CN116828665A - A kind of constant voltage dimming power supply output short circuit protection circuit - Google Patents

Abstract

The invention provides a constant voltage dimming circuit, which is electrically connected with an LED load and comprises: constant pressure source: for providing power to the LED load; a first switching circuit: controlling the on-off state of the first switch circuit according to the voltage value of the control signal; a second switching circuit: the switching device is used for controlling the on-off of the first switching circuit according to the on-off of the first switching circuit, and the second switching circuit is continuously turned on after being turned on until the preset condition is met; dimming driving circuit: the LED load dimming circuit comprises a switching tube connected with an LED load, wherein a driving signal is used for realizing dimming of the LED load through on-off of the switching tube, and the driving signal is controlled to be in a low level to keep the switching tube and the LED load disconnected according to the on-off state between the driving signal and the switching tube of a second switching circuit when the second switching circuit is conducted. The invention is provided with multiple sensitive protection circuits, has the functions of overload output and short-circuit protection, and can timely protect the circuits after overload and short-circuit, and has the advantages of simple structure, reliable performance, safe use and wide applicability.

Description

A kind of constant voltage dimming power supply output short circuit protection circuit

Technical field

The invention relates to the technical field of electronic circuits, and in particular to a constant voltage dimming circuit with an output short-circuit protection function.

Background technique

LED power supplies currently on the market are generally divided into two categories: constant voltage power supplies and constant current power supplies. In the constant voltage power supply scheme, because the output voltage is constant, the output current will change according to the size of the load. Therefore, when the constant voltage power supply fails, When a short circuit occurs, the output current of the constant voltage power supply will surge in a short period of time.

The current dimming scheme used in constant voltage power supplies is usually implemented by connecting MOSFETs in series on the main circuit for chopping. When the power supply output is short-circuited, there will be a large short-circuit current. In high-power applications, MOSFETs connected in series often have to withstand pulse currents of more than 100A during instantaneous short-circuit, which can easily cause stress damage to the dimming MOSFET. Without a short-circuit protection circuit, it is necessary Choose a highly stressed, expensive MOSFET.

Therefore, those skilled in the art are committed to developing a constant voltage dimming circuit to provide safer protection for the circuit when the load is abnormal.

Contents of the invention

In view of the above-mentioned defects of the prior art, the technical problem to be solved by the present invention is the problem of circuit component damage caused by instantaneous short circuit in the existing constant voltage dimming power supply in high-power applications.

In order to achieve the above object, the present invention provides a constant voltage dimming circuit electrically connected to an LED load, which includes:

Constant voltage source: used to provide power to the LED load;

The first switch circuit: includes a first switch, the first switch is connected to a control signal, and controls the on-off state of the first switch circuit according to the voltage value of the control signal;

Second switch circuit: It is connected to the first switch circuit and used to control its own on-off according to the on-off of the first switch circuit. It includes a second switch. The control pole of the second switch is connected to the first switch circuit. When the second switch circuit After it is turned on, it will continue to turn on until it turns off when the preset conditions are met;

Dimming drive circuit: It is connected to the second switch circuit, including a switch tube connected to the LED load. The drive signal is connected to the control electrode of the switch tube through the drive module. The LED load is dimmed by turning on and off the switch tube. According to the second switch The on-off state of the circuit controls the on-off state between the drive signal and the switch tube. When the second switch circuit is turned on, the drive signal is at a low level to keep the switch tube and the LED load disconnected.

Furthermore, the preset condition is: the output voltage of the first switch circuit is less than the conduction threshold of the second switch circuit.

In one embodiment of the present invention, the first switch circuit also includes a first resistor, a second resistor and a seventh resistor. The first resistor is connected between the working power supply and the input pole of the first switch, and the second resistor is connected between the control Between the signal and the control electrode of the first switch, one end of the seventh resistor is connected to the ground, and the other end is connected to the output electrode of the first switch. The output electrode of the first switch is connected to the control electrode of the second switch.

Preferably, the first switch is turned on when the control electrode receives a low level.

Further, the first switch circuit further includes a filter capacitor, and the filter capacitor is connected in parallel to both ends of the seventh resistor.

In one embodiment of the present invention, the second switch is a one-way thyristor. The second switch circuit also includes a third resistor. The anode of the one-way thyristor is connected in series with the third resistor and is connected to the constant voltage source. The one-way thyristor is connected to the constant voltage source. The cathode of the silicon-controlled thyristor is connected to the ground, and the control electrode of the unidirectional silicon-controlled rectifier is connected to the output terminal of the first switching circuit.

Preferably, the second switch circuit also includes a diode, the anode of the diode is connected to the drive signal, and the cathode of the diode is connected between the unidirectional thyristor and the third resistor. When the second switch circuit is disconnected, the diode isolates the constant voltage source and the drive signal. Signal.

In one embodiment of the present invention, the driving module includes a push-pull circuit composed of a transistor Q3, a transistor Q4, a fourth resistor, and a fifth resistor. The transistor Q3 is an NPN transistor, the transistor Q4 is a PNP transistor, and the transistor Q3 The common connection end of the base of the transistor Q4 is connected to the driving power supply, the emitter of the transistor Q3 is connected to the emitter of the transistor Q4, and the collector of the transistor Q3 is connected to the common connection end of the constant voltage source and the LED load through the fourth resistor. The collector of Q4 is grounded, and the common connection end of the emitters of transistor Q3 and transistor Q4 is connected to the control electrode of the switch tube through a fifth resistor.

Further, the switching tube is a MOS tube Q5, and a sixth resistor R6 is connected in parallel between the gate and the source of the MOS tube Q5.

In a preferred embodiment of the present invention, it also includes a current detection circuit connected to the dimming drive circuit for collecting the current value in the dimming drive circuit and outputting a high level or a low level according to the collected current value. level to the first switch.

Furthermore, the current detection circuit includes an eighth resistor, a thirteenth resistor and a comparator. One end of the eighth resistor is connected to ground and the other end is connected to the switch tube. The first input pin of the comparator is connected to the reference voltage, and the second input pin is connected to the reference voltage. The thirteenth resistor is connected in series between the eighth resistor and the switch tube. The current detection circuit collects the current value of the dimming drive circuit and converts it into a voltage value. After comparison by the comparator, it provides a control signal to the first switch circuit.

The constant voltage dimming circuit of the present invention is equipped with multiple sensitive protection circuits. Through the cascade connection of the first switch circuit and the second switch circuit, it receives a specific control signal to start working when a short circuit occurs. It has a simple structure, reliable performance, safe use and applicable It has a wide range of properties; it has output overload and short-circuit protection. It shuts off the output after overload and short-circuit, which can protect the circuit in time.

The concept, specific structure and technical effects of the present invention will be further described below in conjunction with the accompanying drawings to fully understand the purpose, features and effects of the present invention.

Description of the drawings

Figure 1 is a schematic structural diagram of the constant voltage dimming circuit of the present invention.

Figure 2 is a circuit principle diagram of the constant voltage dimming circuit of the present invention.

Among them: 1 first switch circuit, 11 first switch, 2 second switch circuit, 21 second switch, 3 dimming drive circuit, 31 switch tube, 32 drive module, 33 drive signal, 4 LED load, 5 current detection circuit, 6 constant voltage sources, 7 control signals, and 8 working power supplies.

Detailed ways

In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments These are some embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without making creative efforts fall within the scope of protection of the present invention.

The technical features involved in different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

Example 1

Figure 1 shows a schematic structural diagram of the constant voltage dimming circuit of the present invention. It consists of: a constant voltage source 6, a first switch circuit 1, a second switch circuit 2 and a dimming drive circuit 3. The dimming drive circuit 3 is connected to the LED load 4 and dimes the LED load 4.

The constant voltage source 6 is connected to the LED load 4 for providing power to the LED load 4; the first switch circuit 1 includes a first switch 11, and the first switch 11 is connected to the control signal 7. The control signal 7 is controlled according to the state of the dimming drive circuit 3. Trigger changes, such as continuously outputting high level or low level during a short circuit, and controlling the on-off state of the first switch circuit 1 according to the voltage value of the control signal 7. In the embodiment of the present invention, when a short circuit occurs, a specific The control signal 7 is input to the first switch 11 to turn on the first switch 11 and output a high level.

The second switch circuit 2 is connected to the first switch circuit 1 and is used to control its own on-off according to the on-off of the first switch circuit 1. It includes a second switch 21. The control pole of the second switch 21 is connected to the first switch circuit 1. When After the second switch circuit 2 is turned on, it will continue to be turned on until the preset conditions are met and then turned off. Specifically, in one embodiment, the preset condition is: the output voltage of the first switch circuit 1 is less than the conduction threshold of the second switch circuit 2 . After the first switch circuit 1 is turned on, when its output voltage reaches or exceeds the turn-on threshold of the second switch circuit 2, the second switch circuit 2 turns on and remains turned on until the output voltage of the first switch circuit 1 That is, when the input voltage of the second switch 21 is less than its conduction threshold, the second switch circuit 2 is turned off.

Accordingly, through the cascade connection of the first switch circuit 1 and the second switch circuit 2, the specific control signal 7 input will be turned on when a short circuit occurs, and will always be turned on as long as there is a continuous control signal 7.

The dimming drive circuit 3 is connected to the second switch circuit 2 and includes a switch tube 31 connected to the LED load 4. The drive signal 33 is input to the control electrode of the switch tube 31 through the drive module 32, and the LED load is controlled by turning on and off the switch tube 31. 4 dimming, the on-off state between the drive signal 33 and the switch tube 31 is controlled according to the on-off of the second switch circuit 2. When the second switch circuit 2 is turned on, the drive signal 33 is made low level and the switch tube 31 and LED load 4 remain disconnected. Further, the driving signal 33 is a PWM signal or an analog signal or other common dimming signal in this field. Specifically, in one embodiment, when the circuit current is normal, the second switch circuit 2 is turned off, and the drive signal 33 is a normal dimming signal to cause normal operation between the switch tube 31 and the LED load; when a short circuit condition occurs, the input The control signal 7 goes to the first switch circuit 1 and turns on the second switch circuit 2, keeping the drive signal 33 at a low level, keeping the switch tube 31 and the LED load 4 disconnected, and the LED load 4 does not work, so that the Short circuit protection is implemented.

Furthermore, the constant voltage dimming circuit of the present invention also includes a current detection circuit 5, and the control signal 7 is fed back to the first switch circuit 1 through the current detection circuit 5. The current detection circuit 5 is connected to the dimming drive circuit 3 for collecting the current value in the dimming drive circuit 3 and outputting a high level or a low level to the first switch 11 according to the collected current value, that is, the control signal 7 . In one embodiment, the dimming drive circuit 3 outputs different high and low voltage control signals 7 to the first switch circuit 1 through the current detection circuit 5 during normal operation and short circuit abnormality.

Example 2

Figure 2 shows the circuit principle diagram of the constant voltage dimming circuit of the present invention. The constant voltage dimming circuit includes in sequence: a constant voltage source 6, a first switch circuit 1, a second switch circuit 2 and a dimming drive circuit 3. The dimming drive circuit 3 is connected to the LED load 4 and dims the LED load 4. The dimming The drive circuit 3 is connected to the current detection circuit 5 , and the current detection circuit 5 collects the current value in the dimming drive circuit 3 and feeds back the control signal 7 to the first switch circuit 1 .

Specifically, the first switch circuit 1 includes: a first switch 11, a first resistor R1, a second resistor R2, and a seventh resistor R7. The first resistor R1 is connected between the working power supply 8 and the input electrode of the first switch 11, the second resistor R2 is connected between the control signal 7 and the control electrode of the first switch 11, one end of the seventh resistor R7 is grounded, and the other end The output pole of the first switch 11 is connected to the control pole of the second switch 21 .

In the embodiment shown in FIG. 2 , the first switch 11 is configured to be turned on when the control electrode receives a low level. Accordingly, the first switch 11 can be a PMOS transistor or a PNP transistor. Preferably, the first switch 11 is a PNP transistor Q1. The first switch circuit 1 also includes a first resistor R1, a second resistor R2 and a seventh resistor R7. The first resistor R1 is connected between the working power supply 8 and the PNP transistor Q1. Between the emitters, the second resistor R2 is connected between the control signal 7 and the base of the PNP transistor Q1. One end of the seventh resistor R7 is connected to ground, and the other end is connected to the collector of the PNP transistor Q1. The collector of the PNP transistor Q1 The electrode is connected to the control electrode of unidirectional thyristor Q2.

Preferably, the first switch circuit 1 further includes a filter capacitor C1, and the filter capacitor C1 is connected in parallel to both ends of the seventh resistor R7. In this way, the output signal of the first switch circuit 1 is filtered and then input to the second switch circuit 2 .

As shown in Figure 2, the second switch circuit 2 includes: a unidirectional thyristor Q2, a third resistor R3 and a diode D3. The anode of the unidirectional thyristor Q2 is connected in series with the third resistor R3 and then connected to the constant voltage source 6. The cathode of the unidirectional thyristor Q2 is connected to the ground. The control electrode of the unidirectional thyristor Q2 is connected to the output end of the first switching circuit 1. . The anode of the diode D3 is connected to the drive signal 33 of the dimming drive circuit 3, and the cathode of the diode D3 is connected between the unidirectional thyristor Q2 and the third resistor R3.

The second switch circuit 2 makes use of the characteristic that once the unidirectional thyristor Q2 is turned on, it can only be turned off by removing the load or reducing the voltage at both ends to ensure that after the current overload or short circuit causes the second switch circuit 2 to be turned on, only The current can be restored only after the fault is eliminated or restarted to bring the current within the normal range, which improves the safety of the circuit.

At the same time, utilizing the unidirectional conduction characteristics of diode D3, when the unidirectional thyristor Q2 is turned on, the driving signal 33 is connected to the ground through the diode D3 and the unidirectional thyristor Q2. When the unidirectional thyristor Q2 is turned off, the third The second switch circuit 2 and the dimming drive circuit 3 are kept disconnected, while isolating the constant voltage source 6 and the drive signal 33. The drive signal 33 is connected to the switch tube 31, and the LED load 4 is dimmed by controlling the switching tube 31 on and off.

Further, the switch transistor 31 is a MOS transistor Q5, preferably an NMOS transistor in this embodiment. The gate of MOS tube Q5 is connected to the driving power supply, the source of MOS tube Q5 is connected to ground, and the drain of MOS tube Q5 is connected to LED load 4. A sixth resistor R6 is connected in parallel between the gate and the source of the MOS tube Q5, which plays a role in GS inter-electrode discharge protection.

In the dimming drive circuit 3, the drive module 32 includes a push-pull circuit composed of a transistor Q3, a transistor Q4, a fourth resistor R4, and a fifth resistor R5. The transistor Q3 is an NPN type transistor, and the transistor Q4 is a PNP type transistor. The common connection end of the base of Q3 and transistor Q4 is connected to the driving power supply, the emitter of transistor Q3 is connected to the emitter of transistor Q4, and the collector of transistor Q3 is connected to the common terminal of constant voltage source 6 and LED load 4 through the fourth resistor R4. At the connection end, the collector of the transistor Q4 is grounded, and the common connection end of the emitters of the transistor Q3 and the transistor Q4 is connected to the control electrode of the switch tube 31 through the fifth resistor R5. In this way, the driving signal 33 first passes through the push-pull circuit and then is connected to the MOS transistor Q5. The advantage of choosing a push-pull circuit is that it improves the current supply capability in the dimming drive circuit 3 and quickly completes the charging process of the gate input capacitor of the MOS tube Q5. The push-pull circuit reduces the turn-off time, and the MOS tube Q5 can Fast turn-on and avoid high-frequency oscillation on the rising edge.

The current detection circuit 5 includes an eighth resistor R8, a thirteenth resistor R13 and a comparator N1A. One end of the eighth resistor R8 is grounded and the other end is connected to the switch tube 31. The first input pin of the comparator N1A is connected to a reference voltage. The voltage is provided by the working power supply 8 after being divided by resistors R9, R10, and R11. The second input pin is connected in series with the thirteenth resistor R13 and then connected between the eighth resistor R8 and the switch tube 31. The current detection circuit 5 collects the dimming drive The current value of the circuit 3 is converted into a voltage value, and is compared by the comparator N1A to provide the control signal 7 to the first switching circuit 1 . In the embodiment shown in Figure 2, the non-inverting input terminal of the comparator N1A is connected to the reference voltage, and the reverse input terminal is connected to the detected voltage signal. When the current is greater than the set value, the output pin of the comparator N1A outputs a low voltage. level, and outputs high level during normal operation.

In addition, according to the technical solutions in the above embodiments, the constant voltage dimming power supply of the present invention can also have other combination solutions. For example, the first switch 11 is set as an NPN transistor, which is turned on when receiving a high level. Correspondingly, in the current detection circuit 5 , the comparator N1A outputs a high level as the control signal 7 when detecting a current overload or short circuit. Give the first switch 11.

This constant voltage dimming power supply can disconnect the LED load 4 when the current is overloaded or short-circuited to avoid damage to circuit components and improve the safety of the circuit. Its working principle is:

When the dimming drive circuit 3 works normally, its current is within the normal range. The voltage signal taken out by the current detection circuit 5 through the detection resistor, the eighth resistor R8, is less than the set reference voltage. The output pin of the comparator N1A outputs a high level, which The high level is input to the PNP transistor Q1 of the first switch circuit 1 as the control signal 7. The PNP transistor Q1 is turned off and has no output. The second switch circuit 2 is turned off. The diode D3 is cut off and isolates the constant voltage source and the drive signal 33. The drive signal 33 is connected to the switch tube 31 via the drive module 32 to dim the LED load 4;

When the dimming drive circuit 3 is overloaded or short-circuited, the current detection circuit 5 detects that the voltage signal taken out is greater than the set reference voltage, and the output pin of the comparator N1A outputs a low level, which is input to the first switch as the control signal 7 The PNP transistor Q1 of circuit 1 turns on the PNP transistor Q1. After it is turned on, the first resistor R1 and the seventh resistor R7 divide the voltage and output a trigger level to the second switch circuit 2, and the unidirectional thyristor Q2 is turned on. , after the third resistor R3 is turned on, the holding current is provided to the unidirectional thyristor Q2. The driving signal 33 is grounded through the diode D3 and the unidirectional thyristor Q2. At this time, the output of the driving signal 33 continues to be low level, thereby causing the MOS tube Q5 to There is no input to the gate, and LED load 4 does not work;

After the short circuit is eliminated, the circuit is restarted, the locking state of the one-way thyristor Q2 is eliminated, and the current of the dimming drive circuit 3 returns to the normal range. For example, in the normal working state, the first switch circuit 1 and the second switch circuit 2 are turned off, and the drive signal 33 It is turned on and acts on the switch tube 31 to dim the LED load 4.

The preferred embodiments of the present invention are described in detail above. It should be understood that those skilled in the art can make many modifications and changes based on the concept of the present invention without creative efforts. Therefore, any technical solutions that can be obtained by those skilled in the art through logical analysis, reasoning or limited experiments based on the concept of the present invention and on the basis of the prior art should be within the scope of protection determined by the claims.

Claims (11)

1. A constant voltage dimming circuit electrically connected to an LED load (4), comprising:

constant voltage source (6): for supplying power to the LED load (4);

a first switching circuit (1): the circuit comprises a first switch (11), wherein the first switch (11) is connected with a control signal (7), and the on-off state of the first switch circuit (1) is controlled according to the voltage value of the control signal (7);

a second switching circuit (2): the control electrode of the second switch (21) is connected with the first switch circuit (1), and the second switch circuit (2) is continuously conducted until a preset condition is met and then disconnected;

dimming driving circuit (3): the LED dimming circuit is connected with a second switching circuit (2), comprises a switching tube (31) connected with an LED load (4), a driving signal (33) is connected with a control electrode of the switching tube (31) through a driving module (32), dimming of the LED load (4) is achieved through on-off of the switching tube (31), and when the second switching circuit (2) is conducted, the driving signal (33) is made to be in a low level to enable the switching tube (31) and the LED load (4) to be kept disconnected according to the on-off state between the driving signal (33) and the switching tube (31) which are controlled by on-off of the second switching circuit (2).

2. The constant voltage dimming circuit of claim 1, wherein the preset condition is: the output voltage of the first switching circuit (1) is smaller than the conduction threshold of the second switching circuit (2).

3. Constant voltage dimming circuit according to claim 1 or 2, characterized in that the first switching circuit (1) further comprises a first resistor R1, a second resistor R2 and a seventh resistor R7, the first resistor R1 being connected between the operating power supply (8) and the input pole of the first switch (11), the second resistor R2 being connected between the control signal (7) and the control pole of the first switch (11), one end of the seventh resistor R7 being grounded, the other end being connected to the output pole of the first switch (11), the output pole of the first switch (11) being connected to the control pole of the second switch (21).

4. A constant voltage dimming circuit according to claim 3, wherein the first switch (11) is turned on when the control electrode receives a low level.

5. A constant voltage dimming power supply output short-circuit protection circuit as claimed in claim 3, characterized in that the first switching circuit (1) further comprises a filter capacitor C1, the filter capacitor C1 being connected in parallel across the seventh resistor R7.

6. The constant voltage dimming circuit according to claim 1 or 2, wherein the second switch (21) is a unidirectional silicon controlled rectifier Q2, the second switch circuit (2) further comprises a third resistor R3, the anode of the unidirectional silicon controlled rectifier Q2 is connected with the constant voltage source (6) after being connected with the third resistor R3 in series, the cathode of the unidirectional silicon controlled rectifier Q2 is grounded, and the control electrode of the unidirectional silicon controlled rectifier Q2 is connected with the output end of the first switch circuit (1).

7. The constant voltage dimming circuit according to claim 6, wherein the second switching circuit (2) further comprises a diode D3, an anode of the diode D3 is connected to the driving signal (33), a cathode of the diode D3 is connected between the unidirectional thyristor Q2 and the third resistor R3, and the diode D3 isolates the constant voltage source (6) from the driving signal (33) when the second switching circuit (2) is turned off.

8. The constant voltage dimming circuit according to claim 1 or 2, wherein the driving module (32) comprises a push-pull circuit comprising a triode Q3, a triode Q4, a fourth resistor R4 and a fifth resistor R5, wherein the triode Q3 is an NPN triode, the triode Q4 is a PNP triode, the common connection terminal of the bases of the triode Q3 and the triode Q4 is connected with the driving power supply, the emitter of the triode Q3 is connected with the emitter of the triode Q4, the collector of the triode Q3 is connected with the common connection terminal of the constant voltage source (6) and the LED load (4) through the fourth resistor R4, the collector of the triode Q4 is grounded, and the common connection terminal of the emitters of the triode Q3 and the triode Q4 is connected with the control electrode of the switching tube (31) through the fifth resistor R5.

9. The constant voltage dimming circuit as claimed in claim 8, wherein the switching tube (31) is a MOS tube Q5, and a sixth resistor R6 is connected in parallel between the gate and the source of the MOS tube Q5.

10. The constant voltage dimming circuit according to claim 1 or 2, further comprising a current detection circuit (5), wherein the current detection circuit (5) is connected to the dimming driving circuit (3) for collecting a current value in the dimming driving circuit (3) and outputting a high level or a low level to the first switch (11) according to the collected current value.

11. The constant voltage dimming circuit of claim 10, wherein the current detection circuit (5) comprises an eighth resistor R8, a thirteenth resistor R13 and a comparator N1A, one end of the eighth resistor R8 is grounded, the other end of the eighth resistor R8 is connected with the switching tube (31), a first input pin of the comparator N1A is connected with a reference voltage, a second input pin is connected between the eighth resistor R8 and the switching tube (31) after being connected with the thirteenth resistor R13 in series, the current detection circuit (5) collects the current value of the dimming driving circuit (3) and converts the current value into a voltage value, and the voltage value is compared by the comparator N1A to provide the control signal (7) for the first switching circuit (1).