A starting circuit for a switching power supply

Abstract

This utility model relates to the field of switching power supply technology, specifically to a startup circuit for a switching power supply, including a startup input port, a power supply input port, a PWM control chip U1, a startup module, a power supply module, and a linear regulator module. The startup module includes a capacitor C3, a resistor R12, a diode D2, and a switching transistor Q2. The power supply module includes a capacitor C2, a resistor R4, and a resistor R8. The linear regulator module includes a switching transistor Q3 and a resistor R5. By incorporating the startup module, power supply module, and linear regulator module, this utility model ensures that when the switching power supply is disconnected, no residual voltage is transmitted to the power supply terminal of the PWM control chip U1, allowing the power supply terminal of the PWM control chip U1 to initialize quickly. When a startup power supply is input again to the startup input port, the PWM control chip U1 can also start up quickly and normally.

Description

Technical Field

[0001] This utility model relates to the field of switching power supply technology, and specifically to a startup circuit for a switching power supply. Background Technology

[0002] The Vcc startup circuit is an important part of the switching power supply used to start the PWM control chip. It is responsible for providing initial energy when the power is turned on, so that the power supply can start normally and enter a stable working state. The commonly used startup circuit is the resistor startup circuit, which can be in the form of DC startup, AC startup, and linear voltage regulator circuit.

[0003] The advantages of DC starting circuits are simple circuit structure and low cost. The disadvantage is that when the AC power is disconnected, the switching power supply stops working, but the remaining energy of the BUCK capacitor will continue to charge the power supply capacitor through the starting resistor. When the voltage of the power supply capacitor reaches the starting threshold of the PWM control chip, it will restart a second time, which will affect the malfunction of the powered equipment.

[0004] The advantages of AC start-up circuits are simple circuit structure and low cost. The disadvantage is that when using a PWM control chip with abnormal protection lock-up function, during the power outage recovery and restart process, the voltage at the power supply terminal cannot be quickly reduced to its shutdown threshold, which prolongs the chip initialization and restart time and affects the use of the powered equipment.

[0005] The advantages of linear voltage regulator circuits are simple circuit structure and low cost. The disadvantage is that when the power is switched on, the potential difference before and after linear regulation is large, which increases the voltage difference between the emitter and base of the switching transistor, leading to the risk of the switching transistor breaking down. Utility Model Content

[0006] The purpose of this invention is to address the aforementioned shortcomings in the prior art by providing a startup circuit for a switching power supply.

[0007] The purpose of this utility model is achieved through the following technical solution: a startup circuit for a switching power supply, including a startup input port, a power supply input port, a PWM control chip U1, a startup module, a power supply module, and a linear voltage regulator module;

[0008] The startup module includes capacitor C3, resistor R12, diode D2, and switching transistor Q2; the power supply module includes capacitor C2, resistor R4, and resistor R8; the linear regulator module includes switching transistor Q3 and resistor R5.

[0009] One end of capacitor C3 is connected to the start input port; the other end of capacitor C3 is grounded; resistor R12 is connected in parallel with capacitor C3; one end of capacitor C3 is connected to the control terminal of switch Q2; one end of the switch terminal of switch Q2 is grounded; diode D2 is located at one end of capacitor C3 and connected to the other end of the switch terminal of switch Q2; the other end of the switch terminal of switch Q2 is connected to the control terminal of switch Q3.

[0010] The power input port is connected to one end of resistor R4; the other end of resistor R4 is grounded through capacitor C2; the other end of resistor R4 is connected to the control terminal of switch Q3 through resistor R8.

[0011] One end of the switching transistor Q3 is connected to the other end of the resistor R4; the other end of the switching transistor Q3 is connected to the power supply terminal of the PWM control chip U1 through the resistor R5.

[0012] The present invention is further configured such that the start input port includes a positive start input port; the start module also includes resistors R3, R9 and R10.

[0013] The positive start input port is connected to one end of resistor R3 after passing through resistor R9 and resistor R10 in sequence; the other end of resistor R3 is connected to one end of capacitor C3.

[0014] The present invention is further configured such that the start input port includes a negative start input port; the start module also includes resistors R1 and R2;

[0015] The negative start input port is connected to one end of resistor R3 after passing through resistor R1 and resistor R2 in sequence.

[0016] The present invention is further configured such that the switching transistor Q2 is a PNP transistor; and the switching transistor Q3 is an NPN transistor;

[0017] One end of capacitor C3 is connected to the positive terminal of diode D2; the negative terminal of diode D2 is connected to the emitter of switching transistor Q2; one end of capacitor C3 is connected to the base of switching transistor Q2; the collector of switching transistor Q2 is grounded; and the emitter of switching transistor Q2 is connected to the base of switching transistor Q3.

[0018] The other end of the resistor R4 is connected to the base of the switching transistor Q3 through the resistor R8.

[0019] The collector of the switching transistor Q3 is connected to the other end of the resistor R4; the emitter of the switching transistor Q3 is connected to the power supply terminal of the PWM control chip U1 through the resistor R5.

[0020] The present invention is further configured such that the start-up module also includes a resistor R13; the collector of the switch transistor Q2 is grounded through the resistor R13.

[0021] The present invention is further configured such that the linear voltage regulator module also includes a capacitor C4; the emitter of the switching transistor Q3 is grounded through the capacitor C4.

[0022] The present invention is further configured such that the linear voltage regulator module also includes a Zener diode ZD1; the positive terminal of the Zener diode ZD1 is grounded; and the negative terminal of the Zener diode ZD1 is connected to the base of the switching transistor Q3.

[0023] The present invention is further configured such that the power supply module also includes a diode D1; the power supply input port is connected to the positive terminal of the diode D1; and the negative terminal of the diode D1 is connected to one end of the resistor R4.

[0024] The beneficial effects of this utility model are as follows: By setting up a startup module, a power supply module, and a linear voltage regulator module, this utility model ensures that when the switching power supply is disconnected, no residual voltage is transmitted to the power supply terminal of the PWM control chip U1, so that the power supply terminal of the PWM control chip U1 can be quickly initialized. When the startup power is input again at the startup input port, the PWM control chip U1 can also start up quickly and normally. Attached Figure Description

[0025] The utility model will be further described with reference to the accompanying drawings, but the embodiments in the drawings do not constitute any limitation on the present utility model. For those skilled in the art, other drawings can be obtained based on the following drawings without creative effort.

[0026] Figure 1 This is the circuit schematic diagram of this utility model;

[0027] Among them: 1. Positive start input port; 2. Negative start input port; 3. Power supply input port. Detailed Implementation

[0028] The present invention will be further described in conjunction with the following embodiments.

[0029] Depend on Figure 1As can be seen, the startup circuit of the switching power supply described in this embodiment includes a startup input port, a power supply input port 3, a PWM control chip U1, a startup module, a power supply module, and a linear regulator module; the startup module includes a capacitor C3, a resistor R12, a diode D2, and a switching transistor Q2; the power supply module includes a capacitor C2, a resistor R4, and a resistor R8; the linear regulator module includes a switching transistor Q3 and a resistor R5; one end of the capacitor C3 is connected to the startup input port; the other end of the capacitor C3 is grounded; the resistor R12 is connected in parallel with the capacitor C3; one end of the capacitor C3 is connected to the control circuit of the switching transistor Q2. The circuit is connected as follows: one end of the switching terminal of the transistor Q2 is grounded; one end of the diode D2 is connected to one end of the capacitor C3 and the other end of the switching terminal of the transistor Q2; the other end of the switching terminal of the transistor Q2 is connected to the control terminal of the transistor Q3; the power input port 3 is connected to one end of the resistor R4; the other end of the resistor R4 is grounded through the capacitor C2; the other end of the resistor R4 is connected to the control terminal of the transistor Q3 through the resistor R8; one end of the switching terminal of the transistor Q3 is connected to the other end of the resistor R4; the other end of the switching terminal of the transistor Q3 is connected to the power supply terminal of the PWM control chip U1 through the resistor R5. This embodiment describes a startup circuit for a switching power supply. The switching transistor Q2 is a PNP transistor; the switching transistor Q3 is an NPN transistor; one end of capacitor C3 is connected to the anode of diode D2; the cathode of diode D2 is connected to the emitter of switching transistor Q2; one end of capacitor C3 is connected to the base of switching transistor Q2; the collector of switching transistor Q2 is grounded; the emitter of switching transistor Q2 is connected to the base of switching transistor Q3; the other end of resistor R4 is connected to the base of switching transistor Q3 via resistor R8; the collector of switching transistor Q3 is connected to the other end of resistor R4; and the emitter of switching transistor Q3 is connected to the power supply terminal of PWM control chip U1 via resistor R5.

[0030] Specifically, in the startup circuit of the switching power supply described in this embodiment, when the switching power supply is turned on, a startup power supply is first input into the startup input port. The startup power supply charges capacitor C3 to store energy. At the same time, diode D2 is forward-biased and conducts, causing the base potential of switching transistor Q3 to rise accordingly, and the emitter junction of switching transistor Q3 to be forward-biased and conduct. The DC voltage is then sent to the power supply terminal of PWM control chip U1 after being current-limited by resistor R5. The energy stored in capacitor C3 is continuously transferred to the power supply terminal of PWM control chip U1. When the voltage at the power supply terminal of PWM control chip U1 rises to the turn-on threshold of PWM control chip U1, PWM control chip U1 is started, thereby enabling power supply input into power input port 3. The power supply supplies power to the power supply terminal of PWM control chip U1 through resistor R4, capacitor C2, resistor R8, and resistor R5.

[0031] When the switching power supply is turned off, the startup power supply of the startup input port is disconnected, and capacitor C3 is no longer charged. At the same time, resistor R12 discharges the residual voltage of capacitor C3, the positive potential of diode D2 decreases and is reverse-biased and cut off, the base of switching transistor Q2 is at a low potential and is saturated and turned on, and the base potential of switching transistor Q3 is discharged, so that the power supply loop of switching transistor Q3 is turned off and the loop is opened. At this time, no energy is transferred to the power supply terminal of PWM control chip U1, and the voltage at the power supply terminal of PWM control chip U1 drops rapidly to the turn-off threshold of PWM control chip U1, and PWM control chip U1 turns off and stops working.

[0032] In this embodiment, when the switching power supply is disconnected, no residual voltage is transmitted to the power supply terminal of the PWM control chip U1, which enables the power supply terminal of the PWM control chip U1 to be initialized quickly. When the startup power is input again at the startup input port, the PWM control chip U1 can also start up quickly and normally.

[0033] The startup circuit of the switching power supply described in this embodiment includes a positive startup input port 1; the startup module also includes resistors R3, R9 and R10.

[0034] The positive start input port 1 is connected to one end of resistor R3 via resistors R9 and R10 in sequence; the other end of resistor R3 is connected to one end of capacitor C3. In this embodiment, the start circuit of a switching power supply further includes a negative start input port 2; the start module also includes resistors R1 and R2; the negative start input port 2 is connected to one end of resistor R3 via resistors R1 and R2 in sequence.

[0035] Specifically, in this embodiment, through the above-described configuration, AC power can be supplied between the positive start-up input port 1 and the negative start-up input port 2. The AC voltage is converged to resistor R3 through resistors R1, R2, R9, and R10 to form a pulsating voltage. Resistor R3 charges capacitor C3 to store energy. At the same time, diode D2 conducts forward to rectify the pulsating voltage into DC voltage. The starting energy is transferred to the power supply terminal of PWM control chip U1 through the forward bias conduction of the emitter junction of switching transistor Q3. This ensures that both the positive and negative half-cycles of the AC voltage participate in the startup process during the startup of the switching power supply, thus accelerating the startup time.

[0036] The startup circuit of the switching power supply described in this embodiment further includes a resistor R13; the collector of the switching transistor Q2 is grounded through resistor R13. Specifically, resistor R13 is a current-limiting resistor for the collector of the switching transistor Q2. When the switching power supply is turned off, the startup power supply at the startup input port is disconnected, and capacitor C3 is no longer charged. At the same time, resistor R12 discharges the residual voltage of capacitor C3, the positive potential of diode D2 decreases and is reverse-biased and cut off, and the base of switching transistor Q2 is at a low potential and saturates and conducts. The base potential of switching transistor Q3 is discharged through resistor R13, making the power supply loop of switching transistor Q3 open. At this time, no energy is transferred to the power supply terminal of PWM control chip U1, and the voltage at the power supply terminal of PWM control chip U1 drops rapidly to the turn-off threshold of PWM control chip U1, and PWM control chip U1 turns off and stops working.

[0037] The startup circuit of the switching power supply described in this embodiment includes a linear voltage regulator module, which further includes a capacitor C4; the emitter of the switching transistor Q3 is grounded through capacitor C4. The capacitor C4 serves a filtering function.

[0038] The startup circuit of the switching power supply described in this embodiment includes a linear voltage regulator module that further comprises a Zener diode ZD1; the positive terminal of the Zener diode ZD1 is grounded; and the negative terminal of the Zener diode ZD1 is connected to the base of the switching transistor Q3. Specifically, through the above configuration, the Zener diode ZD1 provides a reference potential to the base of the switching transistor Q3, thereby controlling the operating state of the switching transistor Q3 to achieve voltage regulation.

[0039] The startup circuit of the switching power supply described in this embodiment further includes a diode D1 in the power supply module; the power supply input port 3 is connected to the positive terminal of diode D1; and the negative terminal of diode D1 is connected to one end of resistor R4. This configuration rectifies the power supply input to the power supply input port 3.

[0040] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this utility model, and are not intended to limit the scope of protection of this utility model. Although this utility model has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of this utility model without departing from the essence and scope of the technical solutions of this utility model.

Claims

1. A startup circuit for a switching power supply, characterized in that: This includes a startup input port, a power supply input port (3), a PWM control chip U1, a startup module, a power supply module, and a linear voltage regulator module; The startup module includes capacitor C3, resistor R12, diode D2, and switching transistor Q2; the power supply module includes capacitor C2, resistor R4, and resistor R8; the linear regulator module includes switching transistor Q3 and resistor R5. One end of capacitor C3 is connected to the start input port; the other end of capacitor C3 is grounded; resistor R12 is connected in parallel with capacitor C3; one end of capacitor C3 is connected to the control terminal of switch Q2; one end of the switch terminal of switch Q2 is grounded; diode D2 is located at one end of capacitor C3 and connected to the other end of the switch terminal of switch Q2; the other end of the switch terminal of switch Q2 is connected to the control terminal of switch Q3. The power input port (3) is connected to one end of the resistor R4; the other end of the resistor R4 is grounded through the capacitor C2; the other end of the resistor R4 is connected to the control terminal of the switching transistor Q3 through the resistor R8. One end of the switching transistor Q3 is connected to the other end of the resistor R4; the other end of the switching transistor Q3 is connected to the power supply terminal of the PWM control chip U1 through the resistor R5.

2. The startup circuit of a switching power supply according to claim 1, characterized in that: The startup input port includes a positive startup input port (1); the startup module also includes resistors R3, R9 and R10; The positive start input port (1) is connected to one end of resistor R3 after passing through resistor R9 and resistor R10 in sequence; the other end of resistor R3 is connected to one end of capacitor C3.

3. The startup circuit of a switching power supply according to claim 2, characterized in that: The start input port also includes a negative start input port (2); the start module also includes resistors R1 and R2; The negative start input port (2) is connected to one end of resistor R3 after passing through resistor R1 and resistor R2 in sequence.

4. The startup circuit of a switching power supply according to claim 1, characterized in that: The switching transistor Q2 is a PNP transistor; the switching transistor Q3 is an NPN transistor; One end of capacitor C3 is connected to the positive terminal of diode D2; the negative terminal of diode D2 is connected to the emitter of switching transistor Q2; one end of capacitor C3 is connected to the base of switching transistor Q2; the collector of switching transistor Q2 is grounded; and the emitter of switching transistor Q2 is connected to the base of switching transistor Q3. The other end of the resistor R4 is connected to the base of the switching transistor Q3 through the resistor R8. The collector of the switching transistor Q3 is connected to the other end of the resistor R4; the emitter of the switching transistor Q3 is connected to the power supply terminal of the PWM control chip U1 through the resistor R5.

5. The startup circuit of a switching power supply according to claim 4, characterized in that: The startup module also includes a resistor R13; the collector of the switching transistor Q2 is grounded through the resistor R13.

6. The startup circuit of a switching power supply according to claim 4, characterized in that: The linear voltage regulator module also includes capacitor C4; the emitter of the switching transistor Q3 is grounded through capacitor C4.

7. The startup circuit of a switching power supply according to claim 4, characterized in that: The linear voltage regulator module also includes a Zener diode ZD1; the positive terminal of the Zener diode ZD1 is grounded; the negative terminal of the Zener diode ZD1 is connected to the base of the switching transistor Q3.

8. The startup circuit of a switching power supply according to claim 4, characterized in that: The power supply module also includes a diode D1; the power supply input port (3) is connected to the positive terminal of the diode D1; the negative terminal of the diode D1 is connected to one end of the resistor R4.

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