconnecting the loop of the protection circuit 20 at the moment of connecting to the mains, and then activating the loop of the protection circuit 20 after the output voltage V _OUT is established, the present invention can prevent the protection circuit 20 from being burned out by a huge surge current at the moment when the mains supply end, the power supply 100 and the dynamically variable load device 200 are connected.

If the power-on moment is in the negative half cycle of the AC power source V _AC (the live pin L2 is at a negative potential, and the neutral pin N2 is at a positive potential), the energy of the AC power source V _AC will turn on the diodes D2 and D3 in the rectifier 40 and turn off the diodes D1 and D4 through the neutral pin N2, and then be transferred back to the live pin L2 through the diode DX2, the resistor R1 and the capacitor CX. After the rectifier 40 converts the AC power source V _AC into the input voltage V _IN , the energy of the input voltage V _IN will charge the energy storage capacitor C1 and the excitation inductor LM. At this time, the control circuit 60 starts to work, and outputs the control signal GD1 through the pin P1 to make the power switch Q1 switch at a high frequency, so that the excitation inductor LM can store and release energy, so that the transformer TR can sense the energy on the primary side to the secondary side to establish the output voltage V _OUT . At the same time, the voltage detection circuit 50 will transmit the detected feedback voltage V _FB to the pin P3 of the control circuit 60. When the control circuit 60 determines that the value of the feedback voltage V _FB is greater than a predetermined value, it means that the output voltage V _OUT has been established, and the load device 200 will operate in the AC mode (powered by the output voltage V _OUT ). In this case, the control circuit 60 outputs a control signal GD2 with an enable potential to the path control circuit 30 through the pin P2 to turn on the auxiliary switch Q2, thereby activating the loop of the protection circuit 20. At this time, the energy of the AC power source V _AC is not only transmitted back to the live pin L2 through the diode D2, the diode D3, the diode DX2, the resistor R1 and the capacitor CX, but also transmitted back to the live pin L2 through the resistor R2, the turned-on auxiliary switch Q2 and the protection circuit 20, that is, the protection circuit 20 starts to operate to provide over-current protection. In addition, the control circuit 60 adjusts the duty cycle of the control signal GD1 according to the feedback voltage V _FB , thereby achieving the effect of stabilizing the output voltage V _OUT . By disconnecting the loop of the protection circuit 20 at the moment of connecting to the mains, and then activating the loop of the protection circuit 20 after the output voltage V _OUT is established, the present invention can prevent the protection circuit 20 from being burned out by a huge surge current at the moment when the mains supply end, the power supply 100 and the dynamically variable load device 200 are connected.

On the other hand, the control circuit 60 can obtain the voltage across the resistor R2 and the voltage polarity detection voltage Vx through the pins P4 and P5, and judge the positive and negative cycles of the AC power source V _AC and whether the protection circuit 20 is activated, and then output the corresponding logic signal VL. The following table 1 shows an example of the definition method of the logic signal VL, but does not limit the scope of the present invention. Status definition V L Logical definition Protection circuit loop disconnected N/A 00 Positive half cycle of AC voltage (protection circuit action) Positive voltage 01 Negative half cycle of AC voltage (protection circuit action) Negative voltage 10 Table I

When the embedded controller 210 of the load device 200 receives the logic signal VL through the detection pin T2 of the socket JACK1, the positive and negative cycles of the AC power source V _AC and whether the protection circuit 20 is in operation can be known according to the logic definition of the value of the logic signal VL.

In the embodiment of the present invention, the power switch Q1 and the auxiliary switch Q2 may be metal-oxide-semiconductor field-effect transistors (MOSFET), bipolar junction transistors (BJT), or other elements with similar functions. For N-type transistors, the enable potential is a high potential, and the disable potential is a low potential; for P-type transistors, the enable potential is a low potential, and the disable potential is a high potential. However, the types of the power switch Q1 and the auxiliary switch Q2 do not limit the scope of the present invention.

In summary, when the power supply is coupled to the load device but not connected to the mains, the present invention will first disconnect the loop of the protection circuit until the output voltage is established and then start the loop of the protection circuit to provide over-current protection, thereby preventing the protection circuit from being burned out by the huge surge current at the moment of power on, causing the power supply to be permanently damaged and unable to operate. Therefore, the present invention can provide a power supply that can provide over-current protection under high dynamic load changes. The above is only a preferred embodiment of the present invention, and all equal changes and modifications made according to the scope of the patent application of the present invention should be covered by the present invention.

10: Buffer circuit 20: Protection circuit 30: Path control circuit 40: Rectifier 50: Voltage detection circuit 60: Control circuit 100: Power supply 200: Load device 210: Embedded controller 220: Charging integrated circuit 230: Battery 300: Electronic system NP: Primary winding and turns NS: Secondary winding and turns GND1, GND2: Ground potential TR: Transformer Q1: Power switch Q2: Auxiliary switch C1, C2: Energy storage capacitor CX: Capacitor DO, DX1-DX2, D1-D4: Diode RD1, RD2: Divider resistor R1-R3: Resistor LM: Magnetizing inductor V _IN : Input voltage V _OUT : Output voltage V _AC :AC voltage V _FB :Feedback voltage Vx:Detection voltage V _BAT :Battery voltage I _IN :Input current I _OUT :Output current GD1, GD2:Control signal VL:Logic signal PLUG1, PLUG2:Connector JACK1, JACK2:Socket PD1, PD2:Power pin G1, G2:Ground pin T1, T2:Detection pin L1, L2:Live pin N1, N2:Neutral pin P1-P5:Pin

FIG. 1 is a functional block diagram of an electronic system in an embodiment of the present invention. FIG. 2 is a functional block diagram of an electronic system in an embodiment of the present invention. FIG. 3 is a functional block diagram of a power supply in an electronic system in an embodiment of the present invention. FIG. 4 is a schematic diagram of the implementation of a power supply in an electronic system in an embodiment of the present invention.

10: Buffer circuit

20: Protection circuit

30: Path control circuit

40: Rectifier

50: Voltage detection circuit

60: Control circuit

100: Power supply

GND1, GND2: ground potential

TR: Transformer

Q1: Power switch

C1, C2: Energy storage capacitors

DO:Diode

LM: Magnetizing inductance

V _OUT : Output voltage

V _AC : Alternating current voltage

V _FB : Feedback voltage

Vx: Detection voltage

GD1, GD2: control signal

VL:Logic signal

PD1: Power pin

G1: Ground pin

T1: Detect foot position

L2: FireWire pin

N2: Neutral pin

Claims (10)

A power supply for providing overcurrent protection under dynamic load changes, comprising: A first input terminal and a second input terminal for receiving an AC power source provided by a mains power supply terminal; A first output terminal and a second output terminal, coupled to a load device, for outputting an output voltage to drive the load device; A rectifier for converting the AC power source into an input voltage; A transformer for inducing the energy of the input voltage from a primary side to a secondary side to supply the output voltage, comprising: A primary side winding, arranged on the primary side, comprising a first tapped end and a second non-tapped end; and A secondary winding, disposed on the secondary side, comprising a second dotted end and a second non-dotted end; A first switch, comprising: A first end, coupled to the first non-dotted end of the primary winding in the transformer; A second end, coupled to a first ground potential; and A control end, for receiving a first control signal for switching between a first enable potential and a first disable potential; A buffer circuit, coupled between the first input end and the rectifier, for buffering the effect of a surge current; A protection circuit, for providing over-current protection on the primary side; A voltage detection circuit, disposed on the secondary side, for providing a feedback voltage related to the output voltage; A path control circuit is used to: cut off the loop of the protection circuit after the power supply is coupled to the mains supply terminal but before the output voltage is established; and activate the loop of the protection circuit after receiving a second control signal with a second enable potential; and a control circuit is arranged on the primary side, and is used to: provide the first control signal through a first pin, and adjust the duty cycle of the first control signal according to the value of the feedback voltage; when it is determined that the output voltage has been established according to the value of the feedback voltage, output the second control signal with the second enable potential to the path control circuit through a second pin; and receive the feedback voltage through a third pin. A power supply as described in claim 1, wherein the buffer circuit comprises: a capacitor comprising: a first end coupled to the first input end; and a second end; a first resistor comprising: a first end coupled to the second end of the capacitor; and a second end; a first diode comprising: an anode coupled to the second end of the first resistor; and a cathode coupled to the rectifier; and a second diode comprising: an anode coupled to the rectifier; and a cathode coupled to the second end of the first resistor. A power supply as described in claim 1, wherein the path control circuit comprises: a second switch comprising: a first end coupled to the protection circuit; a second end coupled to the rectifier; and a control end coupled to the second pin of the control circuit to receive the second control signal. The power supply as described in claim 3 further comprises a third output terminal for outputting a logic signal to the load device, wherein: The path control circuit further comprises a second resistor, a first end of which is coupled to the second end of the second switch and a fourth pin of the control circuit, and a second end of which is coupled to the rectifier and a fifth pin of the control circuit; and The control circuit is further used to: Calculate a corresponding detection voltage according to the voltage difference between the fourth pin and the fifth pin; and Output the logic signal according to the value of the detection voltage. A power supply as described in claim 4, wherein: The control circuit is further used to: output the logic signal with a first value when the value of the detection voltage is a positive value; output the logic signal with a second value when the value of the detection voltage is a negative value; output the logic signal with a third value when the value of the detection voltage cannot be determined; the first value corresponds to a positive half cycle of the AC power source and the circuit of the protection circuit is activated; the second value corresponds to a negative half cycle of the AC power source and the circuit of the protection circuit is activated; and the third value corresponds to the circuit of the protection circuit being disconnected. A power supply as described in claim 3, wherein the path control circuit further comprises: A third resistor comprising: A first end coupled to the control end of the second switch; and A second end coupled to the second pin of the control circuit. A power supply as described in claim 1, wherein the voltage detection circuit comprises: a first voltage-dividing resistor, comprising: a first end coupled to the first output end; and a second end coupled to the third pin of the control circuit; and a second voltage-dividing resistor, comprising: a first end coupled to the second end of the first voltage-dividing resistor; and a second end coupled to a second ground potential. The power supply as described in claim 1 further comprises: a magnetizing inductor, a first end of which is coupled to the first dotted end of the primary side winding, and a second end of which is coupled to the first non-dotted end of the primary side winding; and a first energy storage capacitor, comprising: a first end coupled to the first dotted end of the primary side winding; and a second end coupled to the first ground potential. The power supply as described in claim 1 further comprises: an output diode comprising: an anode coupled to the second non-pointing end of the secondary winding; and a cathode coupled to the first output end; and a second energy storage capacitor comprising: a first end coupled to the first output end; and a second end coupled to a second ground potential and the second output end. A power supply as described in claim 1, wherein the protection circuit includes a fuse for performing self-melting to cut off the input current when the value of an input current flowing through the primary side is greater than a predetermined value.

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