Short-circuit protection circuit and switching power supply circuit control device with same

Abstract

The utility model discloses a short-circuit protection circuit and a switching power supply control device, the short-circuit protection circuit comprises a VCC power supply circuit and a short-circuit detection circuit, the VCC power supply circuit is connected with a power supply voltage end of a control chip U2, the short-circuit detection circuit comprises a PNP type triode Q2, an NPN type triode Q3, a voltage stabilization source U3, a diode D2, a resistor R6 and a resistor R8, and the voltage stabilization source U3 is connected with the control chip U2. A COMP pin of the control chip U2 is grounded through a resistor R6 and a resistor R8 which are connected in series, a node between the resistor R6 and the resistor R8 which are connected in series is connected with a reference end of the voltage stabilizing source U3, a direct current voltage is connected with an emitting electrode of a PNP type triode Q2 and is connected to a cathode of the voltage stabilizing source U3 through a resistor, a base electrode of the PNP type triode Q2 is connected with an anode of a diode D2, a cathode of the diode D2 is connected with a cathode of the voltage stabilizing source U3, and a base electrode of the diode D2 is connected with an anode of the voltage stabilizing source U3. The anode of the voltage stabilizing source U3 is grounded, the collector electrode of the PNP type triode Q2 is grounded and connected with the anode of the diode D3, the cathode of the diode D3 is connected with the base electrode of the NPN type triode Q3, the emitter electrode of the NPN type triode Q3 is grounded, and the collector electrode of the NPN type triode Q3 serves as the output of the short circuit detection circuit to be connected to the VCC power supply circuit and used for controlling the on-off of the VCC power supply circuit. Under the condition that the output of the power supply circuit is short-circuited, the output short-circuit current can be reduced by adopting the technical scheme of the utility model.

Description

Technical Field

[0001] This utility model relates to the field of power supply circuit technology, and in particular to a short-circuit protection circuit and a power supply circuit control device having the circuit. Background Technology

[0002] A PWM control chip is a key component used to control power supply circuits. It controls the output voltage and current by adjusting the width (duty cycle) of the pulse signal. The UC2845 series of current-mode PWM control chips, as a classic control chip, uses a fixed-frequency PWM control method. It controls the power supply output voltage by continuously adjusting the duty cycle of the switching transistor. Due to its simple structure, ease of use, and minimal external circuitry, it is widely used in various low-power power supply circuits.

[0003] Hiccup mode in a power supply circuit is a protection mechanism primarily used to handle output short circuits. When the power supply circuit detects an output short circuit, hiccup mode is activated. The power chip operates for several hundred milliseconds, then stops operating for a few seconds, continuously cycling until the short circuit fault is cleared. This periodic operation and shutdown helps the system maintain a certain level of stability under short-circuit conditions.

[0004] When a PWM control chip is used in a switching power supply circuit with a short circuit at the output, the hiccup cycle of the control chip becomes uncontrollable, and the output short circuit current is large, which leads to excessive temperature rise of the output rectifier tube. Prolonged short circuit can damage the output rectifier tube, causing the power supply circuit to malfunction and affecting the reliability of the entire circuit system. Utility Model Content

[0005] The technical problem to be solved by this invention is how to control the hiccup cycle of the control chip under the condition of a short circuit in the power supply circuit output, thereby reducing the output short circuit current.

[0006] This utility model solves the above-mentioned technical problems through the following technical means: a short-circuit protection circuit, including a VCC power supply circuit and a short-circuit detection circuit. The VCC power supply circuit is connected to the power supply voltage terminal of the PWM control chip U2. The short-circuit detection circuit includes a PNP transistor Q2, an NPN transistor Q3, a voltage regulator U3, a diode D2, a resistor R6, and a resistor R8. The COMP pin of the PWM control chip U2 is grounded through the series resistors R6 and R8. The junction between the series resistors R6 and R8 is connected to the reference terminal of the voltage regulator U3. A DC voltage is connected to... The emitter of PNP transistor Q2 is connected to the cathode of Zener source U3 via a resistor. The base of PNP transistor Q2 is connected to the anode of diode D2. The cathode of diode D2 is connected to the cathode of Zener source U3. The anode of Zener source U3 is grounded. The collector of PNP transistor Q2 is grounded and connected to the anode of diode D3. The cathode of diode D3 is connected to the base of NPN transistor Q3. The emitter of NPN transistor Q3 is grounded. The collector is connected to the VCC power supply circuit as the output of the short-circuit detection circuit to control the on / off state of the VCC power supply circuit.

[0007] As a further optimized technical solution, the VCC power supply circuit includes an NPN transistor Q1, a Zener diode D1, a resistor R3, a capacitor C3, and a capacitor C4. The collector of the NPN transistor Q1 is connected to a DC voltage, which is simultaneously grounded through the series resistor R3 and capacitor C4. The base of the NPN transistor Q1 is connected to the cathode of the Zener diode D1, and the anode of the Zener diode D1 is grounded. The emitter of the NPN transistor Q1 is connected to the VCC pin of the control chip U2, and the emitter is grounded through capacitor C3. The collector of the NPN transistor Q3 is connected to the junction between the base of the NPN transistor Q1 in the VCC power supply circuit and the series resistor R3 and capacitor C4.

[0008] As a further optimized technical solution, the short-circuit detection circuit also includes capacitor C5, which is connected in parallel across resistor R8.

[0009] As a further optimized technical solution, the short-circuit detection circuit also includes resistor R9 and capacitor C6. The collector of PNP transistor Q2 is grounded through resistor R9, and capacitor C6 is connected in parallel across resistor R9.

[0010] As a further optimized technical solution, the short-circuit detection circuit also includes a resistor R7 and a capacitor C7. The cathode of the diode D3 is connected to one end of the resistor R7 and the capacitor C7, the other end of the resistor R7 is connected to the base of the NPN transistor Q3, and the other end of the capacitor C7 is grounded.

[0011] As a further optimized technical solution, the short-circuit detection circuit also includes resistors R4 and R5. The DC voltage is connected to the cathode of the voltage regulator U3 through the series resistors R4 and R5, and the cathode of the diode D2 is connected to the junction between the series resistors R4 and R5.

[0012] As a further optimized technical solution, the short-circuit protection circuit also includes an output voltage feedback circuit connected to the COMP pin of the PWM control chip U2.

[0013] As a further optimized technical solution, the output voltage feedback circuit includes an opto-isolator U1, resistors R1 and R2, and a capacitor C2. The anode of the input terminal of the opto-isolator U1 is connected to the output voltage +Vo through resistor R1, and the cathode of the input terminal is connected to the output voltage feedback signal Vo_FB. Resistor R2 is connected between the anode and cathode of the input terminal of the opto-isolator U1. The collector of the output terminal of the opto-isolator U1 is connected to the COMP pin of the control chip U2, the emitter of the output terminal is grounded, and a capacitor C2 is connected in parallel between the collector and emitter of the output terminal.

[0014] As a further optimized technical solution, the voltage regulator U3 is a controllable precision voltage regulator TL431.

[0015] The present invention also provides a switching power supply control device employing the short-circuit protection circuit described in any of the above-mentioned schemes, including a PWM control chip U2 and a short-circuit protection circuit connected to the PWM control chip U2.

[0016] The advantages of this invention are as follows: When a PWM control chip is applied to a power supply circuit via a short-circuit detection circuit, the hiccup cycle of the control chip is controllable under short-circuit conditions at the power supply output, reducing the output short-circuit current and controlling the temperature rise of the output rectifier diode. Prolonged short circuits will not damage the output rectifier diode. This short-circuit protection circuit overcomes the shortcomings of PWM control chips in the event of a short circuit at the power supply output. The circuit structure is simple, the cost is low, and it has practical application value in real-world circuits. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the short-circuit protection circuit according to an embodiment of the present invention. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of the embodiments of this utility model clearer, the technical solutions of the embodiments of this utility model will be clearly and completely described below in conjunction with the embodiments of this utility model. Obviously, the described embodiments are only some embodiments of this utility model, not all embodiments. Based on the embodiments of this utility model, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of this utility model.

[0019] Example 1

[0020] like Figure 1 As shown, taking the UC2845 current-mode PWM control chip U2 as an example, the structure and working principle of the short-circuit protection circuit of this utility model are explained. This utility model provides a short-circuit protection circuit, including a VCC power supply circuit, an output voltage feedback circuit, and a short-circuit detection circuit.

[0021] The VCC power supply circuit includes an NPN transistor Q1, a Zener diode D1, a resistor R3, and capacitors C3 and C4. The collector of NPN transistor Q1 is connected to a +24V DC voltage, which is simultaneously grounded through the series resistor R3 and capacitor C4. The base of NPN transistor Q1 is connected to the cathode of Zener diode D1, and the anode of Zener diode D1 is grounded. The emitter of NPN transistor Q1 serves as the output terminal of the +Vcc supply voltage, connected to the VCC pin of control chip U2, and grounded through capacitor C3. This VCC power supply circuit, through a linear voltage regulator circuit composed of NPN transistor Q1 and Zener diode D1, converts the +24V DC voltage to the +Vcc supply voltage required by control chip U2.

[0022] The output voltage feedback circuit includes an opto-isolator U1, resistors R1 and R2, and capacitor C2. Opto-isolator U1 can be any common existing opto-isolator, such as TLP521 or PC817. The anode of the input terminal of opto-isolator U1 is connected to the output voltage +Vo through resistor R1, and the cathode of the input terminal is connected to the output voltage feedback signal Vo_FB. Resistor R2 is connected between the anode and cathode of the input terminal of opto-isolator U1. The collector of the output terminal of opto-isolator U1 is connected to the COMP pin of control chip U2, and the emitter of the output terminal is grounded. A capacitor C2 is connected in parallel between the collector and emitter of the output terminal. This output voltage feedback circuit sends the feedback signal Vo_FB, which is required to achieve the output voltage +Vo, to the COMP pin of control chip U2 through opto-isolator U1, serving as the control signal for closed-loop control of control chip U2.

[0023] The short-circuit detection circuit includes a PNP transistor Q2, an NPN transistor Q3, a voltage regulator U3, diodes D2 and D3, resistors R4, R5, R6, R7, R8, and R9, and capacitors C5, C6, and C7. In this embodiment, the voltage regulator U3 is a controllable precision voltage regulator TL431. The COMP pin of the control chip U2 is grounded through resistors R6 and R8 connected in series. Capacitor C5 is connected in parallel across resistor R8. The junction between resistors R6 and R8 is connected to the reference terminal of the voltage regulator U3. The +24V DC voltage is connected to the emitter of the PNP transistor Q2 and simultaneously connected to the cathode of the voltage regulator U3 through resistors R4 and R5. The base of the PNP transistor Q2 is connected to the anode of diode D2. The cathode of diode D2 is connected to the junction between resistors R4 and R5. The anode of the voltage regulator U3 is grounded. The collector of PNP transistor Q2 is grounded through resistor R9. Capacitor C6 is connected in parallel across resistor R9. The collector of PNP transistor Q2 is also connected to the anode of diode D3. The cathode of diode D3 is connected to one end of resistor R7 and capacitor C7. The other end of resistor R7 is connected to the base of NPN transistor Q3. The other end of capacitor C7 is grounded. The emitter of NPN transistor Q3 is grounded. The collector serves as the output of the short-circuit detection circuit and is connected to the junction between the base of NPN transistor Q1 in the VCC power supply circuit and the series resistor R3 and capacitor C4. This connection point is named the SCP terminal. This short-circuit detection circuit introduces the signal from the COMP pin of the control chip U2 into the reference terminal of the voltage regulator U3 as a threshold detection through a voltage divider formed by resistors R6 and R8 connected in series. The voltage regulator U3 has a built-in precision reference source, which can provide an accurate threshold judgment basis for the circuit operation. The structure is simple and easy to use. The voltage value of the COMP pin protection threshold can be adjusted simply by adjusting the resistance values ​​of resistors R6 and R8. The SCP terminal in the VCC power supply circuit is controlled by the cooperation of PNP transistor Q2 and NPN transistor Q3.

[0024] The VFB pin of the control chip U2 is grounded, the VREF pin of the control chip U2 is grounded through capacitor C1, and the OUT pin of the control chip U2 outputs PWM.

[0025] The specific working principle of this short-circuit protection circuit is as follows: When the power supply output circuit is active, the feedback signal Vo_FB decreases sharply. After passing through the opto-isolator U1, the voltage at the COMP pin of the control chip U2 increases rapidly. When the voltage introduced to the reference terminal of the voltage regulator U3 after voltage division by resistors R6 and R8 and filtering by capacitor C5 exceeds the threshold voltage of the voltage regulator U3, the PNP transistor Q2 will be turned on. After the PNP transistor Q2 is turned on, the +24V DC voltage will charge capacitors C6 and C7. When the voltage reaches the threshold for the NPN transistor Q3 to turn on, the NPN transistor Q3 will be turned on, the voltage at the SCP terminal in the VCC power supply circuit will be pulled to 0, the NPN transistor Q1 will be turned off, and the control chip U2 will stop working, turning off the PWM output, thereby turning off the output of the entire power supply circuit. The control chip U2 will enter hiccup mode. The hiccup interval can be adjusted by adjusting the resistance value of resistor R6 and the capacitance values ​​of capacitors C5, C6, and C7. When the output is short-circuited, the output diode will have a short-circuit current. Since the hiccup interval of the control chip U2 can be controlled, the energy during the output short circuit can be kept relatively small. At this time, the short-circuit current of the output rectifier diode will be kept very small, so the short-circuit power consumption of the output rectifier diode is relatively low, and its temperature rise is kept relatively low. Long-term short circuit will not cause damage to the output rectifier diode.

[0026] The above embodiments are only used to illustrate the technical solutions of this utility model, and are not intended to limit it. Although this utility model has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this utility model.

Claims

1. A short circuit protection circuit, characterized by: The short circuit detection circuit includes PNP transistor Q2, NPN transistor Q3, voltage stabilizer U3, diode D2, resistor R6 and resistor R8. The COMP pin of the control chip U2 is connected to the ground through the series connection of resistor R6 and resistor R8. The joint between the series connection of resistor R6 and resistor R8 is connected to the reference terminal of the voltage stabilizer U3. The direct current voltage is connected to the emitter of the PNP transistor Q2 and at the same time connected to the cathode of the voltage stabilizer U3 through a resistor. The base of the PNP transistor Q2 is connected to the anode of the diode D2. The cathode of the diode D2 is connected to the cathode of the voltage stabilizer U3. The anode of the voltage stabilizer U3 is connected to the ground. The collector of the PNP transistor Q2 is connected to the ground and the anode of the diode D3 at the same time. The cathode of the diode D3 is connected to the base of the NPN transistor Q3. The emitter of the NPN transistor Q3 is connected to the ground. The collector of the NPN transistor Q3 is connected to the output of the short circuit detection circuit and the VCC power supply circuit for controlling the on-off of the VCC power supply circuit.

2. A short circuit protection circuit as claimed in claim 1, characterized in that: The VCC power supply circuit includes NPN transistor Q1, voltage stabilizer diode D1, resistor R3, capacitor C3 and capacitor C4. The collector of the NPN transistor Q1 is connected to the direct current voltage. The direct current voltage is connected to the ground through the series connection of resistor R3 and capacitor C4 at the same time. The base of the NPN transistor Q1 is connected to the cathode of the voltage stabilizer diode D1. The anode of the voltage stabilizer diode D1 is connected to the ground. The emitter of the NPN transistor Q1 is connected to the VCC pin of the control chip U2 and connected to the ground through the capacitor C3 at the same time. The collector of the NPN transistor Q3 is connected to the base of the NPN transistor Q1 and the joint between the series connection of resistor R3 and capacitor C4 in the VCC power supply circuit.

3. A short circuit protection circuit as claimed in claim 1, characterized in that: The short circuit detection circuit further includes capacitor C5 which is connected in parallel to the resistor R8.

4. A short circuit protection circuit as claimed in claim 3, characterized in that: The short circuit detection circuit further includes resistor R9 and capacitor C6. The collector of the PNP transistor Q2 is connected to the ground through the resistor R9. The capacitor C6 is connected in parallel to the resistor R9.

5. A short circuit protection circuit as claimed in claim 4, characterized in that: The short circuit detection circuit further includes resistor R7 and capacitor C7. The cathode of the diode D3 is connected to one end of the resistor R7 and the capacitor C7. The other end of the resistor R7 is connected to the base of the NPN transistor Q3. The other end of the capacitor C7 is connected to the ground.

6. A short circuit protection circuit as defined in claim 1, characterized in that The short circuit detection circuit further includes resistor R4 and resistor R5. The direct current voltage is connected to the cathode of the voltage stabilizer U3 through the series connection of resistor R4 and R5. The cathode of the diode D2 is connected to the joint between the series connection of resistor R4 and R5.

7. A short circuit protection circuit as defined in claim 1, characterized in that The output voltage feedback circuit is further connected to the COMP pin of the control chip U2.

8. A short circuit protection circuit as claimed in claim 7, characterized in that: The output voltage feedback circuit includes optoelectronic isolator U1, resistor R1, resistor R2 and capacitor C2. The input anode of the optoelectronic isolator U1 is connected to the output voltage +Vo through the resistor R1. The input cathode of the optoelectronic isolator U1 is connected to the output voltage feedback signal Vo_FB. The resistor R2 is connected between the input anode and the input cathode of the optoelectronic isolator U1. The output collector of the optoelectronic isolator U1 is connected to the COMP pin of the control chip U2. The output emitter of the optoelectronic isolator U1 is connected to the ground. The capacitor C2 is connected in parallel between the output collector and the output emitter of the optoelectronic isolator U1.

9. A short circuit protection circuit as defined in claim 1, characterized in that: The voltage stabilizer U3 is a controllable precision voltage stabilizer TL431.

10. A switching power supply control device employing the short-circuit protection circuit according to any one of claims 1 to 9, characterized by: The short circuit protection circuit is connected to the control chip U2.

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