Constant-voltage dimmer power supply output short circuit protection circuit

Abstract

The application provides a constant-voltage dimming circuit, which is electrically connected with an LED load and comprises a constant-voltage source, a first switch circuit, a second switch circuit and a dimming driving circuit, wherein the constant-voltage source is used for providing power supply for the LED load; the first switch circuit is used for controlling the on-off state of the first switch circuit according to the voltage value of a control signal; the second switch circuit is used for controlling its on-off according to the on-off of the first switch circuit, and the second switch circuit is kept on until a preset condition is met and then is turned off; the dimming driving circuit comprises a switch tube connected with the LED load, a driving signal passes through the on-off of the switch tube to realize the dimming of the LED load, and the on-off state between the driving signal and the switch tube is controlled according to the on-off of the second switch circuit; when the second switch circuit is on, the driving signal is low to keep the switch tube and the LED load disconnected. The application is provided with multiple sensitive protection circuits, has output overload and short-circuit protection, turns off the output after overload and short-circuit, can protect the circuit in time, has simple structure, reliable performance, safe use and wide applicability.

Description

Technical Field

[0001] This invention relates to the field of electronic circuit technology, and in particular to a constant voltage dimming circuit with output short-circuit protection function. Background Technology

[0002] Currently, LED power supplies on the market are generally divided into two main categories: constant voltage power supplies and constant current power supplies. In constant voltage power supply solutions, because the output voltage is constant, the output current will vary according to the load size. Therefore, when a constant voltage power supply fails and causes a short circuit, the output current of the constant voltage power supply will surge in a short period of time.

[0003] The dimming scheme currently used in constant voltage power supplies typically involves connecting a MOSFET in series in the main circuit for chopping. When the power supply is short-circuited at the output, there will be a large short-circuit current. In high-power applications, the MOSFET connected in series often has to withstand pulse currents exceeding 100A during a momentary short circuit, which can easily cause stress damage to the dimming MOSFET. Without a short-circuit protection circuit, it would be necessary to use expensive MOSFETs with high stress levels.

[0004] Therefore, those skilled in the art are dedicated to developing a constant voltage dimming circuit that provides greater protection for the circuit under abnormal load conditions. Summary of the Invention

[0005] In view of the above-mentioned deficiencies of the prior art, the technical problem to be solved by the present invention is the damage to circuit components caused by instantaneous short circuits in existing constant voltage dimming power supplies in high-power applications.

[0006] To achieve the above objectives, the present invention provides a constant voltage dimming circuit, electrically connected to an LED load, comprising:

[0007] Constant voltage source: Used to provide power to LED loads;

[0008] First switching circuit: includes a first switch, the first switch is connected to a control signal, and the on / off state of the first switching circuit is controlled according to the voltage value of the control signal;

[0009] Second switching circuit: It is connected to the first switching circuit and is used to control its own on / off state according to the on / off state of the first switching circuit. It includes a second switch, the control electrode of the second switch is connected to the first switching circuit, and when the second switching circuit is turned on, it will continue to be turned on until the preset condition is met and then it will be turned off.

[0010] Dimming drive circuit: It is connected to the second switching circuit, including a switching transistor connected to the LED load. The drive signal is connected to the control electrode of the switching transistor through the drive module. The dimming of the LED load is realized by switching the switching transistor on and off. The on and off state between the drive signal and the switching transistor is controlled according to the on and off state of the second switching circuit. When the second switching circuit is on, the drive signal is low to keep the switching transistor and the LED load disconnected.

[0011] Furthermore, the preset condition is: the output voltage of the first switching circuit is less than the conduction threshold of the second switching circuit.

[0012] In one embodiment of the present invention, the first switching circuit further includes a first resistor, a second resistor, and a seventh resistor. The first resistor is connected between the operating power supply and the input terminal of the first switch, the second resistor is connected between the control signal and the control terminal of the first switch, one end of the seventh resistor is grounded, and the other end is connected to the output terminal of the first switch. The output terminal of the first switch and the control terminal of the second switch are connected together.

[0013] Preferably, the first switch is turned on when the control electrode receives a low level.

[0014] Furthermore, the first switching circuit also includes a filter capacitor, which is connected in parallel across the seventh resistor.

[0015] In one embodiment of the present invention, the second switch is a unidirectional thyristor, and the second switch circuit further includes a third resistor. The anode of the unidirectional thyristor is connected in series with the third resistor and then connected to a constant voltage source. The cathode of the unidirectional thyristor is grounded, and the control electrode of the unidirectional thyristor is connected to the output terminal of the first switch circuit.

[0016] Preferably, the second switching circuit further includes a diode, the anode of which is connected to the drive signal, and the cathode of which is connected between the unidirectional thyristor and the third resistor. When the second switching circuit is turned off, the diode isolates the constant voltage source and the drive signal.

[0017] In one embodiment of the present invention, the driving module includes a push-pull circuit composed of transistor Q3, transistor Q4, a fourth resistor, and a fifth resistor. Transistor Q3 is an NPN transistor, and transistor Q4 is a PNP transistor. The common connection terminal of the bases of transistors Q3 and Q4 is connected to the driving power supply. The emitter of transistor Q3 is connected to the emitter of transistor Q4. The collector of transistor Q3 is connected to the common connection terminal of the constant voltage source and the LED load via the fourth resistor. The collector of transistor Q4 is grounded. The common connection terminal of the emitters of transistors Q3 and Q4 is connected to the control terminal of the switching transistor via the fifth resistor.

[0018] Furthermore, the switching transistor is a MOSFET Q5, and a sixth resistor R6 is connected in parallel between the gate and source of the MOSFET Q5.

[0019] In a preferred embodiment of the present invention, a current detection circuit is further included. The current detection circuit is connected to the dimming drive circuit and is used to collect the current value in the dimming drive circuit, and output a high level or low level to the first switch according to the collected current value.

[0020] Furthermore, the current detection circuit includes an eighth resistor, a thirteenth resistor, and a comparator. One end of the eighth resistor is grounded and the other end is connected to the switching transistor. The first input pin of the comparator is connected to a reference voltage, and the second input pin is connected between the eighth resistor and the switching transistor after being connected in series with the thirteenth resistor. 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 switching circuit.

[0021] The constant voltage dimming circuit of the present invention is equipped with multiple sensitive protection circuits. Through the cascading of the first and second switching circuits, it receives a specific control signal to start working when a short circuit occurs. It has a simple structure, reliable performance, safe use, and wide applicability. It has output overload and short circuit protection, and shuts off the output after overload and short circuit, which can protect the circuit in time.

[0022] The following will further explain the concept, specific structure, and technical effects of the present invention in conjunction with the accompanying drawings, so as to fully understand the purpose, features, and effects of the present invention. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the constant voltage dimming circuit of the present invention.

[0024] Figure 2 This is a circuit diagram of the constant voltage dimming circuit of the present invention.

[0025] The components are: 1 first switch circuit, 11 first switch, 2 second switch circuit, 21 second switch, 3 dimming drive circuit, 31 switching transistor, 32 drive module, 33 drive signal, 4 LED load, 5 current detection circuit, 6 constant voltage source, 7 control signal, and 8 working power supply. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0027] The technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0028] Example 1

[0029] like Figure 1 The diagram shows the structure of the constant voltage dimming circuit of the present invention. It consists of: a constant voltage source 6, a first switching circuit 1, a second switching 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.

[0030] A constant voltage source 6 is connected to an LED load 4 to provide power to the LED load 4. The first switching circuit 1 includes a first switch 11, which is connected to a control signal 7. The control signal 7 is triggered and changed according to the state of the dimming drive circuit 3, for example, continuously outputting a high level or a low level when there is a short circuit. The on / off state of the first switching circuit 1 is controlled according to the voltage value of the control signal 7. In an embodiment of the present invention, when a short circuit occurs, a specific control signal 7 is input to the first switch 11 to make the first switch 11 conduct and output a high level.

[0031] The second switching circuit 2 is connected to the first switching circuit 1 and is used to control its own on / off state according to the on / off state of the first switching circuit 1. It includes a second switch 21, the control electrode of which is connected to the first switching circuit 1. When the second switching circuit 2 is turned on, it remains on until a preset condition is met, at which point it is turned off. Specifically, in one embodiment, the preset condition is that the output voltage of the first switching circuit 1 is less than the on-threshold of the second switching circuit 2. After the first switching circuit 1 is turned on, when its output voltage reaches or exceeds the on-threshold of the second switching circuit 2, the second switching circuit 2 is turned on and remains on until the output voltage of the first switching circuit 1, which is also the input voltage of the second switch 21, is less than its on-threshold, at which point the second switching circuit 2 is turned off.

[0032] Accordingly, by cascading the first switching circuit 1 and the second switching circuit 2, a specific control signal 7 will be input and conduct when a short circuit occurs, and will continue to conduct as long as there is a continuous control signal 7.

[0033] The dimming drive circuit 3 is connected to the second switching circuit 2 and includes a switching transistor 31 connected to the LED load 4. A drive signal 33 is input to the control electrode of the switching transistor 31 via the drive module 32. Dimming of the LED load 4 is achieved by switching the transistor 31 on and off. The on / off state between the drive signal 33 and the switching transistor 31 is controlled according to the on / off state of the second switching circuit 2. When the second switching circuit 2 is on, the drive signal 33 is at a low level, keeping the switching transistor 31 and the LED load 4 disconnected. Further, the drive signal 33 is a PWM signal or an analog signal, or other dimming signals commonly used in the art. Specifically, in one embodiment, when the circuit current is normal, the second switching circuit 2 is off, and the drive signal 33 is a normal dimming signal, allowing the switching transistor 31 and the LED load to operate normally. When a short circuit occurs, a control signal 7 is input to the first switching circuit 1, and the second switching circuit 2 is turned on, keeping the drive signal 33 at a low level, keeping the switching transistor 31 and the LED load 4 disconnected. The LED load 4 does not work, thus achieving timely short-circuit protection.

[0034] 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 switching circuit 1 via the current detection circuit 5. The current detection circuit 5 is connected to the dimming drive circuit 3 and is used to collect the current value in the dimming drive circuit 3, and output a high level or low level to the first switch 11, i.e., the control signal 7, according to the collected current value. In one embodiment, the dimming drive circuit 3 outputs different high and low voltage control signals 7 to the first switching circuit 1 through the current detection circuit 5 during normal operation and short circuit abnormality.

[0035] Example 2

[0036] like Figure 2 The diagram shows the circuit principle 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 switching circuit 1, a second switching 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 drive circuit 3 is connected to the current detection circuit 5, which collects the current value in the dimming drive circuit 3 and feeds back the control signal 7 to the first switching circuit 1.

[0037] Specifically, the first switching 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 operating power supply 8 and the input terminal of the first switch 11, the second resistor R2 is connected between the control signal 7 and the control terminal of the first switch 11, one end of the seventh resistor R7 is grounded, and the other end is connected to the output terminal of the first switch 11. The output terminal of the first switch 11 is connected to the control terminal of the second switch 21.

[0038] In such Figure 2In the illustrated embodiment, the first switch 11 is configured to turn 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 further includes a first resistor R1, a second resistor R2, and a seventh resistor R7. The first resistor R1 is connected between the operating power supply 8 and the emitter of the PNP transistor Q1. 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 grounded, and the other end is connected to the collector of the PNP transistor Q1. The collector of the PNP transistor Q1 is connected to the control electrode of the unidirectional thyristor Q2.

[0039] Preferably, the first switching circuit 1 further includes a filter capacitor C1, which is connected in parallel across the seventh resistor R7. In this way, the output signal of the first switching circuit 1 is filtered before being input to the second switching circuit 2.

[0040] like Figure 2 As shown, the second switching 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 grounded, and the control electrode of the unidirectional thyristor Q2 is connected to the output terminal 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.

[0041] The second switching circuit 2 utilizes 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 across its terminals. This ensures that if the second switching circuit 2 is turned on due to current overload or short circuit, it can only be restored after the fault is cleared or the current is restarted and brought back to the normal range, thus improving the safety of the circuit.

[0042] Meanwhile, taking advantage of the unidirectional conduction characteristic of diode D3, when unidirectional thyristor Q2 is turned on, the drive signal 33 is grounded after passing through diode D3 and unidirectional thyristor Q2. When unidirectional thyristor Q2 is turned off, the second switching circuit 2 and the dimming drive circuit 3 remain disconnected, while isolating the constant voltage source 6 and the drive signal 33. The drive signal 33 is connected to the switching transistor 31, and the LED load 4 is dimmed by controlling the on and off of the switching transistor 31.

[0043] Furthermore, the switching transistor 31 is a MOSFET Q5, preferably an NMOS transistor in this embodiment. The gate of the MOSFET Q5 is connected to the driving power supply, the source of the MOSFET Q5 is grounded, and the drain of the MOSFET is connected to the LED load 4. A sixth resistor R6 is connected in parallel between the gate and source of the MOSFET Q5 to provide gate-source discharge protection.

[0044] In the dimming drive circuit 3, the drive module 32 includes a push-pull circuit composed of transistors Q3 and Q4, a fourth resistor R4, and a fifth resistor R5. Transistor Q3 is an NPN transistor, and transistor Q4 is a PNP transistor. The common connection terminal of the bases of transistors Q3 and Q4 is connected to the drive power supply. The emitter of transistor Q3 is connected to the emitter of transistor Q4. The collector of transistor Q3 is connected to the common connection terminal of the constant voltage source 6 and the LED load 4 via the fourth resistor R4. The collector of transistor Q4 is grounded. The common connection terminal of the emitters of transistors Q3 and Q4 is connected to the control terminal of the switching transistor 31 via the fifth resistor R5. Thus, the drive signal 33 first passes through the push-pull circuit before being connected to the MOSFET Q5. The advantage of using a push-pull circuit is that it improves the current supply capability of the dimming drive circuit 3, quickly completes the charging process of the gate input capacitor of MOSFET Q5, reduces the turn-off time, and enables MOSFET Q5 to turn on quickly and avoids high-frequency oscillation of the rising edge.

[0045] 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 switching transistor 31. The first input pin of the comparator N1A is connected to a reference voltage, which is provided by the operating power supply 8 through a voltage divider formed by resistors R9, R10, and R11. The second input pin is connected in series with the thirteenth resistor R13 and then between the eighth resistor R8 and the switching transistor 31. The current detection circuit 5 acquires the current value of the dimming drive circuit 3, converts it into a voltage value, and provides a control signal 7 to the first switching circuit 1 after comparison by the comparator N1A. Figure 2 In the embodiment shown, the non-inverting input of comparator N1A is connected to a reference voltage, and the inverting input is connected to a detected voltage signal. When the current is greater than a set value, the output pin of comparator N1A outputs a low level, while it outputs a high level during normal operation.

[0046] Furthermore, based on the technical solutions in the above embodiments, the constant voltage dimming power supply of the present invention can also have other combination schemes. For example, the first switch 11 is set as an NPN transistor, which conducts when it receives a high level. Correspondingly, in the current detection circuit 5, the comparator N1A outputs a high level as a control signal 7 to the first switch 11 when it detects a current overload or short circuit.

[0047] This constant voltage dimming power supply can disconnect the LED load 4 in case of current overload or short circuit, preventing damage to circuit components and improving circuit safety. Its working principle is as follows:

[0048] When the dimming drive circuit 3 is working normally, its current is within the normal range. The voltage signal taken by the current detection circuit 5 through the detection resistor, i.e. the eighth resistor R8, is less than the set reference voltage. The output pin of the comparator N1A outputs a high level. This high level is used as the control signal 7 and input to the PNP transistor Q1 of the first switching circuit 1. The PNP transistor Q1 is turned off and has no output. The second switching 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 switching transistor 31 through the drive module 32 to dim the LED load 4.

[0049] When the dimming drive circuit 3 is overloaded or short-circuited, the current detection circuit 5 detects that the voltage signal is greater than the set reference voltage. The comparator N1A outputs a low level, which is used as a control signal 7 to input to the PNP transistor Q1 of the first switching circuit 1, turning on the PNP transistor Q1. After it turns on, the first resistor R1 and the seventh resistor R7 divide the voltage and output a trigger level to the second switching circuit 2, turning on the unidirectional thyristor Q2. After it turns on, the third resistor R3 provides a sustaining current to the unidirectional thyristor Q2. The drive signal 33 is grounded through the diode D3 and the unidirectional thyristor Q2. At this time, the drive signal 33 outputs a continuous low level, so that the gate of the MOSFET Q5 has no input and the LED load 4 does not work.

[0050] After the short circuit is eliminated, the circuit restarts. The locked state of the unidirectional thyristor Q2 is eliminated, and the current of the dimming drive circuit 3 returns to the normal range. In normal working condition, the first switch circuit 1 and the second switch circuit 2 are turned off, and the drive signal 33 is turned on and acts on the switch tube 31 to dim the LED load 4.

[0051] The preferred embodiments of the present invention have been described in detail above. It should be understood that those skilled in the art can make numerous modifications and variations based on the concept of the present invention without creative effort. Therefore, all technical solutions that can be obtained by those skilled in the art based on the concept of the present invention through logical analysis, reasoning, or limited experimentation on the basis of existing technology should be within the scope of protection defined by the claims.

Claims

1. A constant voltage dimming power supply output short-circuit protection circuit, electrically connected to an LED load (4), characterized in that, include: Constant voltage source (6): used to provide power to the LED load (4); Dimming drive circuit (3): It is connected to constant voltage source (6), second switching circuit (2) and LED load (4) respectively; The current detection circuit (5) is connected to the dimming drive circuit (3) to collect the current value in the dimming drive circuit (3) and convert it into a voltage value. After comparison by the comparator (N1A), it provides a control signal (7) to the first switching circuit (1). The control signal is either high level or low level. First switch circuit (1): includes first switch (11), the first switch is a PNP transistor (Q1), the first switch (11) receives control signal (7), and controls the on / off state of the first switch circuit (1) according to the voltage value of control signal (7). The first switch (11) is turned on when the control electrode receives a low level. The second switching circuit (2) is connected to the first switching circuit (1) and is used to control its own on / off state according to the on / off state of the first switching circuit (1). It includes a second switch (21), which is a unidirectional thyristor (Q2). The control electrode of the second switch (21) is connected to the first switching circuit (1). When the second switching circuit (2) is turned on, it will continue to be turned on until the preset condition is met and then it will be turned off. The preset condition is: the output voltage of the first switching circuit (1) is less than the on-threshold of the second switching circuit (2). The dimming drive circuit (3) includes a switch (31) connected to the LED load (4). The drive signal (33) is connected to the control electrode of the switch (31) via the drive module (32). The dimming of the LED load (4) is achieved by switching the switch (31) on and off. The on and off state between the drive signal (33) and the switch (31) is controlled by the on and off state of the second switch circuit (2). When the second switch circuit (2) is on, the drive signal (33) is at a low level, keeping the switch (31) and the LED load (4) disconnected.

2. The constant voltage dimming power supply output short-circuit protection circuit as described in claim 1, characterized in that, 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 input terminal of the first switch (11). The second resistor R2 is connected between the control signal (7) and the control terminal of the first switch (11). One end of the seventh resistor R7 is grounded and the other end is connected to the output terminal of the first switch (11). The output terminal of the first switch (11) is connected to the control terminal of the second switch (21).

3. The constant voltage dimming power supply output short-circuit protection circuit as described in claim 2, characterized in that, The first switching circuit (1) also includes a filter capacitor C1, which is connected in parallel across the seventh resistor R7.

4. The constant voltage dimming power supply output short-circuit protection circuit as described in claim 1, characterized in that, The second switching circuit (2) also includes a third resistor R3. 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 grounded, and the control electrode of the unidirectional thyristor Q2 is connected to the output terminal of the first switching circuit (1).

5. The constant voltage dimming power supply output short-circuit protection circuit as described in claim 4, characterized in that, The second switching circuit (2) also includes a diode D3. The anode of the diode D3 is connected to the drive signal (33), and the cathode of the diode D3 is connected between the unidirectional thyristor Q2 and the third resistor R3. When the second switching circuit (2) is turned off, the diode D3 isolates the constant voltage source (6) and the drive signal (33).

6. The constant voltage dimming power supply output short-circuit protection circuit as described in claim 1, characterized in that, The driving module (32) includes a push-pull circuit composed of transistor Q3, transistor Q4, fourth resistor R4 and fifth resistor R5. Transistor Q3 is an NPN transistor and transistor Q4 is a PNP transistor. The common connection terminal of the bases of transistors Q3 and Q4 is connected to the driving power supply. The emitter of transistor Q3 is connected to the emitter of transistor Q4. The collector of transistor Q3 is connected to the common connection terminal of constant voltage source (6) and LED load (4) through the fourth resistor R4. The collector of transistor Q4 is grounded. The common connection terminal of the emitters of transistors Q3 and Q4 is connected to the control terminal of switching transistor (31) through the fifth resistor R5.

7. The constant voltage dimming power supply output short-circuit protection circuit as described in claim 6, characterized in that, The switching transistor (31) is a MOS transistor Q5, and a sixth resistor R6 is connected in parallel between the gate and source of the MOS transistor Q5.

8. The constant voltage dimming power supply output short-circuit protection circuit as described in claim 1, characterized in that, 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 transistor (31). The first input pin of the comparator N1A is connected to the reference voltage, and the second input pin is connected between the eighth resistor R8 and the switch transistor (31) after being connected in series with the thirteenth resistor R13.

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