CN102403697B - A kind of Switching Power Supply over-voltage over-current protection circuit and guard method - Google Patents

Abstract

The invention is applicable to the technical field of switching power supply products, and provides a switching power supply overvoltage and overcurrent protection circuit and protection method. The voltage after rectification of the auxiliary winding of the switching transformer is detected in real time through the overvoltage detection circuit. When the voltage value output by the switching transformer is normal , supply power to the power control chip through the series voltage regulator circuit, when the output voltage of the power system rises beyond the safe range, the voltage regulator tube in the overvoltage detection circuit is reversely broken down, triggering the overvoltage protection function of the power control chip, the power supply The control chip stops working, so that the power supply system can be effectively protected. Since the overvoltage detection circuit of the present invention detects the rectified voltage of the auxiliary winding of the switching transformer, it solves the problems of complex circuits, slow protection response speed, and reliability in the prior art. No high problem, the circuit structure is simple, low cost, and has broad market prospects.

Description

A switching power supply overvoltage and overcurrent protection circuit and protection method

technical field

The invention belongs to the technical field of switching power supply products, and in particular relates to a switching power supply overvoltage and overcurrent protection circuit and a protection method.

Background technique

With the rapid development of science and technology, various electrical products are used in households and public places. Due to the substantial increase in electricity consumption, overvoltage and overcurrent phenomena often occur in the mains power supply, which directly leads to excessive voltage of electrical products. Excessive current can easily damage electrical products.

With the development of TV products, the requirements for standby power consumption are becoming more and more stringent. Therefore, the standby step-down circuit with the function of reducing standby power consumption has been widely used. The overvoltage protection function is one of the indispensable protection functions of switching power supply products. The design of overvoltage protection circuit is a very important design in the development process of switching power supply. The existing overvoltage protection design method is usually to connect an overvoltage detection circuit 500 at the secondary output terminal of the isolation transformer, and take Overvoltage signal, circuit principle block diagram and circuit diagram as shown in Figures 1 and 2, the circuit includes a power control chip 100, a transformer 200, a series voltage regulator circuit 300, a half-wave rectifier circuit 400, using the circuit shown in the figure When the power supply is in standby and full-load operation, since the VCC voltage of the auxiliary winding of the transformer is very different, a series voltage stabilizing circuit 300 is needed to stabilize the rectified and filtered voltage of the auxiliary winding to supply power to the power control chip 100, but a series voltage stabilizing circuit is added After the circuit, the overvoltage protection function of the internal VCC of the power supply control chip 100 cannot be directly triggered, and an external overvoltage detection circuit 500 is required, and an optocoupler N2 is used as a control device to pull down the voltage of the VCC pin of the power supply control chip 100, thereby triggering the power supply. The protection function of the control chip, the optocoupler is a safety component between the jumper and the hot and cold ground, the design of this overvoltage protection circuit is complex, there are many components, the reliability is also reduced, and the cost is high.

Therefore, there are deficiencies in the prior art and need to be improved and improved.

Contents of the invention

The object of the present invention is to provide an overvoltage protection circuit and an overvoltage protection method for a switching power supply, which solve the problems of complex circuits, low reliability and high cost in the prior art.

The present invention is achieved in this way. A switching power supply overvoltage and overcurrent protection circuit includes a power supply control chip, a switching transformer and a series voltage stabilizing circuit. The voltage stabilizing circuit is connected to the power supply control chip and is the Provide power supply voltage, the power supply control chip controls the switching transformer, and it is characterized in that it also includes an overvoltage detection circuit and a half-wave rectification filter circuit, and the auxiliary winding of the switch transformer is connected to the input end of the half-wave rectification filter circuit , the signal output end of the half-wave rectification filter circuit is connected in parallel with the overvoltage detection circuit and the series voltage stabilization circuit, and the overvoltage detection circuit and the voltage stabilization circuit are respectively connected to the power supply end of the power control chip, When the power system is normal, the voltage value output by the switching transformer is normal, and the series voltage regulator circuit supplies power to the power control chip. When the power system is abnormally overvoltage, the overvoltage detection circuit works and The signal is directly provided to the power terminal of the power control chip, thereby triggering the built-in overvoltage protection function of the power control chip, making the power control chip stop working, and realizing the power output protection of the external circuit.

Wherein, the overvoltage detection circuit includes a voltage regulator tube ZD4, a voltage regulator tube ZD2, and a diode D2. The positive pole is connected to the positive pole of the diode D2, the negative pole of the diode D2 is respectively connected to the negative pole of the voltage regulator transistor ZD2 and connected to the power supply pin VCC terminal of the power control chip, and the positive pole of the voltage regulator transistor ZD2 is grounded, so The voltage regulator tube ZD4, the diode D2 and the voltage regulator tube ZD2 form an overvoltage breakdown current loop, which is used for reverse breakdown of the voltage regulator tube ZD4 when the power supply system is overvoltage, so that the power supply control The voltage of the power supply pin VCC of the chip reaches the regulated voltage value of the regulator tube ZD2, triggering the protection function of the power supply chip.

Wherein, the overvoltage detection circuit further includes a diode D1, the diode D1 is connected in parallel with the diode D2, the cathode of the diode D1 is connected to the power supply pin VCC terminal of the power control chip, and the anode of the diode D1 Connect the signal output terminal of the series voltage stabilizing circuit, the diode D1 and the diode D2 are used to prevent the power supply control chip at the moment of startup, and the high voltage at the VCC terminal of the chip will flow back to the series voltage stabilizing circuit and the in a half-wave rectifier circuit.

Wherein, the anode of the diode D1 is connected to the emitter stage of the triode Q2 in the series voltage stabilizing circuit, the base stage of the triode Q2 is grounded through the voltage stabilizing transistor ZD3 in the series voltage stabilizing circuit, and the triode Q2 The collector is connected in series with the resistor R5 and then connected to the cathode of the diode D6 of the half-wave rectification circuit, and the anode of the diode D6 is connected to the auxiliary winding of the switching transformer through the resistor R4.

A method for overvoltage and overcurrent protection of a switching power supply, characterized in that the method comprises the steps of:

A. The overvoltage detection circuit detects the rectified voltage of the auxiliary winding of the switching transformer in real time;

B. If the voltage value output by the switching transformer is normal, supply power to the power input terminal of the power control chip through the series voltage regulator circuit, and the power control chip works normally;

C. When the output voltage or current of the power system increases, the voltage of the auxiliary winding of the switching transformer after rectification also increases, and when the output voltage rises beyond the safe range, the regulator tube ZD4 in the overvoltage detection circuit is reversed. To breakdown, Zener tube ZD4, diode D2 and Zener tube ZD2 form an overvoltage breakdown current loop, so that the voltage of the power supply pin VCC of the power control chip reaches the voltage regulation value of the second voltage regulator tube , thus triggering the overvoltage protection function of the power chip.

Wherein, the overvoltage detection circuit further includes a diode D1, the diode D1 is connected in parallel with the diode D2, and the diode D1 and the diode D2 are used to prevent the power supply control chip from The instantaneous high voltage at the end flows back into the series voltage stabilizing circuit and the half-wave rectifying circuit.

The beneficial effects of the present invention are: the switching power supply overvoltage and overcurrent protection circuit and method provided by the present invention, when the output voltage or current of the power supply system increases, the voltage after rectification of the auxiliary winding of the transformer also increases accordingly, so that The voltage regulator ZD4 in the overvoltage detection circuit is reversely broken down, so that the voltage of the power supply pin VCC of the power supply control chip reaches the voltage regulation value of the voltage regulator ZD2, thereby triggering the overvoltage protection function of the power chip, so that the power system Effective protection can be obtained, the circuit protection responds quickly, the circuit is simple, the cost is low, the reliability is high, and the circuit has broad market prospects.

Description of drawings

Fig. 1 is a prior art circuit principle block diagram;

Fig. 2 is a prior art circuit schematic diagram;

Fig. 3 is a schematic block diagram of the circuit of the present invention;

Fig. 4 is a schematic circuit diagram of the present invention.

detailed description

In order to solve the problems of complex circuits, low reliability and high cost in the current technology, the present invention provides a switching power supply overvoltage and overcurrent protection circuit and protection method. The rectified voltage of the winding, when the output voltage value of the switching transformer is normal, supplies power to the power control chip through the series voltage regulator circuit, and the power control chip is equivalent to an electronic switch. When the system power supply is normal, a voltage of 12V is generated on the secondary side of the switching transformer Used for external equipment; when the output voltage or current of the power system increases, the voltage of the auxiliary winding of the switching transformer also increases after rectification. wear, trigger the overvoltage protection function of the power supply chip, the power supply control chip stops working, so that the power supply system can be effectively protected, because the overvoltage detection circuit of the present invention detects the voltage after the auxiliary winding of the switching transformer is rectified, it solves the problem of the prior art An overvoltage detection circuit is connected to the secondary output terminal of the isolation transformer, so that the response speed of the circuit protection is slow and the reliability is not high.

In order to make the object, technical solution and advantages of the present invention more clear and definite, the present invention will be further described in detail below with reference to the accompanying drawings and examples.

Accompanying drawing 3 is the schematic block diagram of circuit of the present invention, comprises power supply control chip 100, switching transformer 200, series voltage regulator circuit 300, half-wave rectification filter circuit 400 and overvoltage detection circuit 500, wherein voltage regulator circuit 300 and power supply control chip 100 connected to provide power supply voltage for the power control chip, the power control chip 100 is connected to the switching transformer 200, the power control chip 100 is equivalent to an electronic switch, and the auxiliary winding of the switching transformer (as shown in Figure 4, the auxiliary winding of the switching transformer is 4, 6 terminals , the main winding is the two ends of 1 and 2, and the secondary winding is the right side in the figure, which provides 12V power supply) is connected to the input end of the half-wave rectification filter circuit 400, and the signal output end of the half-wave rectification filter circuit 400 is connected in parallel to the overvoltage detection The circuit 500 and the series voltage stabilizing circuit 300, the overvoltage detection circuit 500 and the voltage stabilizing circuit 300 are respectively connected to the power terminal of the power control chip. The voltage circuit 300 directly supplies power to the power control chip 100; when the power system is abnormally overvoltage or overcurrent, the overvoltage detection circuit starts to work, and directly provides the overvoltage signal to the power terminal of the power control chip 100, thereby triggering the power control The built-in overvoltage protection function of the chip makes the power control chip 100 stop working (equivalent to a closed state), and realizes the power output protection of external circuits, such as external TVs, computers and other equipment. The power system here includes external power supply, load line Wait.

Accompanying drawing 4 is the schematic diagram of the circuit of the present invention, each component and parts is explained in more detail below according to the schematic diagram, in the circuit diagram power control chip 100 is IC chip, has 6 pins, including pin 1 is Drain pin , through a fuse L1 connected to the 2 terminals of the switching transformer (2 terminals as the main winding), pin 2 is the GND pin grounding, pin 3 is the VCC power input terminal of the chip, pin 4 is the FB feedback pin, pin Pin 5 is the YNC synchronous pin, and pin 6 is the VST high-voltage start pin.

The left side of the switching transformer 200 includes the main winding (primary side) 1, 2 terminals are connected to the external power supply, 4 and 6 terminals are auxiliary windings, the 4 terminal is connected to one end of the resistor R4 in the half-wave rectification filter circuit 400, and the 6 terminal is grounded, and the right side of the switching transformer 200 Including the secondary winding, providing 12V voltage to the external TV; the series voltage stabilizing circuit 300 mainly includes a resistor R5, a three-stage tube Q2 and a voltage stabilizing tube ZD3, wherein one end of the resistor R5 is respectively connected to the diode D6 in the half-wave rectification filter circuit 400 The negative electrode and capacitors C7, C8, the capacitors C7 and C8 are connected in parallel and grounded at the same time, the other end of the resistor R5 is connected to the collector of the triode Q2, the base of the triode Q2 is grounded through the voltage regulator ZD3, and the emitter of the triode Q2 Connect the anode of the diode D1 in the overvoltage detection circuit 500; the overvoltage detection circuit 500 of the present invention includes a voltage regulator tube ZD4, a voltage regulator tube ZD2, a diode D2 and a diode D1, and the negative pole of the voltage regulator tube ZD4 is connected to a half-wave rectification filter circuit The signal output terminals of the half-wave rectification and filtering circuit 400 are respectively connected to the negative pole of the diode D6, one end of the capacitor C7 and C8), the positive pole of the Zener diode ZD4 is connected to the positive pole of the diode D2, and the negative pole of the diode D2 is respectively connected to the Zener tube The negative pole of ZD2 is connected to the power supply pin VCC of the power control chip (3-terminal pin), the positive pole of the Zener tube ZD2 is grounded, the Zener tube ZD4, the diode D2 and the Zener tube ZD2 form an overvoltage breakdown current loop, When the power supply system is overvoltage, the rectified voltage of the auxiliary winding of the transformer will also increase (that is, the voltage after passing through the half-wave rectification and filtering circuit will increase), so that the excessive voltage will make the first regulator tube ZD4 is reversely punctured, and the current passes through the overvoltage breakdown current loop formed above, so that the voltage of the power pin VCC of the power control chip reaches the voltage regulation value of the second voltage regulator tube ZD2, triggering the overvoltage protection function of the power chip , so that the power chip stops supplying power; similarly, when the load (that is, the output current) of this circuit changes from small to large, the duty cycle of the voltage waveform at the primary end of the transformer (that is, pins 1 and 2 of the transformer T in the circuit diagram) also changes. Then it will become larger, which will lead to the increase of the voltage after rectification and filtering of the auxiliary winding of the transformer. When the voltage rises to a certain value, it will reverse the voltage regulator ZD4 and trigger the overvoltage of the chip. Overvoltage protection, by adjusting the number of turns of the auxiliary winding of the transformer and the parameters of the Zener tube ZD4, the overcurrent protection point and overvoltage protection point can be flexibly set.

Diode D2 and diode D1 are connected in parallel, the cathode of diode D1 is connected to the power supply pin VCC terminal of the power control chip, the anode of diode D1 is connected to the emitter stage of transistor Q2 in the series regulator circuit, and diode D2 and diode D1 are used to prevent power control At the moment when the chip 100 is started, the VCC terminal of the chip instantly flows high voltage back into the series voltage stabilizing circuit 300 and the half-wave rectifying circuit 400 .

Overvoltage or overcurrent protection method of the present invention, its steps are described as follows:

S100. The overvoltage detection circuit detects the rectified voltage of the auxiliary winding of the switching transformer in real time;

S200. When the voltage value output by the switching transformer is normal, supply power to the power input end of the power control chip through the series voltage stabilizing circuit, and the power control chip works normally;

S300. When the output voltage or current of the power supply system increases, the voltage after rectification of the auxiliary winding of the switching transformer also increases accordingly, and when the output voltage rises beyond the safe range, the first regulator tube in the overvoltage detection circuit is reversed Breakdown, the voltage regulator tube ZD4, diode D2 and voltage regulator tube ZD2 form an overvoltage breakdown current loop, and the overvoltage signal is directly provided to the power supply terminal of the power control chip. Due to the function of the voltage regulator tube ZD2, the power control chip The voltage of the power supply pin VCC reaches the regulated value of the regulator tube ZD2, thereby triggering the built-in overvoltage protection function of the power control chip, making the power control chip stop working, and realizing the power output protection of the external circuit.

Among them, when the power system is overvoltage, the rectified voltage of the auxiliary winding of the transformer will increase accordingly, and when the load (that is, the output current) carried changes from small to large, it will also cause the rectified and filtered voltage of the auxiliary winding of the transformer raised.

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present invention should be included in the protection of the present invention. within range.

Claims (5)

1. a Switching Power Supply over-voltage over-current protection circuit, comprise power supply control chip, switch transformer and serial regulating circuit, described serial regulating circuit is connected with described power supply control chip, for described power supply control chip provides supply voltage, switch transformer described in described power supply control chip control, it is characterized in that, also comprise over-voltage detection circuit and halfwave rectifier filter circuit, the auxiliary winding of described switch transformer is connected with the input of described halfwave rectifier filter circuit, the signal output part of described halfwave rectifier filter circuit be connected in parallel described over-voltage detection circuit and described serial regulating circuit, described over-voltage detection circuit is connected respectively described power supply control chip power end with described mu balanced circuit, in the time that power-supply system is normal, the magnitude of voltage of described switch transformer output is normal, described serial regulating circuit is given described power supply control chip power supply, when described power-supply system overvoltage, described over-voltage detection circuit work also directly offers described power supply control chip power end by overvoltage signal, thereby trigger the built-in over-voltage protecting function of described power supply control chip, described power supply control chip is quit work, realize the power supply output protection to external circuits,

Described over-voltage detection circuit comprises voltage-stabiliser tube ZD4, voltage-stabiliser tube ZD2 and diode D2, the negative pole of described voltage-stabiliser tube ZD4 connects the signal output part of described halfwave rectifier filter circuit, the positive pole of described voltage-stabiliser tube ZD4 connects the positive pole of described diode D2, the negative pole of described diode D2 connects respectively the negative pole of described voltage-stabiliser tube ZD2 and connects the power pins VCC end of described power supply control chip, the plus earth of described voltage-stabiliser tube ZD2, described voltage-stabiliser tube ZD4, diode D2 and voltage-stabiliser tube ZD2 form an over-voltage breakdown current loop, for in the time of described power-supply system overvoltage, described voltage-stabiliser tube ZD4 is reversed and punctures, make the voltage of the power pins VCC of described power supply control chip reach the voltage stabilizing value of described voltage-stabiliser tube ZD2, trigger the defencive function of described power supply chip.

2. Switching Power Supply over-voltage over-current protection circuit according to claim 1, it is characterized in that, described over-voltage detection circuit also comprises diode D1, described diode D1 and described diode D2 are connected in parallel, the negative pole of described diode D1 connects the power pins VCC end of described power supply control chip, the positive pole of described diode D1 connects described serial regulating circuit signal output part, described diode D1 and described diode D2 are used for preventing that described power supply control chip from starting moment, described chip VCC end instantaneous pressure is back in described serial regulating circuit and described half-wave rectifying circuit.

3. Switching Power Supply over-voltage over-current protection circuit according to claim 2; it is characterized in that; the positive pole of described diode D1 connects the emitting stage of the triode Q2 in described serial regulating circuit; the ground level of described triode Q2 is by the voltage-stabiliser tube ZD3 ground connection in described serial regulating circuit; the colelctor electrode of described triode Q2 connects the negative pole of the diode D6 of described half-wave rectifying circuit after connecting with resistance R 5, the positive pole of described diode D6 is connected to the auxiliary winding of described switch transformer by resistance R 4.

4. a Switching Power Supply over-voltage over-current protection method, is characterized in that, described method comprises the steps:

Voltage after A, the auxiliary winding rectification of the real-time sense switch transformer of over-voltage detection circuit;

If the magnitude of voltage of the described switch transformer output of B is normal, the power input power supply by serial regulating circuit to power supply control chip, described power supply control chip is normally worked;

C, raise when power-supply system output voltage or electric current, after the auxiliary winding rectification of described switch transformer, voltage also increases, output voltage raises while exceeding safe range, voltage-stabiliser tube ZD4 in described over-voltage detection circuit is reversed and punctures, voltage-stabiliser tube ZD4, diode D2 and voltage-stabiliser tube ZD2 form an over-voltage breakdown current loop, make the voltage of the power pins VCC of described power supply control chip reach the voltage stabilizing value of the second voltage-stabiliser tube, thereby trigger the over-voltage protecting function of power supply chip;

Described over-voltage detection circuit comprises voltage-stabiliser tube ZD4, voltage-stabiliser tube ZD2 and diode D2, the negative pole of described voltage-stabiliser tube ZD4 connects the signal output part of halfwave rectifier filter circuit, the positive pole of described voltage-stabiliser tube ZD4 connects the positive pole of described diode D2, the negative pole of described diode D2 connects respectively the negative pole of described voltage-stabiliser tube ZD2 and connects the power pins VCC end of described power supply control chip, the plus earth of described voltage-stabiliser tube ZD2, described voltage-stabiliser tube ZD4, diode D2 and voltage-stabiliser tube ZD2 form an over-voltage breakdown current loop, for in the time of described power-supply system overvoltage, described voltage-stabiliser tube ZD4 is reversed and punctures, make the voltage of the power pins VCC of described power supply control chip reach the voltage stabilizing value of described voltage-stabiliser tube ZD2, trigger the defencive function of described power supply chip.

5. Switching Power Supply over-voltage over-current protection method according to claim 4; it is characterized in that; described over-voltage detection circuit also comprises diode D1; described diode D1 and described diode D2 are connected in parallel; described diode D1 and described diode D2 are used for preventing that described power supply control chip from starting moment, and described chip VCC end instantaneous pressure is back in described serial regulating circuit and half-wave rectifying circuit.