Voltage stabilizing circuit and switching power supply

Abstract

The invention 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, the switching frequency is adjusted according to the magnitude of the load current, and the switching loss of a switching tube is reduced.

Description

Technical Field

[0001] The present invention relates to the field of circuit technology, specifically to the field of switching power supply control circuit technology, and in particular to a voltage stabilizing circuit and a switching power supply. Background Art

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

[0003] Pulse width modulation (PWM) controllers are widely used. Generally, the frequency of the output drive signal is fixed. Therefore, the switching power supply that adopts this control method (i.e., using a PWM controller) still outputs at a fixed frequency when the output is lightly loaded or no-loaded, resulting in large switching losses on the switching tube, and the overall efficiency of the switching power supply is limited.

[0004] Therefore, there is an urgent need to develop a technology that can solve the above technical problems. Summary of the invention

[0005] The purpose of the present invention is to provide a voltage stabilizing circuit and a switching power supply in view of the technical defects in the prior art.

[0006] To this end, the present invention provides a voltage stabilizing circuit, which includes: a sampling circuit, an optical coupler U2, a timing resistor Rt, a timing capacitor Ct and a PWM controller;

[0007] Wherein, the sampling circuit includes a sampling resistor Rsense, a resistor R1, a resistor R2, a resistor R3 and an 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 the resistor R1 is connected to the inverting input end of the operational amplifier U1 and one end of the resistor R3 respectively;

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

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

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

[0014] The second pin of the optocoupler U2 is grounded.

[0015] The third pin of the optocoupler U2 is connected to the signal ground of the PWM controller and one end of the timing resistor Rt respectively;

[0016] The 4th pin of the 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, the present invention also provides a switching power supply, which includes the voltage stabilizing circuit as described above.

[0020] It can be seen from the technical solution provided by the present invention that, compared with the prior art, the present invention provides a voltage stabilizing circuit and a switching power supply with scientific design. The voltage stabilizing circuit can adapt to a PWM type controller (specifically, a PWM controller applied to a switching power supply for power conversion modulation in the switching power supply). On the basis of not changing the voltage and current feedback of the original PWM controller, the switching frequency can be adjusted according to the load current (when the load current is large, the switching frequency is high, which can reduce the volume of the magnetic component; when the load current is light or no-load, the switching frequency is controlled to be reduced to reduce the switching loss of the switching tube), thereby significantly reducing the switching loss of the switching tube, and further improving the overall efficiency of the switching power supply using the PWM controller, which has great practical significance.

[0021] The voltage stabilizing circuit of the present invention is a pulse frequency modulation voltage stabilizing circuit, which can use a general PWM controller to realize pulse frequency modulation (PFM), so that the driving frequency of the switching tube can be automatically adjusted. The greater the load, the higher the frequency, and the frequency is reduced when no-load, which significantly reduces the no-load loss, thereby improving the efficiency of the switching power supply using the PWM controller. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 An electrical schematic diagram of a voltage stabilizing circuit provided by the present invention. DETAILED DESCRIPTION

[0023] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0024] In the description of this patent, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", and "set" should be understood in a broad sense, for example, it can be fixedly connected or set, or it can be detachably connected or set, or connected or set in one piece. For ordinary technicians in this field, the specific meanings of the above terms in this patent can be understood according to specific circumstances.

[0025] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0026] See also Figure 1 , the present invention provides a voltage stabilizing circuit, which is a novel pulse frequency modulation voltage stabilizing circuit, comprising: a sampling circuit, an optical coupler U2, a timing resistor Rt, a timing capacitor Ct and a PWM controller;

[0027] Wherein, the sampling circuit includes a sampling resistor Rsense, a resistor R1, a resistor R2, a resistor R3 and an 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 the resistor R1 is connected to the inverting input end (i.e., the first pin) of the operational amplifier U1 and one end of the resistor R3 respectively;

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

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

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

[0034] It should be noted that, for the present invention, the sampling circuit is implemented using a differential amplifier circuit, which samples and amplifies the output current of the switching power supply and then connects the output end of the amplifier (operational amplifier U1) to the anode of the light-emitting diode in the optocoupler U2.

[0035] The second pin of the optocoupler U2 (the cathode of the light emitting diode inside the optocoupler U2) is grounded.

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

[0037] The 4th pin of the optocoupler U2 (i.e., the collector of the phototransistor inside the 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., 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 the present invention, in a specific implementation, 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 a sampling resistor of the DC output current.

[0042] In a specific implementation, the sampling resistor Rsense is arranged on a connection line between the voltage output terminal Vout of the switching power supply 100 and the voltage input terminal of the load F;

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

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

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

[0048] In the present invention, in a specific implementation, 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 an 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 then output it to the load F.

[0050] In specific implementation, the switching power supply 100 can be used to realize AC 165-275V input and DC 24V or DC48V output, and provide a DC power supply (e.g., DC24V) for the load F. It should be noted that the switching power supply 100 is a power supply with mature prior art and has been widely used, for example, it can be a switching power supply module of model MW1-Z24 / 60 produced by Tianjin Railway Signal Co., Ltd., which can realize AC 165-275V input and DC 24V output.

[0051] In the present invention, in a specific implementation, the operational amplifier U1 is an electrical component that is mature in the prior art and has been widely used. For example, it can be an operational amplifier of model LM258 produced by Texas Instruments (TI) or STMicroelectronics (ST). It is a general operational amplifier that can amplify the error signal.

[0052] It should be noted that, for the operational amplifier U1, the first pin is the inverting input terminal. For the inverting input terminal, the polarity of the input signal change at this terminal is opposite to that at the output terminal. The second pin is the non-inverting input terminal. 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. The third pin is the operational output terminal. The 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 the 1st and 2nd pins of the operational amplifier U1 are connected to the resistors R1 and R2 respectively, so as to collect the voltage difference signal across the sampling resistor Rsense. The resistor R3 connected between the 2nd and 3rd pins of the operational amplifier U1 constitutes the feedback amplification loop of the operational amplifier, which is used to amplify the voltage difference signal across the sampling resistor Rsense. The 3rd pin of the operational amplifier U1 is connected to the 1st pin of the optocoupler U2, that is, connected to the anode of the light-emitting diode in the optocoupler U2. When the voltage signal of the 3rd pin of the operational amplifier U1 changes, the light intensity of the light-emitting diode inside the optocoupler U2 changes accordingly. Therefore, when the voltage difference across the sampling resistor Rsense changes, the light intensity of the light-emitting diode of the optocoupler 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 light-emitting diode of the optocoupler U2. Conversely, the opposite is true.

[0054] In the present invention, in a specific implementation, the optocoupler U2 is an electrical component that is mature in the prior art and has been widely used. For example, the optocoupler U2 can be an optocoupler product of model EL817 produced by Everlight Electronics Industry Co., Ltd., or a general optocoupler product produced by other companies. In the circuit of the present invention, it is used to isolate the output voltage signal of the operational amplifier U1 and convert the change of the input voltage into the change of the output impedance of the phototransistor in the optocoupler.

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

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

[0057] In the present 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 will be generated across the sampling resistor Rsense. The resistors R1, R2, R3 and the operational amplifier U1 constitute a typical differential amplifier circuit, which can amplify the voltage difference generated across the sampling resistor Rsense so as to drive the light-emitting diode in the optocoupler U2 to emit light. 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 internal oscillator of the PWM controller and determine the output drive frequency of the PWM controller.

[0058] In the present invention, in specific implementation, the sampling resistor Rsense, the resistor R1, the resistor R2, the resistor R3, the resistor R4, the timing resistor Rt and the timing capacitor Ct are all conventional components. The selection of the specific values ​​of these resistors and capacitors is related to the output power of the specific power supply. Generally, the sampling resistor Rsense has a value ranging from a few milliohms to hundreds of milliohms, and is selected according to the rated current of the load, so that the power loss generated on the sampling resistor Rsense is as small as possible, and at the same time, the voltage signal output by the operational amplifier U1 is sufficient to drive the light-emitting diode of the optical coupler U2, so that the current signal flowing through the light-emitting diode is within the range of 1mA-10mA.

[0059] In specific implementation, taking a switching power supply with a rated output current of 10A as an example, the value of the sampling resistor Rsense can be set to 10mΩ, the resistors R1 and R2 are both 10kΩ, the resistor R3 is 100kΩ, and the resistor R4 is 100Ω. Then, when the power supply outputs a current of 10A, the voltage difference U=I*R=0.1V generated across the sampling resistor Rsense, the output voltage of the operational amplifier U1 is up to 1V, and the maximum current flowing through the light-emitting diode in the optocoupler U2 through the current-limiting resistor R4 does not exceed 10mA. When the output current of the power module (i.e., the switching power supply 100) changes in the range of 0-10A, the current of the light-emitting diode in the optocoupler U2 changes in the range of 0-10mA. Of course, according to the different rated currents of different switching power supplies, different resistance values ​​can also be selected to sample the output current, and finally the current flowing through the light-emitting diode in the optocoupler is controlled to change in the range of 0-10mA.

[0060] In the present invention, in a specific implementation, the output terminal OUT of the PWM controller is connected to the switch tube Q1 (which is the original switch tube in the switching power supply 100) through the driving resistor R5.

[0061] It should be noted that the switch tube Q1 is an original switch tube in the switching power supply 100, which is used to control the on and off of the main circuit (ie, the output loop) of the switching power supply 100 to achieve power conversion of the power supply.

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

[0063] The other end of the driving resistor R5 is connected to the gate G of the switch tube Q1 .

[0064] It should be noted that the PWM controller outputs a PWM drive signal, see Figure 1 As shown, the OUT terminal (i.e., output pin) of the PWM controller is used to output a driving signal, which is generally connected to the driving pole of the driven switch tube through a driving resistor R5. Figure 1As shown, the output terminal OUT of the driver (ie, the PWM controller) is connected to the driving pole of the switch tube Q1, ie, the gate (Gate) of the MOSFET or IGBT, through the driving resistor R5.

[0065] It should be noted that the switch tube Q1 can be a common MOSFET or IGBT. Taking MOSFET as an example, the switch tube model can be the commonly used MOSFET model FQP4N90C of ON Semiconductor (onsemi) or the MOSFET model STFW3N150 of STMicroelectronics (ST). The switch tube Q1 in the switching power supply is used to realize the conduction and shutdown of the main circuit and realize the power conversion of the power supply.

[0066] Among them, it should be noted that MOSFET (metal-oxide-semiconductor field-effect transistor) is a key electronic component widely used in electronic devices, especially playing an important role in the fields of power management and power conversion.

[0067] exist Figure 1 In the figure, the switch tube Q1 is a MOSFET, and the switch tube Q1 has 3 pins, the first pin is the gate G, the second pin is the drain D, and the third pin is the source S. Gate (Gate, G): The gate is the key pin that controls the on or off of the MOSFET, and controls the current between the source and the drain through the electric field effect. Source (Source, S): The source is a main endpoint for current outflow. Drain (Drain, D): The drain is another main endpoint for current inflow or outflow, opposite to the source.

[0068] exist Figure 1 In the embodiment, one end of the driving resistor R5 is connected to the output terminal OUT of the PWM controller, and the other end of the driving resistor R5 is connected to the first pin (gate) of the switch tube Q1; the second pin and the third pin of the switch tube Q1 are connected to other positions of the main circuit of the switching power supply, for example: the second pin of the switch tube Q1 can be connected to energy storage elements such as a transformer or an inductor, and the third pin of the switch tube Q1 can be connected to the ground. According to the topological structure of the specific switching power supply, the second pin and the third pin of different switching tubes can have different connection methods. It should be noted that the specific connection method of the switch tube in the switching power supply is common knowledge in the existing switching power supply and will not be repeated here.

[0069] In the present invention, in specific implementation, the PWM controller is a universal controller, which is widely used as a control chip of a switching power supply, and its main function is to control the on and off of the switch tube by adjusting the pulse width, thereby achieving precise power control. There are many common manufacturers and models of PWM controllers, for example, common manufacturers and models can be: TL494, UC3846, LM3409 and other models of Texas Instruments (TI); NCP1252, NCP1034 and other models of ON Semiconductor (onsemi).

[0070] It should be noted that the pins of the PWM controller vary greatly depending on the specific model of the controller. In the present invention, the PWM controller pins used are mainly RT, CT, and OUT pins, wherein the RT pin is a timing resistor pin, which is a resistor terminal for setting the oscillator frequency; the CT pin is a timing capacitor pin, which is a capacitor terminal for setting the oscillator frequency; and the OUT pin is a PWM drive signal output pin, which is used to output a drive signal with a pulse width variation generated by the PWM controller to drive the switch tube on and off. The device parameters of the RT pin and the CT pin of the PWM controller determine the switching frequency of the OUT output pin.

[0071] In specific implementation, when the PWM controller adopts the UC3846 chip as exemplified above, in the chip with a 16-pin package structure, the 8th pin is the defined CT pin, the 9th pin is the defined RT pin, and the 11th pin 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, where the RT pin is the timing resistor pin, which is the resistor terminal used to set the oscillator frequency; the CT pin is the timing capacitor pin, which is the capacitor terminal used to set the oscillator frequency; the OUT pin is the PWM drive signal output pin, which is used to output the drive signal with pulse width variation generated by the PWM controller to drive the switch tube 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 the present invention, in specific implementation, the only pin associated with the voltage stabilizing circuit of the present invention is the RT pin. The 4th pin of the optocoupler U2 is connected to the RT pin of the PWM controller, and the 3rd pin of the optocoupler U2 is connected to the ground (i.e., signal ground) of the PWM controller.

[0073] It should be noted that, for the pulse frequency modulation voltage stabilization circuit provided by the present invention, the output voltage of the circuit can be different voltage specifications such as DC 12V, 24V, 48V, etc.

[0074] Based on the voltage stabilizing circuit provided by the present invention, the present invention further provides a switching power supply, which includes the voltage stabilizing circuit as described above.

[0075] In the present invention, in a specific implementation, for the switching power supply provided by the present invention, the PWM controller in the voltage stabilizing circuit is connected to the switch tube Q1 (specifically, the original switch tube in the switching power supply).

[0076] In a specific implementation, the output terminal OUT of the PWM controller is connected to the switch tube Q1 through the driving resistor R5.

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

[0078] The other end of the driving resistor R5 is connected to the gate G (first pin) of the switch tube Q1.

[0079] It should be noted that the drive signal output pin OUT of the PWM controller outputs a drive signal with a varying pulse width, which is used to drive the on and off of the original switch tube in the switching power supply. 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 the first pin (i.e., the gate) of the switch tube 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 original switching power supply circuit. The drive signal output from the OUT pin of the PWM controller passes through the drive resistor R5, and the resistor R5 limits the current of the drive signal to prevent the drive signal amplitude from being too high and damaging the switch tube Q1.

[0080] In terms of specific implementation, it should be noted that the switching power supply of the present invention can be basically the same as the switching power supply module of model MW1-Z24 / 60 produced by Tianjin Railway Signal Co., Ltd., except that: a new design is added as follows Figure 1 The voltage regulator circuit shown.

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

[0082] It should be noted that, for a switching power supply, the switch tube Q1 can be a common MOSFET or IGBT. Taking MOSFET as an example, the switch tube model can be the commonly used MOSFET model FQP4N90C of ON Semiconductor (onsemi), or the MOSFET model STFW3N150 of STMicroelectronics (ST). The switch tube Q1 in the switching power supply is used to realize the conduction and shutdown of the main circuit and realize the power conversion of the power supply.

[0083] In order to more clearly understand the technical solution of the present invention, the working principle of the present invention is explained below.

[0084] The values ​​of the timing resistor Rt and the timing capacitor Ct connected to the PWM controller determine the clock output frequency of the oscillator inside the PWM controller, and the clock output frequency determines the switching frequency of the switch tube in the switching power supply. The oscillator inside the PWM controller is an RC oscillator. The larger the product of the resistance value of the timing resistor Rt and the capacitance value of the timing capacitor Ct, the smaller the clock frequency of the RC oscillator and the output switching frequency; conversely, the smaller the product of the resistance value of the timing resistor Rt and the capacitance value of the timing capacitor Ct, the larger the clock frequency of the RC oscillator and the output switching frequency.

[0085] When the output current of the switching power supply 100 increases (i.e., the power current required by the load F), the equivalent resistance between the 3rd and 4th pins of the optocoupler U2 decreases. Therefore, the total resistance of the equivalent resistance 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 switch tube) increases accordingly.

[0086] When the output current of the switching power supply 100 (i.e., the power current required by the load F) becomes smaller (for example, when unloaded), the equivalent resistance between the 3rd pin and the 4th pin of the optocoupler U2 becomes larger. Therefore, the total resistance of the equivalent resistance connected in parallel with the timing resistor Rt becomes larger, the output clock frequency of the RC oscillator becomes smaller, and the output drive frequency (i.e., the drive frequency output by the PWM controller to the switch tube) becomes larger accordingly.

[0087] In summary, based on the technical solution of the present invention, a sampling resistor for the DC output current is adopted, which can realize a pulse frequency modulation (PFM) control method on the basis of a general PWM controller, thereby exerting the technical effect of the existing pulse frequency modulation (PFM) control method, that is, the driving frequency provided by the PWM controller to the switching tube can be automatically adjusted. The larger the load, the higher the driving frequency. When the load is not loaded, the driving frequency is reduced, which can significantly reduce the no-load loss.

[0088] Compared with the prior art, the voltage stabilizing circuit provided by the present invention has the following beneficial effects:

[0089] 1. The present invention can automatically adjust the driving frequency of the switch tube according to load changes, and can improve the EMI (electromagnetic interference) characteristics of the switching power supply;

[0090] 2. The voltage stabilizing circuit of the present invention, as a new type of pulse frequency modulation voltage stabilizing circuit, can be widely used in various types of controllers. The control method of pulse frequency adjustment can reduce the switching frequency of the switching tube, extend the service life of the power device, and bring good economic and social benefits.

[0091] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A voltage stabilizing circuit, characterized in that: include: Sampling circuit, optocoupler U2, timing resistor Rt, timing capacitor Ct and PWM controller; Wherein, the sampling circuit includes a sampling resistor Rsense, a resistor R1, a resistor R2, a resistor R3 and an 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 the resistor R1 is connected to the inverting input end of the operational amplifier U1 and one end of the resistor R3 respectively; The other end of the resistor R2 is connected to the non-inverting input terminal of the operational amplifier U1; The output end of the operational amplifier U1 is connected to the other end of the resistor R3 and one end of the resistor R4 respectively; The other end of the resistor R4 is connected to the first pin of the optocoupler U2; The second pin of the optocoupler U2 is grounded; The third pin of the optocoupler U2 is connected to the signal ground of the PWM controller and one end of the timing resistor Rt respectively; The 4th pin of the 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 stabilizing circuit according to 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 stabilizing circuit according to claim 1, characterized in that: The sampling resistor Rsense is arranged on a connection line between a voltage output terminal of the switching power supply (100) and a voltage input terminal of a load F.

4. The voltage stabilizing circuit according to claim 3, characterized in that: The voltage output terminal Vout of the switching power supply comprises a positive output terminal L+ and a negative output terminal L- on the switching power supply (100); The voltage input terminal of the load F includes a positive input terminal DC+ and a 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 a connection line between a positive output terminal L+ on a switching power supply (100) and a positive input terminal DC+ on a load F; The negative output terminal L- of the switching power supply (100) is connected to the negative input terminal DC- of the load F.

5. The voltage stabilizing circuit according to any one of claims 2 to 4, characterized in that: The second pin of the optocoupler U2 is connected to the signal ground of the switching power supply (100).

6. The voltage stabilizing circuit according to any one of claims 2 to 4, characterized in that: The output terminal OUT of the PWM controller is connected to the original switch tube Q1 in the switch power supply (100) through the driving resistor R5.

7. A switching power supply, characterized in that: The invention comprises the voltage stabilizing circuit as claimed in claims 1 to 6.

8. The switching power supply according to claim 7, characterized in that: The PWM controller in the voltage stabilizing circuit is connected to the switch tube Q1.

9. The switching power supply according to claim 8, characterized in that: The output terminal OUT of the PWM controller is connected to the switch tube Q1 through the driving resistor R5.

10. The switching power supply according to claim 9, characterized in that: The output terminal OUT of the PWM controller is connected to one end of the driving resistor R5; The other end of the driving resistor R5 is connected to the gate G of the switch tube Q1 .

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