CN108832667B - A soft-start control circuit applied to control DC output of switching power supply - Google Patents

Abstract

The invention relates to a soft start control circuit applied to control the direct current output of a switching power supply, comprising a control switch tube module and a linear optocoupler module; the input end of the control switch tube module is used for connecting the direct current output starting signal of the switching power supply, and the output end is connected to the linear The primary loop of the optocoupler module and the secondary loop of the linear optocoupler module are used to connect the control circuit of the DC output of the switching power supply. When receiving the DC output start signal of the switching power supply, the invention controls the switching tube module to be in a linear amplification state, the secondary side loop voltage of the linear optocoupler module changes slowly, and the secondary side of the linear optocoupler module is directly connected to the output control end of the switching power supply. The given value of the output voltage of the DC switching power supply is gradually climbed to the final given value, which effectively avoids the phenomenon of output overshoot caused by the slow closed-loop regulation loop speed and the high voltage of the initial output given control pin when the DC switching power supply is started.

Description

A soft-start control circuit applied to control DC output of switching power supply

technical field

The invention relates to a soft start control circuit applied to control the direct current output of a switching power supply, and belongs to the technical field of electronic circuits.

Background technique

For some existing DC switching power supply devices, when the load is started, when the output closed-loop regulation circuit is powered before the output of the switching power supply and the closed-loop regulation speed is slow, it is easy to cause a large voltage and current overshoot, and the DC switch The power supply causes some damage. Therefore, how to effectively avoid the overvoltage or overcurrent of the DC switching power supply device when it is started with load is extremely important for protecting the DC switching power supply device.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a soft-start control circuit applied to control the DC output of a switching power supply, which is used to solve the problem of output overshoot when the DC switching power supply device is started with a load.

In order to solve the above technical problems, the present invention provides a soft-start control circuit applied to control the DC output of a switching power supply, including a control switch tube module and a linear optocoupler module; the input end of the control switch tube module is used to connect the switching power supply The DC output start signal, the output end of which is connected to the primary side loop of the linear optocoupler module, is used to: control the switching tube module to charge when the DC output start signal of the switching power supply is not received, and start when the DC output of the switching power supply is received. When the signal is received, the switch tube module is controlled to discharge to provide a gradually decreasing current to the primary loop of the linear optocoupler module; the secondary loop of the linear optocoupler module is used to connect the control circuit of the DC output of the switching power supply.

The beneficial effects of the invention are: when there is a direct current output starting signal of the switching power supply, the control switch tube module is in a linear amplification state, and the secondary side loop voltage of the linear optocoupler module changes slowly at this time, and the secondary side of the linear optocoupler module is directly connected. To the output control terminal of the switching power supply, the given value of the output voltage of the DC switching power supply gradually climbs to the final given value, so as to achieve the effect of the slow change of the output control terminal of the switching power supply, which effectively avoids the closed-loop adjustment loop speed when the DC switching power supply starts. Slow and initial output given control pin voltage is too high to cause output overshoot phenomenon.

Further, in order to realize the control of the output soft-start time of the DC switching power supply, the control switch tube module is connected to the switching power supply DC output start signal through a timing module, which is used to set the DC output start signal after receiving the switching power supply DC output start signal. The time delay charges the control switch tube module.

Further, in order to control the control switch tube module to be in a linear amplification state after a set time delay after receiving the start signal, the control switch tube module includes a first transistor, and the base of the first transistor is connected to In the timing module, a ground capacitor is also connected between the timing module and the base of the first triode, and the collector of the first triode is connected to the primary loop of the linear optocoupler module, so the The emitter of the first triode is grounded.

Further, in order to control the current of the control switch tube module during the charging and discharging process, the timing module and the base of the first triode and the base of the first triode and the ground are both connected. There is a resistor in series.

Further, in order to realize the timing function, the timing module includes a second triode and a double D flip-flop; the base of the second triode is used to connect the switching power supply DC to output a start signal, and the second triode is used to output a start signal. The collector of the tube is connected to the first terminal of a first resistance-capacitance charge and discharge module, the second terminal of the first resistance-capacitance charge and discharge module is connected to the reset terminal of the double D flip-flop, the second three The emitter of the pole tube is grounded; the base of the second transistor is also connected to the first terminal of a second resistance-capacitance charge and discharge module, and the second terminal of the second resistance-capacitance charge and discharge module is connected to the The set terminal of the double D flip-flop.

Further, in order to realize the control of the timing module, the RC charging and discharging module includes a first resistor, a second resistor and a charging and discharging capacitor, and the first resistor is arranged in series on the first wiring of the RC charging and discharging module. Between the terminal and the second terminal, the second resistor and the charging and discharging capacitor are connected in parallel, one parallel point of the second resistor and the charging and discharging capacitor is grounded, and the other parallel point is connected to the first parallel point of the resistance-capacitor charging and discharging module. Two terminals.

Description of drawings

1 is a schematic structural diagram of a soft-start control circuit applied to control the DC output of a switching power supply;

FIG. 2 is a circuit diagram of a soft-start control circuit applied to control the DC output of the switching power supply.

Detailed ways

In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

The present invention provides a soft-start control circuit applied to control the DC output of a switching power supply, the schematic diagram of which is shown in Figure 1, including a switching power supply DC output initial given voltage control pin start-up time timing circuit, and an optocoupler to form an output linear circuit And the DC output closed-loop regulation circuit of the switching power supply. Among them, the input terminal of the switching power supply DC output initial given voltage control pin start-up time timing circuit is used to receive the switching power supply DC output start signal, and its output terminal is connected to the input terminal of the output linear circuit formed by the optocoupler, and the optocoupler formed the output linear circuit. The output terminal is connected to the DC output control terminal of the switching power supply and the DC output closed-loop regulating circuit of the switching power supply.

Among them, the switching power supply DC output start signal is the switching power supply output enable signal. When the switching power supply receives this signal, the output side of the switching power supply starts to output.

As shown in Figure 2, the switching power supply DC output initial given voltage control pin start-up time timing circuit (timing module) includes a second transistor Q1 and a double D flip-flop U1A, the base of the second transistor Q1 passes through the resistor R1 Connect the switching power supply to the DC output start signal, the collector of the second transistor Q1 is connected to the first terminal of a first resistance-capacitance charge and discharge module, and the second terminal of the first resistance-capacitance charge and discharge module is connected to the double D flip-flop. Reset terminal R. The base of the second transistor Q1 is connected to the first terminal of a second RC charge-discharge module through the resistor R1, and the second terminal of the second RC charge-discharge module is connected to the set terminal S of the double D flip-flop . The output end Q of the double D flip-flop is used as the output end of the whole timing module, which is used to connect the input end of the optocoupler to form the output linear circuit.

Wherein, for each RC charging and discharging module, the RC charging and discharging module includes a first resistor, a second resistor, a charging and discharging capacitor, a first terminal and a second terminal, and the first resistor is serially connected to the RC charging and discharging module. Between the first terminal and the second terminal, the second resistor and the charging and discharging capacitor are connected in parallel, one parallel point of the second resistor and the charging and discharging capacitor is grounded, and the other parallel point is connected to the second wiring of the resistance-capacitor charging and discharging module end.

In this embodiment, the model of the double D flip-flop is CD4013. Of course, as other implementation manners, other types of double D flip-flops may also be used under the condition that the timing requirements are met.

The output linear circuit composed of optocouplers is composed of a control switch tube module and a linear optocoupler module. The input end of the control switch tube module is connected to the output end of the timing module, and its output end is connected to the primary loop of the linear optocoupler module. The linear optocoupler module The secondary side loop is used to connect the control circuit of the DC output of the switching power supply.

As shown in Figure 2, the control switch tube module includes a first transistor Q2, the base of the first transistor Q2 is connected to the timing module, and a ground is also connected between the timing module and the base of the first transistor Q2 Capacitor C3, the collector of the first transistor Q2 is connected to the primary loop of the linear optocoupler module, and the emitter of the first transistor Q2 is grounded. In addition, in order to better realize the charge and discharge control of the ground capacitor C3, a resistor R9 is connected in series between the base of the first transistor Q2 and the timing module, and between the base of the first transistor Q2 and the ground Resistor R10 is arranged in series.

The linear optocoupler module is composed of a linear optocoupler O1. The primary loop of the linear optocoupler O1 is connected to the output end of the control switch tube module. One terminal in the secondary loop of the linear optocoupler O1 is grounded, and the other terminal is used for It is connected to the DC output control terminal of the switching power supply, and is connected to the DC closed-loop regulating output terminal of the switching power supply through a resistor R12, and the DC closed-loop regulating output terminal of the switching power supply is connected to the DC output closed-loop regulating circuit of the switching power supply.

When the switching power supply receives the DC output start signal, the DC closed-loop regulation output terminal of the switching power supply is pulled down by the secondary side of the linear optocoupler connected to the output control terminal of the switching power supply, and the switching power supply DC outputs a low voltage. The secondary side voltage rises slowly until the switching power supply outputs the closed-loop regulation voltage, completing the switching process from the soft-start circuit to the closed-loop regulation circuit.

The working principle of the above-mentioned soft-start control circuit applied to control the DC output of the switching power supply is as follows: when the timing module does not receive the start signal on the DC output side of the switching power supply, that is, when the DC output of the switching power supply does not start, the DC output start signal of the switching power supply is high. flat. At this time, the reset terminal R of the double D flip-flop U1A is connected to a low level, the set terminal S of the double D flip-flop is connected to a high level, and the output terminal Q of the timing module formed by the transistor Q1 and the double D flip-flop U1A is High level, the voltage of the DC output control terminal of the switching power supply is pulled down by the output linear circuit composed of the optocoupler.

When the timing module receives the start signal of the DC output side of the switching power supply, that is, when the DC output of the switching power supply is started, the DC output start signal of the switching power supply is at a low level. At this time, the power supply VCC charges the capacitor C1 through the resistors R3 and R4, the capacitor C2 discharges through the resistor R7, the low level connected to the reset terminal R of the double D flip-flop U1A turns to a high level, and the double D flip-flop is set. The high level connected to the terminal S is turned to a low level, and the output Q of the double D flip-flop is turned from a high level to a low level. By adjusting the parameter values of R3, R4, R5 and C1, as well as the parameter values of resistor R7 and capacitor C2, the time when pin 1 of U1A is turned from high level to low level can be determined. By setting the timing module, after setting the start-up time, the required level signal can be output to the optocoupler to form an output linear circuit, thereby turning on the output linear circuit.

When the output terminal Q of the timing module changes to a low level, in the process of continuous discharge of the capacitor C3, the collector current of the transistor Q2 in the amplifying state gradually becomes smaller, so that the current size of the primary side of the optocoupler is adjusted, and the optocoupler The secondary voltage changes slowly. Since R8, R9, R10, R11, R12, Q2 and O1 form an output linear circuit, by adjusting the parameter values of C3, R9, R11 and R12, the secondary side of the optocoupler O1 can output an ideal level value, thus realizing the ideal level when R8 When switching with U1A, the purpose of smooth transition of the secondary side of O1. Since the secondary side of optocoupler O1 is directly connected to the output control terminal of the switching power supply, and is connected to the DC closed-loop regulating output terminal of the switching power supply through the resistor R12, when the clamping level of the secondary side of O1 is higher than the output signal of the output closed-loop regulating circuit of the switching power supply, the switching power supply The signal of the DC output control terminal is switched to the output level signal of the switching power supply output closed-loop adjustment circuit, so that the control voltage of the DC output control terminal of the switching power supply slowly climbs exponentially until the closed-loop adjustment of the given voltage. The DC output closed-loop adjustment circuit of the switching power supply outputs the voltage required by the control terminal of the switching power supply by passing the output detection signal and the output given signal through the PID (proportional integral derivative circuit) circuit, so that the output reaches the given value, and finally completes the DC output soft start of the switching power supply . Since the specific structure of the DC output closed-loop regulating circuit of the switching power supply belongs to the prior art, it will not be repeated here.

The soft-start control circuit applied to control the DC output of the switching power supply of the present invention outputs the start signal through the DC switching power supply, and outputs the soft-start time, the initial setting value of the output control pin of the switching power supply and the initial setting of the output control pin to the DC switching power supply. Set the value climbing rate, and make the output voltage given value gradually climb to the final given value of the DC switching power supply to avoid the slow closed-loop adjustment loop speed and the high voltage of the initial output given control pin when the DC switching power supply starts. The output overshoot effectively solves the problem of output overshoot when the power supply is initially powered on, and avoids the damage caused to the DC switching power supply.

In addition, it should be noted that the soft-start control circuit of the present invention can also not set the timing module, and directly connect the start signal of the DC output side of the switching power supply to the optocoupler composed of the control switch tube module and the linear optocoupler module to form an output linear circuit , When receiving the start signal of the DC output side of the switching power supply, the optocoupler is directly started to form an output linear circuit to realize the soft start of the DC output of the switching power supply.

The above description is only used to help understand the method and core idea of the present invention. For those of ordinary skill in the art, according to the guiding idea of the present invention, various deformation models and parameter modifications designed still fall within the protection scope of the present invention.

Claims (4)

1. A soft-start control circuit applied to control the DC output of a switching power supply, characterized in that it includes a control switch tube module and a linear optocoupler module; the input end of the control switch tube module is used to connect the DC output start signal of the switching power supply , the output end of which is connected to the primary side loop of the linear optocoupler module, which is used to: control the switching tube module to charge when the DC output start signal of the switching power supply is not received, and control the switching power supply when receiving the DC output start signal of the switching power supply. The switching tube module discharges to provide a gradually decreasing current to the primary loop of the linear optocoupler module; a terminal of the secondary loop of the linear optocoupler module is used for the same time as the output end of the DC output closed-loop regulation circuit of the switching power supply Connect the DC output control terminal of the switching power supply; When the secondary clamping level of the linear optocoupler module is higher than the output level of the DC output closed-loop adjustment circuit of the switching power supply, the level signal of the DC output control terminal of the switching power supply is switched to the output level signal of the DC output closed-loop adjustment circuit of the switching power supply, so that the switch The control voltage of the DC output control terminal of the power supply climbs slowly and exponentially until the closed-loop adjustment of the given voltage; the DC output closed-loop adjustment circuit of the switching power supply outputs the voltage required by the control terminal of the switching power supply by passing the output detection signal and the output given signal through the PID circuit; The control switch tube module is connected to the switching power supply DC output start signal through a timing module, and is used for charging the control switch tube module after a set time delay after receiving the DC output start signal of the switching power supply; The timing module includes a second triode and a double D flip-flop; the base of the second triode is used to connect the switching power supply to output a direct current start signal, and the collector of the second triode is connected to a first The first terminal of the resistance-capacitance charge-discharge module, the second terminal of the first resistance-capacitance charge-discharge module is connected to the reset terminal of the double D flip-flop, and the emitter of the second triode is grounded; The base of the second triode is also connected to the first terminal of a second resistance-capacitance charge and discharge module, and the second terminal of the second resistance-capacitance charge and discharge module is connected to the set connection of the double D flip-flop end. 2 . The soft-start control circuit applied to control the DC output of a switching power supply according to claim 1 , wherein the control switch tube module comprises a first triode, and the base of the first triode is connected to the base. 3 . In the timing module, a ground capacitor is also connected between the timing module and the base of the first triode, and the collector of the first triode is connected to the primary loop of the linear optocoupler module, so the The emitter of the first triode is grounded. 3 . The soft-start control circuit applied to control the DC output of a switching power supply according to claim 2 , wherein the timing module and the base of the first triode and between the base of the first triode 3 . Resistors are connected in series between the base and the ground. 4 . The soft-start control circuit applied to control the DC output of a switching power supply according to claim 1 , wherein the RC charging and discharging module comprises a first resistor, a second resistor and a charging and discharging capacitor, and the first A resistor is arranged in series between the first terminal and the second terminal of the resistance-capacity charge-discharge module, the second resistor and the charge-discharge capacitor are connected in parallel, and a parallel point of the second resistor and the charge-discharge capacitor is grounded , and the other parallel point is connected to the second terminal of the RC charging and discharging module.

Images