Voltage stabilizing circuit and switching power supply

Abstract

The utility model discloses a voltage stabilizing circuit and a switching power supply. The voltage stabilizing circuit comprises a sampling resistor Rsense; one end of the Rsense is connected with one end of the resistor R1; the other end of the Rsense is connected with one end of a resistor R2; the other end of the R1 is respectively connected with the inverting input end of the operational amplifier U1 and one end of the resistor R3; the other end of the R2 is connected with the in-phase input end of the U1; the output end of U1 is respectively connected with the other end of R3 and one end of a resistor R4; the other end of the R4 is connected with a first pin of the optocoupler U2; a third pin of the U2 is respectively connected with a signal ground of the PWM controller and one end of a timing resistor Rt; the fourth pin of the U2 is connected with the RT pin of the PWM controller and the other end of the Rt; the CT pin of the PWM controller is connected with one end of the timing capacitor Ct; and the other end of the Ct is in signal ground connection with the PWM controller. The circuit can adapt to a PWM type controller, adjusts the switching frequency according to the magnitude of the load current, and reduces the switching loss of a switching tube.

Description

Technical Field

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

[0002] Currently, pulse width modulation (PWM) is the main modulation method for power conversion in switching power supplies.

[0003] Pulse Width Modulation (PWM) controllers are widely used, and the frequency of the output drive signal is generally fixed. As a result, switching power supplies using this control method (i.e., those using PWM controllers) still output at a fixed frequency when the output is lightly loaded or unloaded, which results in greater switching losses on the switching transistors and limits the overall efficiency of the switching power supply.

[0004] Therefore, there is an urgent need to develop a technology that can solve the above-mentioned technical problems. Utility Model Content

[0005] The purpose of this invention is to address the technical deficiencies of existing technologies by providing a voltage regulator circuit and a switching power supply.

[0006] Therefore, this utility model provides a voltage regulator circuit, which includes: a sampling circuit, an optocoupler U2, a timing resistor Rt, a timing capacitor Ct, and a PWM controller;

[0007] The sampling circuit includes sampling resistor Rsense, resistor R1, resistor R2, resistor R3, and operational amplifier U1.

[0008] One end of the sampling resistor Rsense is connected to one end of the resistor R1;

[0009] The other end of the sampling resistor Rsense is connected to one end of the resistor R2;

[0010] The other end of resistor R1 is connected to the inverting input terminal of operational amplifier U1 and one end of resistor R3, respectively.

[0011] The other end of resistor R2 is connected to the non-inverting input of operational amplifier U1;

[0012] The output terminal of operational amplifier U1 is connected to the other end of resistor R3 and one end of resistor R4, respectively;

[0013] The other end of resistor R4 is connected to pin 1 of optocoupler U2;

[0014] Pin 2 of optocoupler U2 is grounded.

[0015] Pin 3 of optocoupler U2 is connected to the signal ground of the PWM controller and one end of the timing resistor Rt, respectively.

[0016] Pin 4 of optocoupler U2 is connected to the RT pin of the PWM controller and the other end of the timing resistor Rt, respectively.

[0017] The CT pin of the PWM controller is connected to one end of the timing capacitor Ct;

[0018] The other end of the timing capacitor Ct is connected to the signal ground of the PWM controller.

[0019] In addition, this utility model also provides a switching power supply, which includes the voltage regulator circuit as described above.

[0020] As can be seen from the technical solution provided by this utility model above, compared with the prior art, this utility model provides a voltage regulator circuit and a switching power supply with a scientific design. The voltage regulator circuit can adapt to PWM controllers (specifically, PWM controllers used in switching power supplies for power conversion modulation). Without changing the voltage and current feedback of the original PWM controller, it can adjust the switching frequency according to the load current (the switching frequency is high when the load current is large, which can reduce the size of the magnetic components; the switching frequency is reduced under light load or no load, which reduces the switching loss of the switching transistor), thereby significantly reducing the switching loss of the switching transistor and improving the overall efficiency of the switching power supply using the PWM controller, which has significant practical significance.

[0021] The voltage regulator circuit of this invention is a pulse frequency modulation voltage regulator circuit, which can use a general PWM controller to achieve pulse frequency modulation (PFM), so that the driving frequency of the switching transistor can be automatically adjusted. The frequency is higher when the load is larger and lower when there is no load, which significantly reduces the no-load loss and thus improves the efficiency of the switching power supply using the PWM controller. Attached Figure Description

[0022] Figure 1 An electrical schematic diagram of a voltage regulator circuit provided by this utility model. Detailed Implementation

[0023] 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.

[0024] In the description of this patent, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "setting" should be interpreted broadly. For example, they can refer to a fixed connection or setting, a detachable connection or setting, or an integral connection or setting. Those skilled in the art can understand the specific meaning of the above terms in this patent according to the specific circumstances.

[0025] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this utility model, "a plurality of" means two or more, unless otherwise explicitly specified.

[0026] See Figure 1 This utility model provides a voltage regulator circuit, which is a novel pulse frequency modulation voltage regulator circuit, including: a sampling circuit, an optocoupler U2, a timing resistor Rt, a timing capacitor Ct, and a PWM controller;

[0027] The sampling circuit includes sampling resistor Rsense, resistor R1, resistor R2, resistor R3, and operational amplifier U1.

[0028] One end of the sampling resistor Rsense is connected to one end of the resistor R1;

[0029] The other end of the sampling resistor Rsense is connected to one end of the resistor R2;

[0030] The other end of resistor R1 is connected to the inverting input terminal (i.e., pin 1) of operational amplifier U1 and one end of resistor R3, respectively.

[0031] The other end of resistor R2 is connected to the non-inverting input terminal (i.e., pin 2) of operational amplifier U1;

[0032] The output terminal (i.e., pin 3) of operational amplifier U1 is connected to the other end of resistor R3 and one end of resistor R4, respectively;

[0033] The other end of resistor R4 is connected to pin 1 of optocoupler U2 (i.e., the anode of the light-emitting diode inside optocoupler U2);

[0034] It should be noted that, for this utility model, the sampling circuit is implemented using a differential amplifier circuit. After sampling and amplifying the output current of the switching power supply, the sampled current is connected to the anode of the light-emitting diode in the optocoupler U2 through the output terminal of the amplifier (operational amplifier U1).

[0035] Pin 2 of optocoupler U2 (the cathode of the LED inside optocoupler U2) is grounded.

[0036] Pin 3 of optocoupler U2 (i.e. the emitter of the phototransistor inside optocoupler U2) is connected to the signal ground of the PWM controller and one end of the timing resistor Rt, respectively.

[0037] Pin 4 of optocoupler U2 (i.e. the collector of the phototransistor inside optocoupler U2) is connected to the RT pin of the PWM controller (i.e. the timing resistor pin) and the other end of the timing resistor Rt, respectively.

[0038] The CT pin (i.e., the timing capacitor pin) of the PWM controller is connected to one end of the timing capacitor Ct;

[0039] The other end of the timing capacitor Ct is connected to the signal ground of the PWM controller.

[0040] In this invention, specifically, the sampling resistor Rsense is connected to the switching power supply 100 and is used to sample the DC output current of the switching power supply 100.

[0041] It should be noted that the sampling resistor Rsense is the sampling resistor for the DC output current.

[0042] In practice, the sampling resistor Rsense is set on the connection line between the voltage output terminal Vout of the switching power supply 100 and the voltage input terminal of the load F.

[0043] Furthermore, the voltage output terminal Vout of the switching power supply includes the positive output terminal L+ and the negative output terminal L- on the switching power supply 100;

[0044] The voltage input terminals of the load F include the positive input terminal DC+ and the negative input terminal DC- on the load F;

[0045] The positive output terminal L+ of the switching power supply 100 is connected to the positive input terminal DC+ of the load F;

[0046] A sampling resistor Rsense is provided on the connection line between the positive output terminal L+ on the switching power supply 100 and the positive input terminal DC+ on the load F.

[0047] The negative output terminal L- of the switching power supply 100 is connected to the negative input terminal DC- on the load F.

[0048] In this invention, specifically, the second pin of the optocoupler U2 (the cathode of the light-emitting diode inside the optocoupler U2) is connected to the signal ground of the switching power supply 100.

[0049] It should be noted that the switching power supply 100 is connected to the external AC power grid (AC220V AC power grid) and is used to convert the AC voltage input from the external AC power grid into a direct voltage and output it to the load F.

[0050] In practical implementation, the switching power supply 100 can be used to provide AC 165-275V input and DC 24V or DC 48V output to the load F, supplying DC power (e.g., DC 24V). It should be noted that the switching power supply 100 is a mature and widely used existing power supply technology. For example, it could be a switching power supply module, model MW1-Z24 / 60, manufactured by Tianjin Railway Signal Co., Ltd., capable of AC 165-275V input and DC 24V output.

[0051] In this invention, specifically, the operational amplifier U1 is a mature and widely used electrical component, such as an LM258 operational amplifier manufactured by Texas Instruments (TI) or STMicroelectronics (ST), which is a general-purpose operational amplifier capable of amplifying error signals.

[0052] It should be noted that for operational amplifier U1, pin 1 is the inverting input terminal, and for the inverting input terminal, the polarity of the input signal change at this terminal is opposite to that at the output terminal; pin 2 is the non-inverting input terminal, and for the non-inverting input terminal, the polarity of the input signal change at this terminal is the same as that at the output terminal; pin 3 is the operational output terminal. Operational amplifier U1 is used to amplify the difference signal between the non-inverting input terminal and the inverting input terminal and output it to the operational output terminal.

[0053] It should be noted that pins 1 and 2 of operational amplifier U1 are connected to resistors R1 and R2 respectively to acquire the voltage difference signal across the sampling resistor Rsense. Resistor R3, connected between pins 2 and 3 of operational amplifier U1, forms the feedback amplification loop of the operational amplifier, used to amplify the voltage difference signal across Rsense. Pin 3 of operational amplifier U1 is connected to pin 1 of optocoupler U2, i.e., to the anode of the LED inside optocoupler U2. When the voltage signal at pin 3 of operational amplifier U1 changes, the light intensity of the LED inside optocoupler U2 changes accordingly. Therefore, when the voltage difference across the sampling resistor Rsense changes, the light intensity of the LED in optocoupler U2 will change accordingly. That is, the greater the current flowing through the sampling resistor Rsense, the greater the voltage difference across Rsense, and the greater the light intensity of the LED in optocoupler U2; conversely, the smaller the current, the greater the light intensity.

[0054] In this invention, specifically, the optocoupler U2 is a mature and widely used electrical component. For example, the optocoupler U2 can be an EL817 optocoupler product manufactured by Everlight Electronics Co., Ltd., or a general-purpose optocoupler product manufactured by other companies. In the circuit of this invention, it is used to isolate the output voltage signal of the operational amplifier U1 and convert the change in input voltage into a change in the output impedance of the phototransistor inside the optocoupler.

[0055] It should be noted that for optocoupler U2, pin 1 is the LED anode (positive terminal), which is the anode of the light-emitting diode in the optocoupler, used to receive the input signal and convert it into a light signal; pin 2 is the LED cathode (negative terminal), which is the cathode of the light-emitting diode, used to complete the circuit loop of the light-emitting diode; pin 3 is the photodetector emitter (E terminal), which is connected to the emitter of the photodetector and used to output an electrical signal; pin 4 is the photodetector collector (C terminal), which is connected to the collector of the photodetector and used to receive the light signal and convert it into an electrical signal for output.

[0056] It should be noted that pin 1 of optocoupler U2 is connected to the output pin (i.e., pin 3) of operational amplifier U1, and is used to convert the voltage signal output by operational amplifier U1 into an optical signal; pin 2 of optocoupler U2 is connected to signal ground, forming the circuit loop of the light-emitting diode; pin 3 of optocoupler U2 is connected to signal ground, forming the circuit loop of the phototransistor; pin 4 of optocoupler U2 is connected to the timing resistor Rt. By changing the conduction strength of the optocoupler, the resistance value of the timing resistor pin RT of the PWM controller is affected, thereby changing the output clock pulse frequency of the oscillator inside the PWM controller, and thus controlling the frequency of the output drive signal of the PWM controller.

[0057] In this invention, the sampling resistor Rsense is connected in series between the output circuit of the power module (i.e., the switching power supply 100) and the load. When the load current flows through the sampling resistor Rsense, a voltage difference is generated across the sampling resistor Rsense. Resistors R1, R2, and R3, along with operational amplifier U1, constitute a typical differential amplifier circuit, which amplifies the voltage difference generated across the sampling resistor Rsense to drive the light-emitting diode in the optocoupler U2 to change its light emission. The timing resistor Rt and the timing capacitor Ct are the timing devices of the PWM controller. The values ​​of the timing resistor Rt and the timing capacitor Ct determine the output clock frequency of the oscillator inside the PWM controller, and thus the output drive frequency of the PWM controller.

[0058] In this invention, specifically, the sampling resistor Rsense, resistors R1, R2, R3, and R4, the timing resistor Rt, and the timing capacitor Ct are all conventional components. The specific values ​​of these resistors and capacitors are related to the output power of the specific power supply. Generally, the value of the sampling resistor Rsense ranges from a few milliohms to several hundred milliohms, selected according to the rated current of the load, so that the power loss generated on the sampling resistor Rsense is minimized. At the same time, the voltage signal output by the operational amplifier U1 is sufficient to drive the light-emitting diode of the optocoupler U2, so that the current signal flowing through the light-emitting diode is in the range of 1mA-10mA.

[0059] In practical implementation, taking a switching power supply with a rated output current of 10A as an example, the sampling resistor Rsense can be set to 10mΩ, resistors R1 and R2 are both 10kΩ, resistor R3 is 100kΩ, and resistor R4 is 100Ω. When the power supply outputs 10A, the voltage difference across the sampling resistor Rsense is U = I * R = 0.1V. The maximum output voltage of operational amplifier U1 is 1V, and the maximum current flowing through the LED in optocoupler U2 through current-limiting resistor R4 does not exceed 10mA. When the output current of the power module (i.e., switching power supply 100) varies within the range of 0-10A, the current flowing through the LED in optocoupler U2 also varies within the range of 0-10mA. Of course, depending on the different rated currents of different switching power supplies, different resistor values ​​can be selected for sampling the output current, ultimately controlling the current flowing through the LED in the optocoupler to vary within the range of 0-10mA.

[0060] In this invention, specifically, the output terminal OUT of the PWM controller is connected to the switching transistor Q1 (which is the original switching transistor in the switching power supply 100) through the driving resistor R5.

[0061] It should be noted that the switching transistor Q1 is the original switching transistor in the switching power supply 100, which is used to control the conduction and cutoff of the main circuit (i.e., the output circuit) of the switching power supply 100, and realize the power conversion of the power supply.

[0062] In practice, the output terminal OUT of the PWM controller is connected to one end of the drive resistor R5;

[0063] The other end of the drive resistor R5 is connected to the gate G of the switching transistor Q1.

[0064] It should be noted that the PWM controller outputs a PWM drive signal, see... Figure 1 As shown, the OUT terminal (output pin) of the PWM controller is used to output the drive signal, and is typically connected to the drive electrode of the driven switching transistor through a drive resistor R5. See also... Figure 1As shown, the output terminal OUT of the driver (i.e., the PWM controller) is connected to the driving electrode of the switching transistor Q1, i.e., the gate of the MOSFET or IGBT, through the driving resistor R5.

[0065] It should be noted that the switching transistor Q1 can be a general-purpose MOSFET or IGBT. Taking MOSFET as an example, the switching transistor can be a commonly used ON Semiconductor FQP4N90C MOSFET or a STMicroelectronics STFW3N150 MOSFET. In a switching power supply, the switching transistor Q1 is used to turn the main circuit on and off, thereby achieving power conversion.

[0066] It should be noted that MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor) is a key electronic component widely used in electronic devices, playing a particularly important role in power management and power conversion.

[0067] exist Figure 1 In this diagram, the switching transistor Q1 is a MOSFET. Q1 has three pins: pin 1 is the gate (G), pin 2 is the drain (D), and pin 3 is the source (S). Gate (G): The gate is the key pin controlling the MOSFET's on / off state, controlling the current between the source and drain through the electric field effect. Source (S): The source is the primary endpoint from which current flows out. Drain (D): The drain is the other primary endpoint from which current flows in or out, opposite to the source.

[0068] exist Figure 1 In this configuration, one end of the drive resistor R5 is connected to the output terminal OUT of the PWM controller, and the other end of the drive resistor R5 is connected to pin 1 (gate) of the switching transistor Q1. Pins 2 and 3 of the switching transistor Q1 are connected to other locations in the main circuit of the switching power supply. For example, pin 2 of the switching transistor Q1 can be connected to energy storage components such as transformers or inductors, and pin 3 of the switching transistor Q1 can be connected to ground. Depending on the specific topology of the switching power supply, pins 2 and 3 of different switching transistors can have different connection methods. It should be noted that the specific connection methods of the switching transistors in the switching power supply are common knowledge in existing switching power supplies and will not be elaborated here.

[0069] In this invention, specifically, the PWM controller is a general-purpose controller widely used as a control chip in switching power supplies. Its main function is to control the on and off of the switching transistor by adjusting the pulse width, thereby achieving precise power control. There are many common manufacturers and models of PWM controllers, such as Texas Instruments (TI) models like TL494, UC3846, and LM3409; and On Semiconductor models like NCP1252 and NCP1034.

[0070] It should be noted that the pinout of the PWM controller varies considerably depending on the specific model. In this invention, the main PWM controller pins used are RT, CT, and OUT. The RT pin is the timing resistor pin, used to set the oscillator frequency; the CT pin is the timing capacitor pin, used to set the oscillator frequency; and the OUT pin is the PWM drive signal output pin, used to output the drive signal generated by the PWM controller, which drives the switching transistor to turn on and off. The device parameters of the RT and CT pins of the PWM controller determine the switching frequency of the OUT output pin.

[0071] In specific implementation, when the PWM controller uses the UC3846 chip mentioned above, in this 16-pin package structure, pin 8 is the defined CT pin, pin 9 is the defined RT pin, and pin 11 is the OUT pin. Figure 1 The pins RT, CT, and OUT of the controller are the pins (port names) defined on the specific PWM controller chip. The RT pin is the timing resistor pin, used to set the oscillator frequency; the CT pin is the timing capacitor pin, used to set the oscillator frequency; and the OUT pin is the PWM drive signal output pin, used to output the drive signal generated by the PWM controller to change the pulse width, which drives the switching transistor to turn on and off. The device parameters of the RT and CT pins of the PWM controller determine the switching frequency of the OUT output pin.

[0072] In this invention, specifically, the only pin associated with the voltage regulator circuit of this invention is the RT pin of the PWM controller. The fourth pin of the optocoupler U2 is connected to the RT pin of the PWM controller, and the third pin of the optocoupler U2 is connected to the ground (i.e., signal ground) of the PWM controller.

[0073] It should be noted that the output voltage of the pulse frequency modulation voltage regulator circuit provided by this utility model can be different voltage specifications such as DC 12V, 24V, 48V, etc.

[0074] Based on the voltage regulator circuit provided by this utility model, this utility model also provides a switching power supply, which includes the voltage regulator circuit as described above.

[0075] In this invention, specifically, the PWM controller in the voltage regulator circuit of the switching power supply provided by this invention is connected to the switching transistor Q1 (specifically, the original switching transistor in the switching power supply).

[0076] In practice, the output terminal OUT of the PWM controller is connected to the switching transistor Q1 through the driving resistor R5.

[0077] Furthermore, the output terminal OUT of the PWM controller is connected to one end of the drive resistor R5;

[0078] The other end of the drive resistor R5 is connected to the gate G (pin 1) of the switching transistor Q1.

[0079] It should be noted that the OUT pin of the PWM controller outputs a pulse-width-varying drive signal to turn the existing switching transistor in the switching power supply on and off. Specifically, the OUT pin of the PWM controller is connected to one end of the drive resistor R5, and the other end of the drive resistor R5 is connected to pin 1 (the gate) of the switching transistor Q1. The switching frequency of the drive signal output from the OUT pin of the PWM controller is controlled by the RT and CT pins of the PWM controller, and the duty cycle of the drive signal output from the OUT pin of the PWM controller is controlled by the existing switching power supply circuit. The drive signal output from the OUT pin of the PWM controller passes through the drive resistor R5, which limits the current of the drive signal to prevent the amplitude of the drive signal from being too high and damaging the switching transistor Q1.

[0080] In terms of specific implementation, it should be noted that the switching power supply of this utility model is basically the same as the switching power supply module of model MW1-Z24 / 60 produced by Tianjin Railway Signal Co., Ltd., the difference being: the addition of the following design... Figure 1 The voltage regulator circuit shown.

[0081] It should be noted that the switching power supply module, model MW1-Z24 / 60, manufactured by Tianjin Railway Signal Co., Ltd., can achieve AC input of 165~275V and DC output of 24V.

[0082] It should be noted that for switching power supplies, the switching transistor Q1 can be a general-purpose MOSFET or IGBT. Taking MOSFET as an example, the switching transistor can be a commonly used ON Semiconductor FQP4N90C MOSFET or a STMicroelectronics STFW3N150 MOSFET. The switching transistor Q1 in a switching power supply is used to turn the main circuit on and off, realizing power conversion.

[0083] To better understand the technical solution of this utility model, the working principle of this utility model is explained below.

[0084] The values ​​of the timing resistor Rt and timing capacitor Ct connected to the PWM controller determine the clock output frequency of the PWM controller's internal oscillator. This clock output frequency, in turn, determines the switching frequency of the switching transistors in the switching power supply. The PWM controller's internal oscillator is an RC oscillator. A larger product of the timing resistor Rt and the timing capacitor Ct results in a lower clock frequency for the RC oscillator and a lower output switching frequency; conversely, a smaller product of the timing resistor Rt and the timing capacitor Ct results in a higher clock frequency for the RC oscillator and a higher output switching frequency.

[0085] When the output current of the switching power supply 100 increases (i.e. the current required by the load F), the equivalent resistance between pins 3 and 4 of the optocoupler U2 decreases. Therefore, the total resistance after the equivalent resistance is connected in parallel with the timing resistor Rt decreases, the output clock frequency of the RC oscillator increases, and the output drive frequency (i.e. the drive frequency output by the PWM controller to the switching transistor) increases accordingly.

[0086] When the output current of the switching power supply 100 (i.e. the current required by the load F) decreases (e.g., under no-load conditions), the equivalent resistance between pins 3 and 4 of the optocoupler U2 increases. Therefore, the total resistance after the equivalent resistance is connected in parallel with the timing resistor Rt increases, the output clock frequency of the RC oscillator decreases, and the output drive frequency (i.e., the drive frequency output by the PWM controller to the switching transistor) increases accordingly.

[0087] In summary, based on the technical solution of this utility model, a sampling resistor for DC output current is adopted, which can realize pulse frequency modulation (PFM) control on the basis of a general PWM controller, thereby giving full play to the technical effect of the current pulse frequency modulation (PFM) control method. That is, the driving frequency provided by the PWM controller to the switching transistor can be automatically adjusted. The larger the load, the higher the driving frequency. When there is no load, the driving frequency is reduced, which can significantly reduce no-load loss.

[0088] Compared with the prior art, the voltage regulator circuit provided by this utility model has the following beneficial effects:

[0089] 1. This utility model can automatically adjust the driving frequency of the switching transistor according to the load change, which can improve the EMI (electromagnetic interference) characteristics of the switching power supply.

[0090] 2. The voltage regulator circuit of this utility model, as a novel pulse frequency modulation voltage regulator circuit, can be widely used in various types of controllers. The pulse frequency modulation control method can reduce the switching frequency of the switching transistor, extend the service life of power devices, and bring good economic and social benefits.

[0091] The above description is only a preferred embodiment of the present utility model. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present utility model, and these improvements and modifications should also be considered within the protection scope of the present utility model.

Claims

1. A voltage regulator circuit, characterized in that, include: Sampling circuit, optocoupler U2, timing resistor Rt, timing capacitor Ct, and PWM controller; The sampling circuit includes sampling resistor Rsense, resistor R1, resistor R2, resistor R3, and operational amplifier U1. One end of the sampling resistor Rsense is connected to one end of the resistor R1; The other end of the sampling resistor Rsense is connected to one end of the resistor R2; The other end of resistor R1 is connected to the inverting input terminal of operational amplifier U1 and one end of resistor R3, respectively. The other end of resistor R2 is connected to the non-inverting input of operational amplifier U1; The output terminal of operational amplifier U1 is connected to the other end of resistor R3 and one end of resistor R4, respectively; The other end of resistor R4 is connected to pin 1 of optocoupler U2; Pin 2 of optocoupler U2 is grounded; Pin 3 of optocoupler U2 is connected to the signal ground of the PWM controller and one end of the timing resistor Rt, respectively. Pin 4 of optocoupler U2 is connected to the RT pin of the PWM controller and the other end of the timing resistor Rt, respectively. The CT pin of the PWM controller is connected to one end of the timing capacitor Ct; The other end of the timing capacitor Ct is connected to the signal ground of the PWM controller.

2. The voltage regulator circuit as described in claim 1, characterized in that, The sampling resistor Rsense is connected to the switching power supply (100) and is used to sample the DC output current of the switching power supply (100).

3. The voltage regulator circuit as described in claim 1 or 2, characterized in that, The sampling resistor Rsense is placed on the connection line between the voltage output terminal of the switching power supply (100) and the voltage input terminal of the load F.

4. The voltage regulator circuit as described in claim 3, characterized in that, The voltage output terminal Vout of the switching power supply includes the positive output terminal L+ and the negative output terminal L- on the switching power supply (100); The voltage input terminals of the load F include the positive input terminal DC+ and the negative input terminal DC- on the load F; The positive output terminal L+ on the switching power supply (100) is connected to the positive input terminal DC+ on the load F; A sampling resistor Rsense is provided on the connection line between the positive output terminal L+ on the switching power supply (100) and the positive input terminal DC+ on the load F; The negative output terminal L- of the switching power supply (100) is connected to the negative input terminal DC- on the load F.

5. The voltage regulator circuit as described in any one of claims 2 to 4, characterized in that, Pin 2 of optocoupler U2 is connected to the signal ground of the switching power supply (100).

6. The voltage regulator circuit as described in any one of claims 2 to 4, characterized in that, The output terminal OUT of the PWM controller is connected to the original switching transistor Q1 in the switching power supply (100) through the drive resistor R5.

7. A switching power supply, characterized in that, Includes the voltage regulator circuit as described in any one of claims 1 to 6.

8. The switching power supply as described in claim 7, characterized in that, The PWM controller in the voltage regulator circuit is connected to the switching transistor Q1.

9. The switching power supply as described in claim 8, characterized in that, The output terminal OUT of the PWM controller is connected to the switching transistor Q1 through the drive resistor R5.

10. The switching power supply as described in claim 9, characterized in that, The output terminal OUT of the PWM controller is connected to one end of the drive resistor R5; The other end of the drive resistor R5 is connected to the gate G of the switching transistor Q1.

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