CN103944147B - A kind of protective circuit of switch power source and its control method - Google Patents

Abstract

A switching power supply protection circuit and its control method according to the present invention, comprising an input filter circuit, a power conversion circuit, a high-frequency transformer, an output rectifier circuit, an output filter circuit, a drive control circuit, an output feedback control circuit, and an overcurrent protection circuit , the output filter circuit includes an output filter inductor, and the overcurrent protection circuit includes a current conditioning circuit and an output current sampling circuit. In the switching power supply protection circuit described in the present invention, an output current sampling circuit and a current conditioning circuit are added in the circuit, and the sampling circuit can achieve almost no power loss, which creates certain conditions for improving power supply efficiency, and not only improves switching The output efficiency of the power supply reduces the line loss of the circuit and has strong anti-interference ability.

Description

A switching power supply protection circuit and its control method

technical field

The invention relates to the field of switching power supply circuits, in particular to a switching power supply protection circuit and a control method thereof.

Background technique

The switching power supply protection circuit is an important part of the switching power supply system. Its function is to protect the power components in the switching power supply and other circuits in the system to work in a safe area when the switching power supply is in the process of system debugging or use. The switching power supply overcurrent protection circuit is one of the core units of the switching power supply protection circuit. When the load on the output terminal of the power supply exceeds the rated load, it will cause damage to the power supply. The overcurrent protection circuit can effectively ensure that the power components of the switching power supply system and the system power supply circuit work in a safe area.

There are many forms of overcurrent protection, which can be mainly divided into two categories: one is cut-off overcurrent protection, and the other is automatic recovery overcurrent protection. In some applications and designs, the cut-off overcurrent protection method is adopted, so that the reliability of the power supply is improved, but it needs to be reset manually after each overcurrent occurs, which is inconvenient for users. Therefore, the automatic recovery type is generally used more. At present, the automatic recovery type overcurrent protection mainly adopts the rated current drooping type overcurrent protection circuit. The overcurrent protection circuit mainly connects the sampling resistor in the output current loop, and then processes the current sampling signal with the overcurrent signal. The disadvantage of this current protection circuit is mainly the existence of the sampling resistor, which reduces the efficiency of the power supply, especially in the case of high current output, the power consumption of the resistor will increase significantly. Therefore, considering the power consumption, the connection of the sampling resistor should be avoided as much as possible.

Contents of the invention

The technical problem to be solved by the present invention is to provide a switching power supply protection circuit and its control method, which changes the structure of the original overcurrent protection circuit. This circuit not only improves the output efficiency of the switching power supply, reduces the line loss of the circuit, but also Strong interference ability.

In order to solve the problems of the technologies described above, the present invention adopts the following technical solutions:

A switching power supply protection circuit, including an input filter circuit, a power conversion circuit, a high-frequency transformer, an output rectifier circuit, an output filter circuit, a drive control circuit, an output feedback control circuit, and an overcurrent protection circuit. The output filter circuit includes an output filter circuit An inductor, the overcurrent protection circuit includes a current conditioning circuit and an output current sampling circuit; the input filter circuit is respectively connected to the output end of the drive control circuit and the input end of the high frequency transformer via the power conversion circuit; The input end of the drive control circuit is connected to the output end of the input filter circuit and the output end of the output feedback control circuit; the output end of the high frequency transformer is connected to the power load via the output rectifier circuit, output filter circuit connected; the output end of the output filter circuit is connected to the input end of the output current sampling circuit, the input end of the output feedback control circuit is connected to the output end of the current conditioning circuit and the output end of the output filter circuit, and the current conditioning circuit The input terminal is connected with the output terminal of the output current sampling circuit.

The output current sampling circuit is composed of a sampling coil and a resistor. The sampling coil and the output filter inductor are wound on the same magnetic core. The end of the sampling coil with the same name is connected with the end of the output filter inductor. The end is connected to the opposite end of the output filter inductor through a resistor.

The current conditioning circuit includes an amplifying circuit composed of an amplifier and a comparison circuit composed of a comparator; the non-inverting input terminal of the amplifier is connected to the opposite end of the sampling coil, and the output terminal of the comparator is connected to the output feedback control circuit .

A switching power supply protection circuit control method, characterized in that, comprising the following steps,

a: The current sampling signal is amplified through the operational amplifier U1;

b: The current sampling signal amplified by the operational amplifier U1 is input to the positive terminal of the comparator U2, and compared with the voltage value of the negative terminal of the comparator U2. When the power supply is working normally, the comparator U2 does not flip; when When the load current reaches the overcurrent protection point, the comparator U2 flips over, and at this time, the output of U2 is high level;

c: Send the output signal of comparator U2 to the feedback comparator U3 in the output feedback control circuit. When U2 outputs a high level, the reference voltage of U3 is pulled down, the output voltage sampling signal is greater than the reference reference voltage, and the feedback comparator U3 outputs Low level, the conduction current of the transistor Q1 increases; when the conduction current of the transistor Q1 reaches 1mA, the pulse width controller of the primary side of the power supply stops outputting the two driving signals of the half-bridge, and pulls down the output voltage.

The beneficial effects of the present invention are: 1. An output current sampling circuit and a current conditioning circuit are added in the circuit, and the sampling circuit can almost achieve no power loss, which creates certain conditions for improving the power supply efficiency, and not only improves the efficiency of the switching power supply. The output efficiency reduces the line loss of the circuit and has strong anti-interference ability. 2. The sampling coil is wound on the output filter inductance, both of which are wound on the same magnetic core, the sampling circuit components are less, and the implementation is more convenient. 3. Working within the temperature range of -55°C to +125°C, it can achieve effective overcurrent protection when the power load exceeds 1.4 times the rated load; the product has high integration and good reliability.

Description of drawings

Fig. 1 is a circuit block diagram of the present invention;

Fig. 2 is the output current sampling circuit of the present invention;

Fig. 3 is the current conditioning circuit of the present invention.

detailed description

The present invention will be further described below in conjunction with the accompanying drawings.

As shown in Figure 1, a switching power supply protection circuit and its control method are composed of an input filter circuit 1, a power conversion circuit 2, a high-frequency transformer 3, an output rectifier circuit 4, an output filter circuit 5, an output feedback control circuit 8, and a drive control circuit. Circuit 7, composed of an overcurrent protection circuit. The overcurrent protection circuit includes a current conditioning circuit 9 and an output current sampling circuit 10; the input filter circuit 1 is connected to the output terminal of the drive control circuit 7 and the input terminal of the high-frequency transformer 3 via the power conversion circuit 2; the input terminal of the drive control circuit 7 The output end of the input filter circuit 1 and the output end of the output feedback control circuit 8 are connected; the output end of the high-frequency transformer is connected with the power supply load 6 through the output rectifier circuit 4 and the output filter circuit 5; the output end of the output filter circuit 5 is connected with the The input terminal of the output current sampling circuit 10 is connected, the input terminal of the output feedback control circuit 8 is connected with the output terminal of the current conditioning circuit 9 and the output terminal of the output filter circuit 5, and the input terminal of the current conditioning circuit 9 is connected with the output terminal of the output current sampling circuit 10. connected to the output.

The input DC voltage passes through the input filter circuit 1, the auxiliary power supply provides the working voltage of the drive control circuit 7, the drive control circuit 7 generates the drive signal of the power switch tube in the power conversion circuit 2, and is isolated and coupled by the high frequency transformer 3, and the output is passed through The output rectification circuit 4 and the output filter circuit 5 obtain the required DC voltage. In order to realize the stability of the output voltage, the output feedback control circuit 8 adopts the direct sampling of the output voltage, and controls the duty ratio of the pulse width modulator in the drive control circuit 7 after comparison with the reference voltage, amplification and isolation feedback, thereby realizing the output voltage closed-loop control. The output current of the power supply passes through the output current sampling circuit 10 and outputs a voltage signal to the output feedback control circuit 8 through the current conditioning circuit 9 , and finally controls the voltage at both ends of the power supply load 6 .

As shown in Figure 2, the output current sampling circuit is composed of a sampling coil L2 and a resistor R; the sampling coil L2 and the output filter inductor L1 are wound on the same magnetic core, and the end of the sampling coil L2 with the same name as the output filter inductor L1 The opposite end of the sampling coil L2 is connected to the opposite end of the output filter inductor L1 through a resistor R. Inside the dotted line box is the output current sampling circuit 10 , and L1 is the output filter inductance in the output filter circuit 5 . The voltage at point A is the reference ground of the output voltage, and the voltage at point B is the product of the equivalent resistance of the output filter inductor L1 and the current flowing through the output filter inductor. The voltage signal at point B is the output signal of the output current sampling circuit 10 , and the current conditioning circuit 9 receives the output current sampling signal of the output current sampling circuit 10 .

As shown in Figure 3, the current conditioning circuit includes an amplifying circuit 11 composed of an amplifier U1 and a comparison circuit 12 composed of a comparator U2; the non-inverting input terminal of the amplifier U1 is connected to the opposite end of the sampling coil L2, and the output of the comparator U2 The terminal is connected with the output feedback control circuit. The output voltage signal of the output current sampling circuit 10 needs to be amplified by the amplifying circuit 11 in the current conditioning circuit 9, and the output signal of the amplifying circuit 11 is sent to the positive terminal of the comparator of the comparison circuit 12 and is inverted with the comparator of the comparison circuit 12. Compare to the reference signal at the end. When the output signal voltage of the amplifying circuit 11 is greater than the reference signal voltage of the comparator reverse end of the comparison circuit 12, the comparison circuit 12 outputs a high level, that is, the current conditioning circuit 9 outputs a high level; otherwise, the current conditioning circuit 9 outputs a low level flat. Here, the conductor material of the output filter inductor L1 is soft copper, and the temperature coefficient of copper is relatively large. Therefore, when the power supply load 6 is constant, the output signal voltage signal of the amplifier circuit 11 changes with the temperature, and the overall temperature is positive. characteristic. Therefore, the signal voltage at the inverting end of the comparator of the comparison circuit 12 also changes with temperature, and the change characteristic is consistent with the change characteristic of the output signal voltage signal of the amplifier circuit 11 with temperature.

The current conditioning circuit 9 receives the output signal of the output current sampling circuit 10 , sends the signal to the output feedback control circuit 8 after conditioning, and then controls the drive signal output of the drive control circuit 7 . When the power load 6 is not overloaded, the current conditioning circuit 9 outputs a low level. The output signal of the current conditioning circuit 9 has no effect on the output feedback control circuit 8, the drive control circuit 7 works normally, and the output voltage at both ends of the power supply load 6 is stable. When the power supply load 6 has a large overload, that is, the overcurrent point set by the switching power supply is reached, the current conditioning circuit 9 outputs a high level, and the output of the drive signal of the drive control circuit 7 is stopped through the output feedback control circuit 8, finally making the power supply load 6 The voltage across the terminal drops.

The working principle of the over-current protection circuit: Since the magnitude of the current sampling signal is generally only a few tens of millivolts, the signal is first amplified through the operational amplifier U1. The current sampling signal amplified by the operational amplifier U1 is input to the positive terminal of the comparator U2, and compared with the voltage value of the negative terminal of the comparator U2. When the power supply is working normally, the comparator does not flip; The current protection point (assumed to be 120% of the maximum load current), the comparator flips, and at this time, the output of U2 is high. U3 is a feedback comparator. When U2 outputs a high level, the reference voltage of U3 will be pulled down, so that the output voltage sampling signal is greater than the reference reference voltage, and the feedback comparator U3 outputs a low level, so that the conduction current of the transistor Q1 increases; when the conduction of the transistor Q1 When the current reaches 1mA, the primary pulse width controller of the power supply will stop outputting the two driving signals of the half bridge, and then pull down the output voltage. The circuit in the two boxes of signal amplification and signal comparison in Figure 3 is the actual circuit inside the current conditioning circuit 9, and the circuit after the output of U2 in the figure is the output feedback control circuit (this control circuit is a type III feedback compensation commonly used in switching power supplies circuit).

The present invention mainly uses the specific law between the equivalent resistance of the output filter inductor L1 in the output filter circuit 5 and the output current to perform signal sampling, and its advantage is that the sampling circuit can almost achieve no power loss, which improves the power supply efficiency. Certain conditions are created, the output efficiency of the switching power supply is improved, the line loss of the circuit is reduced, and the anti-interference ability is strong. The sampling coil L2 is wound on the output filter inductor L1, both of which are wound on the same magnetic core, the sampling circuit components are less, and the implementation is convenient. In addition, the current conditioning circuit 9 only needs to solve the temperature characteristics and matching problems of the reference signal voltage at the comparator inverting end of the comparator circuit 12 to obtain a good overcurrent protection effect. Working within the temperature range of -55°C to +125°C, it can achieve effective overcurrent protection when the power supply load exceeds 1.4 times the rated load, and the product has high integration and good reliability.

Claims (3)

1. A switching power supply protection circuit, comprising an input filter circuit, a power conversion circuit, a high-frequency transformer, an output rectifier circuit, an output filter circuit, a drive control circuit, an output feedback control circuit, an overcurrent protection circuit, and the output filter circuit includes The output filter inductor L1 is characterized in that: the overcurrent protection circuit includes a current conditioning circuit and an output current sampling circuit; the input filter circuit is respectively connected to the output terminal of the drive control circuit and the high The input terminal of the high-frequency transformer is connected; the input terminal of the drive control circuit is connected with the output terminal of the input filter circuit and the output terminal of the output feedback control circuit; the output terminal of the high-frequency transformer is connected through the output rectifier circuit , the output filter circuit is connected to the power supply load; the output end of the output filter circuit is connected to the input end of the output current sampling circuit, the input end of the output feedback control circuit is connected to the output end of the current conditioning circuit, and the output end of the output filter circuit connected, the input end of the current conditioning circuit is connected to the output end of the output current sampling circuit; The current conditioning circuit includes an amplifying circuit (11) composed of an operational amplifier U1 and a comparison circuit (12) composed of a comparator U2. The inverting input terminal of the operational amplifier U1 is connected to the output of the output current sampling circuit via a resistor R1 The non-inverting input terminal of the operational amplifier U1 is connected to the ground, the output terminal of the operational amplifier U1 is connected to the non-inverting input terminal of the comparator U2, the inverting input terminal of the comparator U2 is connected to the power supply through the resistor R3, and the output terminal of the comparator U2 is connected to the The input end of the output feedback control circuit is connected; The output feedback control circuit includes a resistor R5, a transistor Q1 and a feedback comparator U3, the base of the transistor Q1 is connected to the output terminal of the comparator U2 through a resistor R5, the emitter of the transistor Q1 is grounded, and the collector of the transistor Q1 is connected to the The non-inverting input terminal of the feedback comparator U3 is connected, the inverting input terminal of the feedback comparator U3 is an output voltage sampling signal terminal, and the non-inverting input terminal thereof is a reference voltage terminal. 2. A switching power supply protection circuit according to claim 1, characterized in that: the output current sampling circuit is composed of a sampling coil L2 and a resistor R; the sampling coil L2 and the output filter inductor L1 are wound on the same On the magnetic core, the same-name end of the sampling coil L2 is connected to the same-name end of the output filter inductor L1, and the opposite-name end of the sampling coil L2 is connected to the same-name end of the output filter inductor L1 through a resistor R, and the same-name end of the sampling coil L2 is the output current The input end of the sampling circuit, the opposite end of the sampling coil L2 is the output end of the output current sampling circuit. 3. A kind of switching power supply protection circuit control method according to claim 1, is characterized in that, comprises the following steps, a: The current sampling signal is amplified through the operational amplifier U1; b: The current sampling signal amplified by the operational amplifier U1 is input to the non-inverting terminal of the comparator U2, and compared with the voltage value of the inverting terminal of the comparator U2. When the switching power supply is working normally, the comparator U2 does not flip; when When the load current reaches the overcurrent protection point, the comparator U2 flips, and at this time, the output of the comparator U2 is high; c: Send the output signal of the comparator U2 to the feedback comparator U3 in the output feedback control circuit. When the comparator U2 outputs a high level, the reference reference voltage of the feedback comparator U3 is pulled down, and the output voltage sampling signal is greater than the reference reference voltage , the feedback comparator U3 outputs a low level, and the conduction current of the transistor Q1 increases; when the conduction current of the transistor Q1 reaches 1mA, the primary pulse width controller of the switching power supply stops outputting the two-way driving signals of the half bridge, and the output voltage is pulled Low.