Power supply circuit and switching power supply

Abstract

The utility model discloses a power supply circuit and a switching power supply, and relates to the technical field of switching power supplies. The power supply circuit comprises a PFC power supply circuit, an LLC power supply circuit and a delay switch circuit. The PFC power supply circuit outputs a power supply to supply power to the PFC chip, the PFC chip is started, the output voltage Vbulk is gradually increased, when the Vbulk voltage is smaller than a preset required voltage, the delay switch circuit controls the circuit between the PFC power supply circuit and the LLC power supply circuit to be disconnected, and at the moment, no power supply is input to the LLC chip. When the Vbulk voltage is larger than or equal to the preset required voltage, the delay switch circuit controls the circuit between the PFC power supply circuit and the LLC power supply circuit to be switched on, at the moment, the LLC power supply circuit outputs a power supply to the LLC chip, and the LLC chip is started. Therefore, starting of the LLC chip is delayed, and circuit element damage caused by overlarge instantaneous current is avoided.

Description

Technical Field

[0001] This utility model relates to the field of switching power supply technology, and in particular to a power supply circuit and a switching power supply. Background Technology

[0002] In switching power supplies, the coordinated operation of the Power Factor Correction (PFC) circuit and the LLC resonant circuit is crucial for ensuring stable power output. The PFC circuit corrects the power factor of the input power supply before outputting the power to the LLC resonant circuit. The LLC resonant circuit then performs voltage transformation and other processing on the received power supply before outputting it to the load.

[0003] However, the output voltage Vbulk of the PFC circuit has a certain rise delay during startup, causing it to fail to reach the power supply requirement in time at startup. If the LLC circuit still attempts to drive the output at this point, the control logic of the LLC resonant circuit may incorrectly increase the drive signal because the set Vbulk has not been reached, resulting in a sharp increase in instantaneous current. This peak current can place an excessive current load on critical components such as MOSFETs, potentially causing them to overheat or be damaged. Utility Model Content

[0004] The main purpose of this utility model is to provide a power supply circuit that solves the problem that the LLC circuit of the existing switching power supply incorrectly increases the drive signal when the set Vbulk is not reached, resulting in excessive instantaneous current and damage to circuit components.

[0005] To achieve the above objectives, the power supply circuit proposed in this utility model is applied to a switching power supply, which includes a PFC chip and an LLC chip. The power supply circuit includes:

[0006] The PFC power supply circuit has its power output terminal connected to the power supply terminal of the PFC chip, and the PFC power supply circuit is used to output power supply.

[0007] LLC power supply circuit, wherein the power output terminal of the LLC power supply circuit is connected to the power supply terminal of the LLC chip;

[0008] A delay switch circuit is provided, wherein the controlled terminal of the delay switch circuit is connected to the output terminal of the PFC chip, the first terminal of the delay switch circuit is connected to the power output terminal of the PFC power supply circuit, and the second terminal of the delay switch circuit is connected to the power input terminal of the LLC power supply circuit.

[0009] The delay switch circuit is used to control the conduction state of the circuit between the power output terminal of the PFC power circuit and the power input terminal of the LLC power circuit according to the voltage magnitude of the output voltage of the PFC chip.

[0010] In one embodiment, the delay switching circuit includes:

[0011] A detection circuit is connected to the output terminal of the PFC chip. The detection circuit is used to detect the output voltage of the PFC chip and output a corresponding control signal.

[0012] A switching circuit is provided, wherein the signal input terminal of the switching circuit is connected to the signal output terminal of the detection circuit, the first terminal of the switching circuit is connected to the power output terminal of the PFC power supply circuit, and the second terminal of the switching circuit is connected to the power input terminal of the LLC power supply circuit. The switching circuit is used to control the conduction state of the circuit between the power output terminal of the PFC power supply circuit and the power input terminal of the LLC power supply circuit according to the control signal.

[0013] In one embodiment, the detection circuit includes a voltage regulator, the adjustment terminal of which is connected to the output terminal of the PFC chip, the first terminal of which is grounded, and the second terminal of which is connected to the signal input terminal of the switching circuit.

[0014] In one embodiment, the switching circuit includes a first switching transistor, a second switching transistor, a first resistor, and a second resistor; the controlled terminal of the first switching transistor and one end of the first resistor are connected to the signal output terminal of the detection circuit; the other end of the first resistor and the first end of the first switching transistor are connected to the power input terminal of the switching circuit; the second end of the first switching transistor is connected to one end of the second resistor; the other end of the second resistor is connected to the controlled terminal of the second switching transistor; the first end of the second switching transistor is connected to the power output terminal of the PFC power supply circuit, and the second end of the second switching transistor is connected to the power input terminal of the LLC power supply circuit.

[0015] In one embodiment, the PFC power supply circuit includes a first transformer, a first diode, a first capacitor, and a second capacitor; a first end of the auxiliary winding of the first transformer is connected to the positive terminal of the first diode; the negative terminal of the first diode, one end of the first capacitor, and the positive terminal of the second capacitor are connected to the power output terminal of the PFC power supply circuit; a second end of the auxiliary winding of the first transformer, the other end of the first capacitor, and the negative terminal of the second capacitor are grounded.

[0016] In one embodiment, the LLC power supply circuit includes a second diode, the anode of which is connected to the power input terminal of the LLC power supply circuit, and the cathode of which is connected to the LLC chip.

[0017] In one embodiment, the detection circuit further includes a third resistor, a fourth resistor, a fifth resistor, a sixth resistor, and a third capacitor;

[0018] Wherein, one end of the third resistor is connected to the output terminal of the PFC chip, the other end of the third resistor is connected to one end of the fourth resistor, the other end of the fourth resistor is connected to one end of the fifth resistor, the other end of the fifth resistor, one end of the sixth resistor, and one end of the third capacitor are connected to the adjustment terminal of the voltage regulator; the other end of the sixth resistor and the other end of the third capacitor are grounded.

[0019] In one embodiment, the first switching transistor is a PNP transistor, the base of the PNP transistor is the controlled terminal of the first switching transistor, the emitter of the PNP transistor is the first terminal of the first switching transistor, the collector of the PNP transistor is the second terminal of the first switching transistor, and / or,

[0020] The second switching transistor is an NPN transistor, the base of which is the controlled terminal of the second switching transistor, the collector of which is the first terminal of the second switching transistor, and the emitter of which is the second terminal of the second switching transistor.

[0021] In one embodiment, the switching circuit further includes a seventh resistor and an eighth resistor. One end of the seventh resistor is connected to the signal output terminal of the detection circuit, and the other end of the seventh resistor, the controlled terminal of the first switching transistor, and one end of the first resistor are connected. One end of the eighth resistor is connected to the power input terminal of the switching circuit, and the other end of the eighth resistor is connected to the first terminal of the first switching transistor.

[0022] This utility model also proposes a switching power supply, including the power supply circuit described above.

[0023] This utility model employs a power supply circuit applied to a switching power supply. The switching power supply includes a PFC chip and an LLC chip. The power supply circuit comprises a PFC power supply circuit, an LLC power supply circuit, and a delay switch circuit. The PFC power supply circuit outputs power to the PFC chip first. After the PFC chip starts up, its output voltage Vbulk gradually increases. When the output voltage Vbulk is lower than a preset voltage, the delay switch circuit disconnects the circuit between the power output terminal of the PFC power supply circuit and the power input terminal of the LLC power supply circuit, at which point the LLC chip receives no power. When the output voltage Vbulk is greater than or equal to the preset required voltage, the delay switch circuit connects the circuit between the power output terminal of the PFC power supply circuit and the power input terminal of the LLC power supply circuit, allowing the LLC power supply circuit to output power to the LLC chip, and the LLC chip begins to start up. Thus, this utility model delays the start-up of the LLC chip, ensuring that the PFC chip's output voltage Vbulk has reached the preset required voltage by the time the LLC chip starts up. In this way, the present invention will not erroneously increase the duty cycle of the drive signal, and will not cause damage to key components such as MOSFETs. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of this utility model or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this utility model. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0025] Figure 1 A schematic diagram of an embodiment of the power supply circuit provided by this utility model;

[0026] Figure 2 Electronic circuit diagram of another embodiment of the power supply circuit provided by this utility model;

[0027] Figure 3 An electronic circuit diagram of an exemplary power supply circuit provided for this utility model.

[0028] Explanation of icon numbers:

[0029]

[0030] The realization of the purpose, functional features and advantages of this utility model will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0031] The technical solutions of the present utility model will be clearly and completely described below with reference to the accompanying drawings of the embodiments. Obviously, the described embodiments are only some embodiments of the present utility model, and not all embodiments. Based on the embodiments of the present utility model, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the protection scope of the present utility model.

[0032] It should be noted that all directional indicators (such as up, down, left, right, front, back, etc.) in this utility model embodiment are only used to explain the relative positional relationship and movement of each component in a certain specific posture (as shown in the figure). If the specific posture changes, the directional indicator will also change accordingly.

[0033] Furthermore, the use of terms such as "first" and "second" in this utility model is for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. Additionally, the technical solutions of the various embodiments can be combined with each other, but only on the basis of being achievable by those skilled in the art. When the combination of technical solutions is contradictory or impossible to implement, such a combination of technical solutions should be considered non-existent and not within the scope of protection claimed by this utility model.

[0034] In existing switching power supplies, the PFC circuit is responsible for power factor correction of the input power supply, and then outputs the power supply to the LLC resonant circuit. The LLC resonant circuit performs voltage transformation and other processing on the received power supply before outputting it to the load.

[0035] Please see Figure 3In an exemplary power supply circuit, the PFC circuit includes a PFC chip, and the LLC resonant circuit includes an LLC chip. This exemplary power supply circuit supplies power to the PFC chip and the LLC chip via VCC3 and VCC4 terminals, respectively. In this exemplary power supply circuit, the auxiliary winding of the second transformer T2 receives power; one path supplies power to the PFC chip via the third diode D3, the fourth capacitor C4, the fifth capacitor C5, and the VCC3 terminal; the other path supplies power to the LLC chip via the fourth diode D4, the sixth capacitor C6, the seventh capacitor C7, and the VCC4 terminal. In this exemplary power supply circuit, the power supply to the PFC chip and the LLC chip is simultaneously turned on and off. However, the PFC chip has a delay in output startup. The output voltage Vbulk of the PFC chip will rise for a period of time before stabilizing after reaching the preset required voltage. If the PFC chip and LLC chip are powered at the same time, the output voltage Vbulk of the PFC chip will not reach the preset required voltage at the moment of startup. The LLC chip will output the drive incorrectly, the duty cycle of the output drive signal will increase, and the instantaneous current will increase, which will lead to the damage of key components such as MOSFETs.

[0036] This utility model proposes a power supply circuit.

[0037] Please see Figure 1 In one embodiment of this utility model, the power supply circuit is applied to a switching power supply, which includes a PFC chip and an LLC chip. The power supply circuit includes:

[0038] PFC power supply circuit 20, the power output terminal of PFC power supply circuit 20 is connected to the power supply terminal of PFC chip, PFC power supply circuit 20 is used to output power supply.

[0039] It should be noted that the PFC power supply circuit 20 may include a power input circuit and a rectifier and filter circuit. The power input circuit receives the power supply, which is then rectified and filtered before being output. The transformer in the switching power supply may include a main winding, a secondary winding, and an auxiliary winding. When the high-frequency switch is turned on, the current in the main winding establishes a magnetic field in the transformer core, storing energy. When the switch is turned off, the energy stored in the magnetic field is released through the secondary winding to supply the load. The auxiliary winding can utilize the magnetic flux generated by the main winding to generate an induced voltage to power the control system. In this embodiment, the power input circuit may include a transformer, from which the power supply is induced and output from the auxiliary winding. The rectifier and filter circuit may include diodes, capacitors, and other components to rectify and filter the power supply before output. In this embodiment, the PFC power supply circuit 20 can output power to power the PFC chip.

[0040] LLC power supply circuit 30, the power output terminal of LLC power supply circuit 30 is connected to the power supply terminal of LLC chip. In this embodiment, LLC power supply circuit 30 can output power to supply power to LLC chip.

[0041] The delay switch circuit 10 has a controlled terminal connected to the output terminal of the PFC chip, a first terminal connected to the power output terminal of the PFC power supply circuit 20, and a second terminal connected to the power input terminal of the LLC power supply circuit 30.

[0042] The delay switch circuit 10 is used to control the conduction state of the circuit between the power output terminal of the PFC power supply circuit 20 and the power input terminal of the LLC power supply circuit 30 according to the voltage magnitude of the output voltage of the PFC chip.

[0043] In this embodiment, the PFC power supply circuit 20 outputs power to the PFC chip first. After the PFC chip starts up, its output voltage Vbulk gradually increases. When the output voltage Vbulk is less than a preset voltage, the delay switch circuit 10 disconnects the circuit between the power output terminal of the PFC power supply circuit 20 and the power input terminal of the LLC power supply circuit 30, at which point the LLC chip receives no power. When the output voltage Vbulk is greater than or equal to the preset required voltage, the delay switch circuit 10 connects the circuit between the power output terminal of the PFC power supply circuit 20 and the power input terminal of the LLC power supply circuit 30, allowing the LLC power supply circuit 30 to output power to the LLC chip, and the LLC chip starts up. Thus, this embodiment delays the start-up of the LLC chip, ensuring that the PFC chip's output voltage Vbulk has reached the preset required voltage by the time the LLC chip starts up. Therefore, compared to the exemplary power supply circuit, this embodiment does not erroneously increase the duty cycle of the drive signal, thus preventing damage to critical components such as the MOSFET.

[0044] In this invention, the PFC power supply circuit 20 outputs power to the PFC chip first. After the PFC chip starts up, its output voltage Vbulk gradually increases. When the output voltage Vbulk is less than a preset voltage, the delay switch circuit 10 disconnects the circuit between the power output terminal of the PFC power supply circuit 20 and the power input terminal of the LLC power supply circuit 30, at which point the LLC chip receives no power. When the output voltage Vbulk is greater than or equal to the preset required voltage, the delay switch circuit 10 connects the circuit between the power output terminal of the PFC power supply circuit 20 and the power input terminal of the LLC power supply circuit 30, allowing the LLC power supply circuit 30 to output power to the LLC chip, and the LLC chip starts up. Thus, this invention delays the start-up of the LLC chip, ensuring that the PFC chip's output voltage Vbulk has reached the preset required voltage by the time the LLC chip starts up. This prevents the incorrect increase of the drive signal's duty cycle and avoids damage to critical components such as the MOSFET.

[0045] Please see Figure 2 In one embodiment of this utility model, the delay switch circuit 10 includes:

[0046] The detection circuit 11 is connected to the output terminal of the PFC chip. The detection circuit 11 is used to detect the output voltage of the PFC chip and output the corresponding control signal.

[0047] The switching circuit 12 has its signal input terminal connected to the signal output terminal of the detection circuit 11. The first terminal of the switching circuit 12 is connected to the power output terminal of the PFC power circuit 20, and the second terminal of the switching circuit 12 is connected to the power input terminal of the LLC power circuit 30. The switching circuit 12 is used to control the conduction state of the circuit between the power output terminal of the PFC power circuit 20 and the power input terminal of the LLC power circuit 30 according to the control signal.

[0048] In this embodiment, the detection circuit 11 can detect the output voltage of the PFC chip and output a corresponding control signal. For example, it outputs a high level when the output voltage of the PFC chip has not reached the preset required voltage, and outputs a low level when the output voltage of the PFC chip reaches the preset required voltage. The switching circuit 12 can disconnect the circuit between the power output terminal of the PFC power circuit 20 and the power input terminal of the LLC power circuit 30 when the control signal is high; and connect the circuit between the power output terminal of the PFC power circuit 20 and the power input terminal of the LLC power circuit 30 when the control signal is low. Thus, this embodiment can delay the startup of the LLC chip, so that when the LLC chip starts up, the output voltage Vbulk of the PFC chip has already reached the preset required voltage.

[0049] Please see Figure 2 In one embodiment of the present invention, the detection circuit 11 includes a voltage regulator U1. The adjustment terminal of the voltage regulator U1 is connected to the output terminal of the PFC chip. The first terminal of the voltage regulator U1 is grounded, and the second terminal of the voltage regulator U1 is connected to the signal input terminal of the switching circuit 12.

[0050] In this embodiment, when the output voltage of the PFC chip does not reach the preset required voltage, the voltage regulator U1 can be in the off state; when the output voltage of the PFC chip reaches the preset required voltage, the voltage regulator U1 can be in the on state. Therefore, in this embodiment, the voltage regulator U1 can change its own operating state according to the output voltage of the PFC chip to output corresponding control signals.

[0051] In one feasible embodiment, the voltage regulator U1 can be a BR431M chip. The anode of the BR431M chip is grounded, the cathode is connected to the signal input terminal of the switching circuit 12, and the adjustment terminal is connected to the output terminal of the PFC chip. The BR431M chip has the advantages of maintaining good stability and high accuracy under different temperatures.

[0052] In another feasible embodiment, the detection circuit 11 further includes a third resistor R3, a fourth resistor R4, a fifth resistor R5, a sixth resistor R6, and a third capacitor C3.

[0053] Among them, one end of the third resistor R3 is connected to the output terminal of the PFC chip, the other end of the third resistor R3 is connected to one end of the fourth resistor R4, the other end of the fourth resistor R4 is connected to one end of the fifth resistor R5, the other end of the fifth resistor R5, one end of the sixth resistor R6, and one end of the third capacitor C3 are connected to the adjustment terminal of the voltage regulator U1; the other end of the sixth resistor R6 and the other end of the third capacitor C3 are grounded.

[0054] In this embodiment, the voltage divider network formed by the third resistor R3, the fourth resistor R4, and the fifth resistor R5 can reduce the output voltage Vbulk of the PFC chip to a safer and detectable level. The filter network formed by the sixth resistor R6 and the third capacitor C3 can smooth out voltage fluctuations caused by the output voltage Vbulk, protecting the safe use of the voltage regulator U1 and improving detection stability.

[0055] Please see Figure 2In one embodiment of this utility model, the switching circuit 12 includes a first switching transistor Q1, a second switching transistor Q2, a first resistor R1, and a second resistor R2; the controlled terminal of the first switching transistor Q1 and one end of the first resistor R1 are connected to the signal output terminal of the detection circuit 11; the other end of the first resistor R1 and the first end of the first switching transistor Q1 are connected to the power input terminal of the switching circuit 12; the second end of the first switching transistor Q1 is connected to one end of the second resistor R2; the other end of the second resistor R2 is connected to the controlled terminal of the second switching transistor Q2; the first end of the second switching transistor Q2 is connected to the power output terminal of the PFC power supply circuit 20, and the second end of the second switching transistor Q2 is connected to the power input terminal of the LLC power supply circuit 30.

[0056] In this embodiment, the conduction state of the circuit between the power output terminal of the PFC power circuit 20 and the power input terminal of the LLC power circuit 30 is controlled by two-stage switching transistors, resulting in more stable control.

[0057] In one feasible embodiment, the first switching transistor Q1 is a PNP transistor, the base of the PNP transistor is the controlled terminal of the first switching transistor Q1, the emitter of the PNP transistor is the first terminal of the first switching transistor Q1, and the collector of the PNP transistor is the second terminal of the first switching transistor Q1.

[0058] And / or, the second switch Q2 is an NPN transistor, the base of the NPN transistor is the controlled terminal of the second switch Q2, the collector of the NPN transistor is the first terminal of the second switch Q2, and the emitter of the NPN transistor is the second terminal of the second switch Q2.

[0059] In this embodiment, the first switching transistor Q1 can be a PNP transistor and the second switching transistor Q2 can be an NPN transistor. The two can work together effectively to accurately control the conduction state of the circuit between the power output terminal of the PFC power supply circuit 20 and the power input terminal of the LLC power supply circuit 30.

[0060] In another feasible embodiment, the switching circuit 12 further includes a seventh resistor R7 and an eighth resistor R8. One end of the seventh resistor R7 is connected to the signal output terminal of the detection circuit 11, and the other end of the seventh resistor R7, the controlled terminal of the first switching transistor Q1, and one end of the first resistor R1 are connected. One end of the eighth resistor R8 is connected to the power input terminal of the switching circuit 12, and the other end of the eighth resistor R8 is connected to the first terminal of the first switching transistor Q1.

[0061] In this embodiment, the seventh resistor R7 and the eighth resistor R8 can be used for current limiting to protect the circuit.

[0062] Please see Figure 2In one embodiment of this utility model, the PFC power supply circuit 20 includes a first transformer T1, a first diode D1, a first capacitor C1, and a second capacitor C2; the first end of the auxiliary winding of the first transformer T1 is connected to the positive terminal of the first diode D1; the negative terminal of the first diode D1, one end of the first capacitor C1, and the positive terminal of the second capacitor C2 are connected to the power output terminal of the PFC power supply circuit 20; the second end of the auxiliary winding of the first transformer T1, the other end of the first capacitor C1, and the negative terminal of the second capacitor C2 are grounded.

[0063] In this embodiment, the second capacitor C2 can specifically be an electrolytic capacitor. The auxiliary winding of the first transformer T1 outputs a power supply, which is rectified by the first diode D1 and filtered by the first capacitor C1 and the second capacitor C2 before being output.

[0064] Please see Figure 2 In one embodiment of the present invention, the LLC power supply circuit 30 includes a second diode D2, the positive terminal of the second diode D2 is connected to the power input terminal of the LLC power supply circuit 30, and the negative terminal of the second diode D2 is connected to the LLC chip.

[0065] In this embodiment, the second diode D2 can prevent the impact of reverse current and improve the circuit's anti-interference capability.

[0066] To help understand the circuit principle of this invention, please refer to [link / reference needed]. Figure 2 In one embodiment of this utility model, the auxiliary winding of transformer T1 can output power, which is rectified and filtered by a circuit consisting of a first diode D1, a first capacitor C1, and a second capacitor C2, and then output to the PFC chip via VCC1. The PFC chip starts working, and the output voltage Vbulk increases. Assuming that voltage regulator U1 is turned on when the voltage is greater than or equal to 2.5V and turned off when the voltage is less than 2.5V, the corresponding preset required voltage is:

[0067] Vbulk1=(1+(R3+R4+R5) / R6)×2.5V

[0068] Assuming that the resistance values ​​of R3, R4 and R5 are all 330kΩ and the resistance value of R6 is 7.5kΩ, the preset required voltage Vbulk1 can be calculated to be 332.5V, which is close to 330V.

[0069] When the output voltage Vbulk of the PFC is less than Vbulk1, the voltage regulator U1 is in the off state. At this time, the base of the PNP transistor is at a high level and the collector is at a low level. At this time, the base of the NPN transistor is at a low level and is in the off state. There is no power supply output at the VCC2 terminal.

[0070] When the output voltage Vbulk of the PFC is greater than or equal to Vbulk1, the voltage regulator U1 is in the open state. At this time, the base of the PNP transistor is at a low level and the collector is at a high level. At this time, the base of the NPN transistor is at a high level and is in the conducting state. There is no power supply output at the VCC2 terminal.

[0071] Thus, this embodiment delays the startup of the LLC chip, so that when the LLC chip starts up, the output voltage Vbulk of the PFC chip has already reached the preset required voltage. This can reduce the inrush current of the MOSFET, avoid component damage, and allow the use of a MOSFET with a smaller current, thereby reducing component costs.

[0072] This utility model also proposes a switching power supply, which includes a power supply circuit. The specific structure of the power supply circuit is as described in the above embodiments. Since this switching power supply adopts all the technical solutions of all the above embodiments, it has at least all the beneficial effects brought about by the technical solutions of the above embodiments, which will not be described in detail here.

[0073] The above description is merely an exemplary embodiment of the present utility model and does not limit the patent scope of the present utility model. Any equivalent structural transformations made based on the technical concept of the present utility model and the contents of the present utility model specification and drawings, or direct / indirect applications in other related technical fields, are included within the patent protection scope of the present utility model.

Claims

1. A power supply circuit applied to a switching power supply, the switching power supply comprising a PFC chip and an LLC chip, characterized in that, The power supply circuit includes: The PFC power supply circuit has its power output terminal connected to the power terminal of the PFC chip, and the PFC power supply circuit is used to output power supply. LLC power supply circuit, wherein the power output terminal of the LLC power supply circuit is connected to the power supply terminal of the LLC chip; A delay switch circuit is provided, wherein the controlled terminal of the delay switch circuit is connected to the output terminal of the PFC chip, the first terminal of the delay switch circuit is connected to the power output terminal of the PFC power supply circuit, and the second terminal of the delay switch circuit is connected to the power input terminal of the LLC power supply circuit. The delay switch circuit is used to control the conduction state of the circuit between the power output terminal of the PFC power circuit and the power input terminal of the LLC power circuit according to the voltage magnitude of the output voltage of the PFC chip.

2. The power supply circuit as described in claim 1, characterized in that, The time-delay switching circuit includes: A detection circuit is connected to the output terminal of the PFC chip. The detection circuit is used to detect the output voltage of the PFC chip and output a corresponding control signal. A switching circuit is provided, wherein the signal input terminal of the switching circuit is connected to the signal output terminal of the detection circuit, the first terminal of the switching circuit is connected to the power output terminal of the PFC power supply circuit, and the second terminal of the switching circuit is connected to the power input terminal of the LLC power supply circuit. The switching circuit is used to control the conduction state of the circuit between the power output terminal of the PFC power supply circuit and the power input terminal of the LLC power supply circuit according to the control signal.

3. The power supply circuit as described in claim 2, characterized in that, The detection circuit includes a voltage regulator, the adjustment terminal of which is connected to the output terminal of the PFC chip, the first terminal of which is grounded, and the second terminal of which is connected to the signal input terminal of the switching circuit.

4. The power supply circuit as described in claim 2, characterized in that, The switching circuit includes a first switching transistor, a second switching transistor, a first resistor, and a second resistor; the controlled terminal of the first switching transistor and one end of the first resistor are connected to the signal output terminal of the detection circuit; the other end of the first resistor and the first end of the first switching transistor are connected to the power input terminal of the switching circuit; the second end of the first switching transistor is connected to one end of the second resistor; the other end of the second resistor is connected to the controlled terminal of the second switching transistor; the first end of the second switching transistor is connected to the power output terminal of the PFC power supply circuit, and the second end of the second switching transistor is connected to the power input terminal of the LLC power supply circuit.

5. The power supply circuit as described in claim 1, characterized in that, The PFC power supply circuit includes a first transformer, a first diode, a first capacitor, and a second capacitor; the first end of the auxiliary winding of the first transformer is connected to the positive terminal of the first diode; the negative terminal of the first diode, one end of the first capacitor, and the positive terminal of the second capacitor are connected to the power output terminal of the PFC power supply circuit; the second end of the auxiliary winding of the first transformer, the other end of the first capacitor, and the negative terminal of the second capacitor are grounded.

6. The power supply circuit as described in claim 1, characterized in that, The LLC power supply circuit includes a second diode, the anode of which is connected to the power input terminal of the LLC power supply circuit, and the cathode of which is connected to the LLC chip.

7. The power supply circuit as described in claim 3, characterized in that, The detection circuit also includes a third resistor, a fourth resistor, a fifth resistor, a sixth resistor, and a third capacitor; Wherein, one end of the third resistor is connected to the output terminal of the PFC chip, the other end of the third resistor is connected to one end of the fourth resistor, the other end of the fourth resistor is connected to one end of the fifth resistor, the other end of the fifth resistor, one end of the sixth resistor, and one end of the third capacitor are connected to the adjustment terminal of the voltage regulator; the other end of the sixth resistor and the other end of the third capacitor are grounded.

8. The power supply circuit as described in claim 4, characterized in that, The first switching transistor is a PNP transistor, the base of the PNP transistor is the controlled terminal of the first switching transistor, the emitter of the PNP transistor is the first terminal of the first switching transistor, the collector of the PNP transistor is the second terminal of the first switching transistor, and / or, The second switching transistor is an NPN transistor, the base of which is the controlled terminal of the second switching transistor, the collector of which is the first terminal of the second switching transistor, and the emitter of which is the second terminal of the second switching transistor.

9. The power supply circuit as described in claim 4, characterized in that, The switching circuit further includes a seventh resistor and an eighth resistor. One end of the seventh resistor is connected to the signal output terminal of the detection circuit, and the other end of the seventh resistor, the controlled terminal of the first switching transistor, and one end of the first resistor are connected. One end of the eighth resistor is connected to the power input terminal of the switching circuit, and the other end of the eighth resistor is connected to the first terminal of the first switching transistor.

10. A switching power supply, characterized in that, Includes the power supply circuit as described in any one of claims 1 to 9.

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