Power control circuit for switching power supply and switching power supply

Abstract

The application provides a power control circuit of a switching power supply and the switching power supply. The power control circuit comprises a transformer, a primary winding of the transformer being connected to an input circuit and a switching unit, a control end of the switching unit being connected to a controller; a voltage detection circuit, the voltage detection circuit comprising a first optocoupler, the first optocoupler being turned on when an input voltage of the input circuit is greater than or equal to a preset voltage, and the first optocoupler being turned off when the input voltage is less than the preset voltage; a reference voltage circuit, the reference voltage circuit outputting a first reference voltage when the first optocoupler is turned on, and the reference voltage circuit outputting a second reference voltage when the first optocoupler is turned off; and a current detection circuit, the current detection circuit outputting a first feedback signal based on a load current and the first reference voltage, or outputting a second feedback signal based on the load current and the second reference voltage. The power control circuit of the application can reduce the heat of the switching power supply under low-voltage input, and no additional temperature treatment measures need to be taken for the low-voltage input.

Description

Technical Field

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

[0002] In related technologies, switching power supplies such as chargers and adapters have a wide input voltage range (AC 100V~AC240V). When the input voltage is within this wide range, the switching power supply can operate normally and meet various electrical performance requirements, safety requirements, temperature requirements, etc.

[0003] Because the current is greater at low voltage inputs than at high voltage inputs (e.g., the current is greater at AC 100V inputs than at AC 240V inputs), the corresponding losses are also greater and the temperature is higher. Therefore, in order to ensure that the switching power supply meets temperature requirements at low voltage inputs, more temperature control measures are needed, leading to increased costs. Utility Model Content

[0004] This application provides a power control circuit and a switching power supply, which can limit different output power for low-voltage input and high-voltage input of the switching power supply respectively. The maximum output power of the switching power supply is less when the input is low-voltage than when the input is high-voltage, which reduces the heat generation of the switching power supply when the input is low-voltage. Therefore, no additional temperature treatment measures are needed for the low-voltage input case, thereby reducing costs.

[0005] This application provides a power control circuit for a switching power supply, including: A transformer includes a primary winding and a secondary winding coupled to each other. The primary winding is connected to an input circuit and a switching unit. The control terminal of the switching unit is connected to a controller. The secondary winding is connected to an output circuit. A voltage detection circuit is connected to the input circuit. The voltage detection circuit includes a first optocoupler. The first optocoupler is turned on when the input voltage of the input circuit is greater than or equal to a preset voltage, and the first optocoupler is turned off when the input voltage is less than the preset voltage. A reference voltage circuit is connected to the first optocoupler. When the first optocoupler is turned on, the reference voltage circuit outputs a first reference voltage. When the first optocoupler is turned off, the reference voltage circuit outputs a second reference voltage. The first reference voltage is greater than the second reference voltage. A current detection circuit is provided, wherein the input side of the current detection circuit is connected to the output circuit and the reference voltage circuit, and the output side of the current detection circuit is connected to the controller. The current detection circuit outputs a first feedback signal based on the load current of the output circuit and the first reference voltage, or outputs a second feedback signal based on the load current of the output circuit and the second reference voltage. The first feedback signal or the second feedback signal is used to enable the controller to adjust the drive signal of the switching unit to limit the input power of the primary winding.

[0006] In some embodiments, the voltage detection circuit includes: The first voltage divider circuit is connected to the input circuit and grounded; The first Zener diode has its reference electrode connected to the first voltage divider circuit, its anode grounded, its cathode connected to the second input side of the first optocoupler, and its first input side connected to a power supply.

[0007] In some embodiments, the voltage detection circuit further includes a step-down circuit, which includes a first diode and a second Zener diode. The anode of the first diode is connected to the first voltage divider circuit, the cathode of the first diode is connected to the cathode of the second Zener diode, and the anode of the second Zener diode is connected to the reference electrode of the first Zener diode.

[0008] In some embodiments, the first voltage divider circuit includes a first resistor, a second resistor, and a third resistor connected in series. The first resistor is connected to the input circuit, the third resistor is grounded, and the reference terminal of the first Zener diode is connected between the second resistor and the third resistor.

[0009] In some embodiments, the reference voltage circuit includes: The third Zener diode has its anode grounded and its cathode connected to the power supply. The second voltage divider circuit includes a fourth resistor, a fifth resistor, and a sixth resistor. The first terminal of the fourth resistor is connected to the first terminal of the sixth resistor and connected to a power supply. The second terminal of the sixth resistor is connected to the second output side of the first optocoupler. The reference terminal of the third Zener diode, the second terminal of the fourth resistor, the first terminal of the fifth resistor, and the first output side of the first optocoupler are connected to a common node. The common node is used to output the first reference voltage or the second reference voltage. The second terminal of the fifth resistor is grounded.

[0010] In some embodiments, the current detection circuit includes: A sampling resistor is connected in series in the output circuit, and the sampling resistor obtains the sampling voltage based on the load current. The comparator has a first input terminal connected to the reference voltage circuit for inputting the first reference voltage or the second reference voltage, a second input terminal connected to the sampling resistor for inputting the sampling voltage, and an output terminal for outputting the first feedback signal or the second feedback signal.

[0011] In some embodiments, the current detection circuit further includes a second optocoupler, the first input side of the second optocoupler is connected to a power supply, the second input side of the second optocoupler is connected to the output terminal of the comparator, the first output side of the second optocoupler is grounded, and the second output side of the second optocoupler is connected to the controller.

[0012] In some embodiments, the current detection circuit further includes a second diode, the anode of which is connected to the second input side of the second optocoupler, and the cathode of which is connected to the output terminal of the comparator.

[0013] In some embodiments, the first input terminal of the comparator is a non-inverting input terminal, and the second input terminal of the comparator is an inverting input terminal; When the first reference voltage is greater than the sampling voltage, the comparator outputs a low level as the first feedback signal; When the second reference voltage is greater than the sampling voltage, the comparator outputs a low level as the second feedback signal.

[0014] This application also provides a switching power supply, including the power control circuit of any of the above embodiments.

[0015] The power control circuit of this application embodiment can limit different output power for the low-voltage input and high-voltage input of the switching power supply. The maximum output power of the switching power supply is less when the input is low-voltage than when the input is high-voltage. This can reduce the heat generation of the switching power supply when the input is low-voltage. Therefore, no additional temperature treatment measures are needed for the low-voltage input case, thereby reducing costs. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is a schematic diagram of the power control circuit according to an embodiment of this application.

[0018] Figure 2This is a circuit example diagram of a power control circuit according to an embodiment of this application. Detailed Implementation

[0019] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0020] This application provides a power control circuit for a switching power supply, which can be applied to switching power supplies such as chargers and adapters. The power control circuit can limit different output power for the low-voltage input and high-voltage input of the switching power supply, so that the maximum output power of the switching power supply under low-voltage input is less than the maximum output power of the switching power supply under high-voltage input.

[0021] refer to Figure 1 , Figure 1 This is a schematic diagram of a power control circuit 100 according to an embodiment of this application. The power control circuit 100 includes a transformer T, an input circuit 10, an output circuit 20, a switching unit 30, a controller 40, a voltage detection circuit 50, a reference voltage circuit 60, and a current detection circuit 70.

[0022] The transformer T includes a primary winding NP and a secondary winding NS that are coupled together. The primary winding NP is connected to the input circuit 10 and the switching unit 30, and the secondary winding NS is connected to the output circuit 20. The input circuit 10 is used to input voltage, which can be, for example, AC 100V to AC 240V. The output circuit 20 is used to output voltage, which can be, for example, DC voltage. In one example, the output voltage of the output circuit 20 is 20V DC voltage.

[0023] Switching unit 30 is used to control the input power or non-input power of the primary winding NP. Specifically, when switching unit 30 is turned on, the primary winding NP receives input power; when switching unit 30 is turned off, the primary winding NP receives no input power. Therefore, the magnitude of the input power of the primary winding NP can be controlled by switching unit 30, thereby controlling the magnitude of the output power of the secondary winding NS. Switching unit 30 has a control terminal, which is connected to controller 40. Controller 40 is used to drive switching unit 30 to turn on or off. In one example, controller 40 can be a PWM controller, used to output a PWM drive signal, which is used to drive switching unit 30 to turn on or off.

[0024] A voltage detection circuit 50 is connected to the input circuit 10. The voltage detection circuit 50 is used to detect the magnitude of the input voltage of the input circuit 10. The voltage detection circuit 50 includes a first optocoupler. The first optocoupler is turned on when the input voltage of the input circuit 10 is greater than or equal to a preset voltage, and turned off when the input voltage is less than the preset voltage. The preset voltage can be set as needed and implemented through the circuit. For example, in one example, the preset voltage can be AC ​​150V, i.e., 150V AC voltage.

[0025] The reference voltage circuit 60 is connected to the first optocoupler of the voltage detection circuit 50. The reference voltage circuit 60 is used to output different reference voltages under different conditions. Specifically, when the first optocoupler of the voltage detection circuit 50 is turned on, the reference voltage circuit 60 outputs a first reference voltage; when the first optocoupler is turned off, the reference voltage circuit 60 outputs a second reference voltage. The first reference voltage is greater than the second reference voltage. For example, in one example, the first reference voltage is 125mV and the second reference voltage is 87.5mV. The principle of reference voltage generation will be explained in detail below.

[0026] The current detection circuit 70 has an input side and an output side. The input side of the current detection circuit 70 is connected to the output circuit 20 and the reference voltage circuit 60, while the output side is connected to the controller 40. The current detection circuit 70 outputs a first feedback signal based on the load current of the output circuit 20 and the first reference voltage output by the reference voltage circuit 60, or outputs a second feedback signal based on the load current of the output circuit and the second reference voltage output by the reference voltage circuit 60. The first or second feedback signal is used to cause the controller 40 to adjust the drive signal of the switching unit 30 to limit the input power of the primary winding NP of the transformer, thereby limiting the output power of the secondary winding NS, and thus limiting the output power of the switching power supply.

[0027] In some embodiments, reference Figure 2 , Figure 2 This is a circuit example diagram of a power control circuit according to an embodiment of this application.

[0028] In practical applications, the input circuit 10 may include a rectifier circuit to rectify the input AC voltage into a DC voltage DC-HV, and then input the DC voltage DC-HV to the primary winding NP of the transformer T. The input circuit 10 may also include an input electrolytic capacitor EC1. One end (e.g., the positive terminal) of the input electrolytic capacitor EC1 is connected to the primary winding NP, and the other end (e.g., the negative terminal) is grounded, for example, connected to ground PGND. The voltage across the input electrolytic capacitor EC1 is the DC voltage DC-HV.

[0029] Output circuit 20 includes two output lines, one for outputting voltage VOUT+ and the other for forming ground VOUT GND. Output circuit 20 may also include an output electrolytic capacitor EC2. One end (e.g., positive terminal) of the output electrolytic capacitor EC2 is connected to the VOUT+ voltage output line, and the other end (e.g., negative terminal) is connected to ground VOUT GND.

[0030] One end of the primary winding NP of transformer T is used to input DC voltage DC-HV, and the other end is connected to switching unit Q1, which is the aforementioned switching unit 30. One end of the secondary winding NS of transformer T is connected to the VOUT+ voltage output line, for example, through diode D3. The anode of diode D3 is connected to one end of the secondary winding NS, and the cathode of diode D3 is connected to the VOUT+ voltage output line. The other end of the secondary winding NS is grounded, for example, connected to ground SGND.

[0031] In some embodiments, the switching unit Q1 is a MOSFET. The gate of MOSFET Q1 serves as the control terminal of the switching unit. The gate of MOSFET Q1 is connected to controller U1, which is the aforementioned controller 40. The drain of MOSFET Q1 is connected to the primary winding NP. The source of MOSFET Q1 is grounded, for example, connected to ground PGND through resistors R11 and R12, with R11 and R12 connected in parallel.

[0032] In some embodiments, the controller U1 includes a power supply port VDD, a ground port GND, a control port G, a chip select port CS, and a feedback port FB. The power supply port VDD is connected to a power source to power the controller U1. The ground port GND is grounded, for example, connected to ground PGND. The control port G is connected to the gate of the MOSFET Q1 and is used to output a drive signal to turn the MOSFET Q1 on or off. The chip select port CS is grounded, for example, connected to the source of the MOSFET Q1, and connected to ground PGND through parallel resistors R11 and R12. The feedback port FB is connected to the current detection circuit 70; the connection relationship of the feedback port FB will be described in detail below.

[0033] In some embodiments, the controller U1 can be powered by a transformer T. The transformer T further includes an auxiliary winding NX, which is coupled to the secondary winding NS and grounded; for example, one end of the auxiliary winding NX is connected to ground PGND. The auxiliary winding NX is used to obtain a coupling voltage based on the voltage of the secondary winding NS. The power supply port VDD of the controller U1 is connected to the other end of the auxiliary winding NX, so that the coupling voltage obtained by the auxiliary winding NX is input to the power supply port VDD to power the controller U1.

[0034] In some embodiments, a diode D4 is further provided between the power supply port VDD and the auxiliary winding NX, with the anode of the diode D4 connected to the auxiliary winding NX and the cathode of the diode D4 connected to the power supply port VDD.

[0035] In some embodiments, the power control circuit further includes an electrolytic capacitor EC3. One end of the electrolytic capacitor EC3 (e.g., the positive terminal) is connected between the power supply port VDD and the diode D4, and the other end (e.g., the negative terminal) is grounded, for example, connected to ground PGND. It is understood that the electrolytic capacitor EC3 can be used to filter the supply voltage input to the power supply port VDD, ensuring the stability of the supply voltage.

[0036] In some embodiments, reference Figure 2 The voltage detection circuit 30 includes a first voltage divider circuit and a first Zener diode U2.

[0037] The first voltage divider circuit is connected to the input circuit 10 and grounded. In one example, the first voltage divider circuit includes a first resistor R1, a second resistor R2, and a third resistor R3 connected in series. The first resistor R1 is connected to the input circuit 10, for example, connected to the positive terminal of the input electrolytic capacitor EC1. The third resistor R3 is grounded, for example, connected to ground PGND. The first resistor R1, the second resistor R2, and the third resistor R3 can divide the input DC voltage DC-HV.

[0038] The first Zener diode U2 is a three-terminal Zener diode with a reference terminal, an anode, and a cathode. The reference terminal of the first Zener diode U2 is connected to the first voltage divider circuit. In one example, the reference terminal of the first Zener diode U2 is connected between the second resistor R2 and the third resistor R3, so the voltage divided by the third resistor R3 can be input to the reference terminal of the first Zener diode U2.

[0039] The first optocoupler of the voltage detection circuit 30 includes a first light-emitting diode (LED) U4A and a first phototransistor U4B. The first optocoupler includes a first input side 41, a second input side 42, a first output side 43, and a second output side 44. The first input side 41 and the second input side 42 are the two ends of the first LED U4A; for example, the first input side 41 is the anode of the first LED U4A, and the second input side 42 is the cathode of the first LED U4A. The first output side 43 and the second output side 44 are the two ends of the first phototransistor U4B; for example, the first output side 43 is the emitter of the first phototransistor U4B, and the second output side 44 is the collector of the first phototransistor U4B.

[0040] The anode of the first Zener diode U2 is grounded, for example, connected to ground PGND. The cathode of the first Zener diode U2 is connected to the second input side 42 of the first optocoupler, and the first input side 41 of the first optocoupler is connected to a power supply, for example, a 5V DC power supply. Figure 2 (This is represented as DC_5V). In one example, the first input side 41 is connected to a DC_5V power supply via resistor R13.

[0041] In some embodiments, the voltage detection circuit 30 further includes a step-down circuit. The step-down circuit includes a first diode D1 and a second Zener diode ZD1. The anode of the first diode D1 is connected to a first voltage divider circuit, for example, between a second resistor R2 and a third resistor R3. The cathode of the first diode D1 is connected to the cathode of the second Zener diode ZD1, and the anode of the second Zener diode ZD1 is connected to the reference terminal of the first Zener diode ZD2.

[0042] Understandably, in practical applications, the aforementioned preset voltage can be achieved through the voltage detection circuit 30, for example, by setting the preset voltage through the parameters of the first resistor R1, the second resistor R2, the third resistor R3, the first diode D1, the second Zener diode ZD1, and the first Zener diode U2.

[0043] For example, in one scenario, the preset voltage is AC 150V. This means the first optocoupler needs to conduct when the input voltage is greater than or equal to 150V and turn off when the input voltage is less than 150V. Assuming the internal reference voltage of the first Zener diode U2 is 2.5V, when the reference voltage of the first Zener diode U2 is greater than or equal to 2.5V, its anode and cathode conduct; when the reference voltage of the first Zener diode U2 is less than 2.5V, its anode and cathode are cut off. In this case, the following parameters can be set: R1 = 120kΩ, R2 = 128.7kΩ, R3 = 10kΩ, the voltage drop of the first diode D1 is 0.6V, and the voltage drop of the second Zener diode ZD1 is 5.1V. When the first Zener diode U2 conducts, the reference voltage needs to reach 2.5V, so the voltage across the third resistor R3 needs to reach 0.6V + 5.1V + 2.5V = 8.2V. Therefore, the voltage input to the electrolytic capacitor EC1 needs to reach ((R1+R2) / R3+1)*8.2V=212V. This 212V voltage is the rectified DC voltage, which is 212V / R3+1 in AC format. =150V.

[0044] In some embodiments, reference Figure 2The reference voltage circuit 60 includes a third Zener diode U3 and a second voltage divider circuit. The third Zener diode U3 is a three-terminal Zener diode with a reference terminal, an anode, and a cathode. The anode of the third Zener diode U3 is grounded, for example, connected to ground SGND. The cathode of the third Zener diode U3 is connected to a power supply, for example, connected to a 5V power supply through resistor R10. Figure 2 (This is represented as VCC_5V). Resistor R10 can serve to reduce voltage and limit current.

[0045] The second voltage divider circuit includes a fourth resistor R4, a fifth resistor R5, and a sixth resistor R6. The first terminal of the fourth resistor R4 is connected to the first terminal of the sixth resistor R6 and then to a power supply; for example, the fourth resistor R4 and the sixth resistor R6 are connected to a 5V power supply via resistor R10. The second terminal of the sixth resistor R6 is connected to the second output side 44 of the first optocoupler, for example, to the collector of the first phototransistor U4B. The reference terminal of the third Zener diode U3, the second terminal of the fourth resistor R4, the first terminal of the fifth resistor R5, and the first output side 43 of the first optocoupler are connected to a common node P. The common node P is used to output either the first or second reference voltage. The first reference voltage can be represented as Vref1, and the second reference voltage can be represented as Vref2. The voltage at the common node P can also be understood as the voltage of the reference terminal of the third Zener diode U3. The second terminal of the fifth resistor R5 is grounded, for example, connected to ground SGND.

[0046] When the first optocoupler is off, the first phototransistor U4B is off, the sixth resistor R6 forms an open circuit, and the voltage output at the common node P is the voltage obtained by dividing the voltage of the fifth resistor R5, which is the second reference voltage Vref2. When the first optocoupler is on, the first phototransistor U4B is on, the fourth resistor R4 and the sixth resistor R6 are connected in parallel, and the voltage output at the common node P is also the voltage obtained by dividing the voltage of the fifth resistor R5, which is the first reference voltage Vref1. It can be understood that the resistance value of the fourth resistor R4 and the sixth resistor R6 in parallel is less than the resistance value of the fourth resistor R4. Therefore, the voltage obtained by dividing the voltage of the fifth resistor R5 when the first phototransistor U4B is on is greater than the voltage obtained by dividing the voltage of the fifth resistor R5 when the first phototransistor U4B is off. That is, the first reference voltage Vref1 corresponding to the first optocoupler being on is greater than the second reference voltage Vref2 corresponding to the first optocoupler being off.

[0047] For example, in one scenario, R4 = 2.76kΩ, R5 = 100R (i.e., 100Ω), and R6 = 6.1kΩ, with a power supply voltage of 5V. When the first phototransistor U4B is off, the second reference voltage Vref2 can be calculated as 87.5mV from the voltage divider across R5. When the first phototransistor U4B is on, the parallel resistance of R4 and R6 is 1.9kΩ, and the first reference voltage Vref1 can be calculated as 125mV from the voltage divider across R5.

[0048] In some embodiments, continue to refer to Figure 2 The current detection circuit 70 includes a sampling resistor R7 and a comparator U6.

[0049] In this circuit, the sampling resistor R7 is connected in series in the output circuit 20, for example, in series with the ground line VOUT GND of the output circuit 20. The load current flows through the sampling resistor R7. Therefore, the sampling resistor R7 can obtain the sampled voltage based on the load current. The sampled voltage can be represented as V0. In some embodiments, the resistance value of the sampling resistor R7 is 25mR (25mΩ).

[0050] Comparator U6 includes a first input terminal 61, a second input terminal 62, and an output terminal 63. The first input terminal 61 is connected to the reference voltage circuit 60, for example, to the common node P of the reference voltage circuit 60, and is used to input either the first reference voltage Vref1 or the second reference voltage Vref2 (the first or second reference voltage is...). Figure 2 (Vref is used as an denoted symbol). The second input terminal 62 is connected to the sampling resistor R7 and is used to input the aforementioned sampling voltage V0. For example, in practical applications, the second input terminal 62 can be connected to the end of the sampling resistor R7 closest to the load, and the other end of the sampling circuit R7 can be grounded, for example, connected to ground SGND. The output terminal 63 is used to output the aforementioned first feedback signal or second feedback signal.

[0051] In some embodiments, such as Figure 2 As shown, the first input terminal 61 of comparator U6 is a non-inverting input (+), and the second input terminal 62 is an inverting input (-). Specifically, when the first reference voltage Vref1 is greater than the sampling voltage V0, the comparator's output terminal 63 outputs a low level as a first feedback signal. When the second reference voltage Vref2 is greater than the sampling voltage V0, the comparator's output terminal 63 outputs a low level as a second feedback signal. When the first reference voltage Vref1 is less than or equal to the sampling voltage V0, or when the second reference voltage Vref2 is less than or equal to the sampling voltage V0, the comparator's output terminal 63 outputs a high level.

[0052] In some embodiments, comparator U6 further includes a voltage terminal 64 and a ground terminal 65. Voltage terminal 64 is connected to a power supply, for example, to a 5V power supply. Figure 2 The voltage level (represented as VCC_5V) is used to power comparator U6. Ground terminal 65 is grounded, for example, connected to ground SGND.

[0053] Understandably, since the first input terminal 61 of comparator U6 can input two different reference voltages, namely the first reference voltage Vref1 or the second reference voltage Vref2, when the output terminal 63 outputs a low level, there are also two corresponding sampling voltages V0, that is, there are two corresponding load currents, and therefore two corresponding output powers. Therefore, the embodiments of this application can trigger corresponding control for the two output powers of the switching power supply respectively.

[0054] In some embodiments, the current detection circuit 70 further includes a second optocoupler. The second optocoupler includes a second light-emitting diode (LED) U5A and a second phototransistor U5B. The second optocoupler includes a first input side 51, a second input side 52, a first output side 53, and a second output side 54. The first input side 51 and the second input side 52 are the two ends of the second LED U5A; for example, the first input side 51 is the anode of the second LED U5A, and the second input side 52 is the cathode of the second LED U5A. The first output side 53 and the second output side 54 are the two ends of the second phototransistor U5B; for example, the first output side 53 is the emitter of the second phototransistor U5B, and the second output side 54 is the collector of the second phototransistor U5B.

[0055] The first input side 51 of the second optocoupler is connected to a power supply, for example, through a resistor R14 connected to the secondary winding NS of transformer T, using the output voltage of the secondary winding NS as the power supply. The second input side 52 of the second optocoupler is connected to the output terminal 63 of comparator U6. The first output side 53 of the second optocoupler is grounded, for example, connected to ground PGND. The second output side 54 of the second optocoupler is connected to controller U1, for example, to the feedback port FB of controller U1.

[0056] When the output terminal 63 of comparator U6 outputs a low level, i.e., when the first or second feedback signal is output, the second LED U5A and the second phototransistor U5B are turned on, i.e., the second optocoupler is turned on. This pulls down the voltage at the feedback port FB of controller U1, triggering feedback regulation of controller U1. For example, it reduces the duty cycle of the PWM drive signal output from control port G to limit the input power of the primary winding NP, thereby limiting the output power of the secondary winding NS, thus limiting the output power of the switching power supply. When the output terminal 63 of comparator U6 outputs a high level, the second LED U5A is turned off, the second phototransistor U5B is also turned off, i.e., the second optocoupler is turned off, and the feedback port FB of controller U1 is high. At this time, feedback regulation is not triggered.

[0057] In some embodiments, the current detection circuit 70 further includes a second diode D2. The anode of the second diode D2 is connected to the second input side 52 of the second optocoupler, i.e., to the cathode of the second light-emitting diode U5A. The cathode of the second diode D2 is connected to the output terminal 63 of the comparator U6. Understandably, the second diode D2 prevents reverse current flow, ensuring that the second light-emitting diode U5A only conducts when the output terminal 63 of the comparator U6 outputs a low level.

[0058] In some embodiments, the current detection circuit 70 further includes a fourth Zener diode U4, a resistor R15, and a resistor R16. Resistors R15 and R16 are connected in series, with one end of the series connection connected to the secondary winding NS of the transformer T, and the other end grounded, for example, connected to ground SGND.

[0059] The fourth Zener diode U4 is also a three-terminal Zener diode, having a reference electrode, an anode, and a cathode. The cathode of the fourth Zener diode U4 is connected to the second input side 52 of the second optocoupler. The anode of the fourth Zener diode U4 is grounded, for example, connected to ground SGND. The reference electrode of the fourth Zener diode U4 is connected between resistors R15 and R16.

[0060] In the power control circuit of this application embodiment, taking a preset voltage of 150V AC voltage as an example, its working principle is as follows: Under low-voltage input conditions: When the input voltage of input circuit 10 is less than the preset voltage (AC 150V), the input voltage is rectified to obtain a DC voltage, and the voltage of input electrolytic capacitor EC1 is less than 212V (AC 150V rectified to DC 212V). At this time, the voltage obtained by voltage division by the third resistor R3 is stepped down by the first diode D1 and the second Zener diode ZD1, and the voltage input to the reference terminal of the first Zener diode U2 is less than 2.5V (the reference voltage inside the first Zener diode U2 is set to 2.5V). The first Zener diode U2 is cut off, and the first optocoupler is turned off. The reference voltage circuit 60 outputs the second reference voltage Vref2, which is, for example, 87.5mV. Comparator U6 compares the second reference voltage Vref2 (87.5mV) with the sampled voltage V0. When the sampled voltage V0 is greater than 87.5mV, comparator U6 outputs a low level as a second feedback signal, turning on the second optocoupler. This pulls down the voltage at the feedback port FB of controller U1, triggering the feedback regulation of controller U1 to limit the output power of the switching power supply. Specifically, when the output voltage of the switching power supply is set to 20V, and the sampled voltage V0 is greater than 87.5mV, the corresponding load current is greater than 3.5A (with the sampling resistor R7 set to 25mΩ), and the output power of the switching power supply is greater than 70W. When the output power is less than 70W, the feedback regulation of controller U1 is not triggered. Therefore, it is possible to limit the output power of the switching power supply to a lower level (e.g., limited to 70W) under low-voltage input (input voltage less than 150V).

[0061] Under high-voltage input: When the input voltage of input circuit 10 is greater than or equal to the preset voltage (AC 150V), the input voltage is rectified to obtain a DC voltage, and the voltage of input electrolytic capacitor EC1 is greater than or equal to 212V (AC 150V rectified to DC 212V). At this time, the voltage obtained by voltage division by the third resistor R3 is stepped down by the first diode D1 and the second Zener diode ZD1, and the voltage input to the reference terminal of the first Zener diode U2 is greater than or equal to 2.5V (the reference voltage inside the first Zener diode U2 is set to 2.5V). The first Zener diode U2 is turned on, and the first optocoupler is turned on. The reference voltage circuit 60 outputs the first reference voltage Vref1, which is, for example, 125mV. Comparator U6 compares the first reference voltage Vref1 (125mV) with the sampled voltage V0. When the sampled voltage V0 is greater than 125mV, comparator U6 outputs a low level as the first feedback signal, turning on the second optocoupler. This pulls down the voltage at the feedback port FB of controller U1, triggering the feedback regulation of controller U1 to limit the output power of the switching power supply. Specifically, when the output voltage of the switching power supply is set to 20V, and the sampled voltage V0 is greater than 125mV, the corresponding load current is greater than 5A (with the sampling resistor R7 set to 25mΩ), and the output power of the switching power supply is greater than 100W. When the output power is less than 100W, the feedback regulation of controller U1 is not triggered. Therefore, it is possible to limit the output power of the switching power supply to a higher level (e.g., limited to 100W) under high-voltage input (input voltage greater than or equal to 150V).

[0062] Therefore, the power control circuit of this application embodiment can limit different output power for the low-voltage input and high-voltage input of the switching power supply respectively. The maximum output power of the switching power supply is less than that of the switching power supply when the low-voltage input is less than that when the high-voltage input is less, which can reduce the heat generation of the switching power supply when the low-voltage input is less. Therefore, no additional temperature treatment measures are needed for the low-voltage input case, thereby reducing costs.

[0063] This application also provides a switching power supply, which can be such as a charger or power adapter. The switching power supply includes the power control circuit of any of the above embodiments.

[0064] In the description of this application, it should be understood that terms such as “first” and “second” are used only to distinguish similar objects and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated.

[0065] It should be noted that in the embodiments of this application, "connection" can be understood as electrical connection. The connection between two electrical components can be a direct or indirect connection between the two electrical components. For example, the connection between A and B can be a direct connection between A and B, or an indirect connection between A and B through one or more other electrical components.

[0066] The power control circuit and switching power supply of the present application have been described in detail above. Specific examples have been used to illustrate the principles and implementation methods of this application. The descriptions of the above embodiments are only for the purpose of helping to understand this application. Furthermore, those skilled in the art will recognize that, based on the ideas of this application, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of this application.

Claims

1. A power control circuit for a switching power supply, characterized in that, include: A transformer includes a primary winding and a secondary winding coupled to each other. The primary winding is connected to an input circuit and a switching unit. The control terminal of the switching unit is connected to a controller. The secondary winding is connected to an output circuit. A voltage detection circuit is connected to the input circuit. The voltage detection circuit includes a first optocoupler. The first optocoupler is turned on when the input voltage of the input circuit is greater than or equal to a preset voltage, and the first optocoupler is turned off when the input voltage is less than the preset voltage. A reference voltage circuit is connected to the first optocoupler. When the first optocoupler is turned on, the reference voltage circuit outputs a first reference voltage. When the first optocoupler is turned off, the reference voltage circuit outputs a second reference voltage. The first reference voltage is greater than the second reference voltage. A current detection circuit is provided, wherein the input side of the current detection circuit is connected to the output circuit and the reference voltage circuit, and the output side of the current detection circuit is connected to the controller. The current detection circuit outputs a first feedback signal based on the load current of the output circuit and the first reference voltage, or outputs a second feedback signal based on the load current of the output circuit and the second reference voltage. The first feedback signal or the second feedback signal is used to enable the controller to adjust the drive signal of the switching unit to limit the input power of the primary winding.

2. The power control circuit according to claim 1, characterized in that, The voltage detection circuit includes: The first voltage divider circuit is connected to the input circuit and grounded; The first Zener diode has its reference electrode connected to the first voltage divider circuit, its anode grounded, its cathode connected to the second input side of the first optocoupler, and its first input side connected to a power supply.

3. The power control circuit according to claim 2, characterized in that, The voltage detection circuit further includes a step-down circuit, which includes a first diode and a second Zener diode. The anode of the first diode is connected to the first voltage divider circuit, the cathode of the first diode is connected to the cathode of the second Zener diode, and the anode of the second Zener diode is connected to the reference electrode of the first Zener diode.

4. The power control circuit according to claim 2, characterized in that, The first voltage divider circuit includes a first resistor, a second resistor, and a third resistor connected in series. The first resistor is connected to the input circuit, the third resistor is grounded, and the reference terminal of the first Zener diode is connected between the second resistor and the third resistor.

5. The power control circuit according to claim 1, characterized in that, The reference voltage circuit includes: The third Zener diode has its anode grounded and its cathode connected to the power supply. The second voltage divider circuit includes a fourth resistor, a fifth resistor, and a sixth resistor. The first terminal of the fourth resistor is connected to the first terminal of the sixth resistor and connected to a power supply. The second terminal of the sixth resistor is connected to the second output side of the first optocoupler. The reference terminal of the third Zener diode, the second terminal of the fourth resistor, the first terminal of the fifth resistor, and the first output side of the first optocoupler are connected to a common node. The common node is used to output the first reference voltage or the second reference voltage. The second terminal of the fifth resistor is grounded.

6. The power control circuit according to claim 1, characterized in that, The current detection circuit includes: A sampling resistor is connected in series in the output circuit, and the sampling resistor obtains the sampling voltage based on the load current. The comparator has a first input terminal connected to the reference voltage circuit for inputting the first reference voltage or the second reference voltage, a second input terminal connected to the sampling resistor for inputting the sampling voltage, and an output terminal for outputting the first feedback signal or the second feedback signal.

7. The power control circuit according to claim 6, characterized in that, The current detection circuit further includes a second optocoupler. The first input side of the second optocoupler is connected to the power supply, the second input side of the second optocoupler is connected to the output terminal of the comparator, the first output side of the second optocoupler is grounded, and the second output side of the second optocoupler is connected to the controller.

8. The power control circuit according to claim 7, characterized in that, The current detection circuit further includes a second diode, the anode of which is connected to the second input side of the second optocoupler, and the cathode of which is connected to the output terminal of the comparator.

9. The power control circuit according to claim 6, characterized in that, The first input terminal of the comparator is the non-inverting input terminal, and the second input terminal of the comparator is the inverting input terminal; When the first reference voltage is greater than the sampling voltage, the comparator outputs a low level as the first feedback signal; When the second reference voltage is greater than the sampling voltage, the comparator outputs a low level as the second feedback signal.

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

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