Short-circuit self-locking protection circuit of LED dimming circuit

Abstract

The utility model relates to a short-circuit self-locking protection circuit of an LED dimming circuit. The LED dimming circuit comprises an LED lamp, a switching tube, a switching tube driving circuit and a current detection circuit. The short-circuit self-locking protection circuit comprises a self-locking circuit, a one-way conduction element and a driving control circuit. The self-locking circuit comprises a voltage division circuit, a first switching circuit and a second switching circuit; the first end of the voltage division circuit and the input end of the first switching circuit are respectively connected with power supply voltage, the output end of the voltage division circuit is connected with the controlled end of the first switching circuit, the second end of the voltage division circuit is connected with the first conduction end of the second switching circuit, and the second conduction end of the second switching circuit is grounded; the first end of the one-way conduction element is connected with the output end of the current detection circuit, and the second end of the one-way conduction element is connected with the second conduction end of the first switching circuit, the controlled end of the second switching circuit and the input end of the driving control circuit; and the output end of the driving control circuit is connected with the switching tube driving circuit. The circuit is simple, the cost is low, and the short-circuit protection has a self-locking function.

Description

TECHNICAL FIELD

[0001] The utility model relates to the protection circuit technology of LED light adjusting circuit. BACKGROUND

[0002] LED has the advantages such as small size, high brightness, long life, is widely used in the automobile field and industrial market. When LED load short circuit, need to protect the drive circuit, to avoid causing the damage of drive circuit. The short circuit protection circuit of LED light adjusting circuit on the market mainly has two kinds: one is through integrated chip detection protection, cost is high and the optional factory is not many, another kind of protection is relied on the power supply detection of LED short circuit, and this protection can lead to system power off restart. SUMMARY

[0003] The utility model provides a short circuit self-locking protection circuit of LED light adjusting circuit, its circuit is simple, cost is low, and short circuit protection has the function of self-locking, prevents the system from appearing repeated short circuit and leads to circuit damage.

[0004] The utility model discloses a kind of short-circuit self-locking protection circuits of LED dimming circuit, LED dimming circuit includes LED lamp, switch tube, switch tube drive circuit and current detection circuit, switch tube and current detection circuit are respectively connected in series in the loop that power supply is the power supply of LED lamp, current detection circuit is used to detect the drive current flowing through LED lamp, output corresponding to the voltage of drive current;The input end of switch tube drive circuit is used to receive PWM signal, the output end of switch tube drive circuit is connected with the controlled end of switch tube, to control the opening and shutdown of switch tube;Short-circuit self-locking protection circuit includes self-locking circuit, unidirectional conducting element and drive control circuit;Self-locking circuit includes voltage divider, first switch circuit and second switch circuit;The first end of voltage divider and the input end of first switch circuit are connected with power supply voltage respectively, the output end of voltage divider is connected with the controlled end of first switch circuit, the second end of voltage divider is connected with the first conducting end of second switch circuit, the second conducting end of second switch circuit is grounded;The first end of unidirectional conducting element is connected with the output end of current detection circuit, the second end of unidirectional conducting element is respectively connected with the second conducting end of first switch circuit, the controlled end of second switch circuit and the input end of drive control circuit, unidirectional conducting element allows current to flow from first end to second end;The output end of drive control circuit is connected with the control end of switch tube drive circuit;Drive control circuit is used to output first control signal when the drive current flowing through LED lamp is less than predetermined overcurrent threshold, to make switch tube drive circuit control the opening and shutdown of switch tube according to the input PWM signal, second switch circuit is used to be turned off when the drive current flowing through LED lamp is less than predetermined overcurrent threshold, to make first switch circuit be turned off;Drive control circuit is used to output second control signal when the drive current flowing through LED lamp is greater than or equal to predetermined overcurrent threshold, to make switch tube drive circuit control switch tube be turned off;Second switch circuit is used to be turned on when the drive current flowing through LED lamp is greater than or equal to predetermined overcurrent threshold, to make first switch circuit be turned on, drive control circuit is locked in the state of output second control signal.

[0005] The utility model at least has following advantages and characteristics:

[0006] 1, the utility model embodiment can carry out short-circuit protection to LED dimming loop through simple hardware circuit, when LED load short-circuit occurs, short-circuit self-locking protection circuit controls switch tube drive circuit to be turned off power switch tube on LED lamp loop immediately, to protect drive circuit;

[0007] 2, the utility model embodiment adopts discrete device to build hardware, and the quantity of device is few, and cost is low, and has self-locking function to short-circuit state, guarantee product and will not because repeated short-circuit lead to circuit damage. BRIEF DESCRIPTION OF DRAWINGS

[0008] Figure 1A principle block diagram of the short-circuit self-locking protection circuit of the LED dimming circuit according to an embodiment of the present application is shown.

[0009] Figure 2 A circuit diagram of the short-circuit self-locking protection circuit of the LED dimming circuit according to an embodiment of the present application is shown. DETAILED DESCRIPTION

[0010] The present application will be described in detail below in conjunction with the drawings and specific embodiments.

[0011] Figure 1 A principle block diagram of the short-circuit self-locking protection circuit of the LED dimming circuit according to an embodiment of the present application is shown, Figure 2 A circuit diagram of the short-circuit self-locking protection circuit of the LED dimming circuit according to an embodiment of the present application is shown, please refer to Figure 1 and Figure 2 The LED dimming circuit according to the embodiment of the present application comprises an LED lamp 1, a switch tube Q3, a switch tube driving circuit 3 and a current detection circuit 4. The short-circuit self-locking protection circuit 5 according to the embodiment of the present application comprises a self-locking circuit 51, a unidirectional conducting element D1 and a driving control circuit 53.

[0012] The switch tube Q3 and the current detection circuit 4 are respectively connected in series in a loop in which the power supply Vbat supplies power to the LED lamp 1. The current detection circuit 4 is used for detecting a driving current flowing through the LED lamp 1 and outputting a voltage corresponding to the driving current; an input end of the switch tube driving circuit 3 is used for receiving a PWM signal, and an output end of the switch tube driving circuit 3 is connected with a controlled end of the switch tube Q3, so as to control the opening and closing of the switch tube Q3.

[0013] In the embodiment, an anode end of the LED lamp 1 is connected with the power supply Vbat, and a cathode end of the LED lamp 1 is connected with a first conducting end of the switch tube Q3. The current detection circuit 4 comprises a current detection resistor R11, which is connected in series between a second conducting end of the switch tube Q3 and the ground.

[0014] Further, the current detection circuit 4 further comprises a filter circuit, an input end of the filter circuit is connected with a common connection point of the second conducting end of the switch tube Q3 and the current detection resistor R11, and an output end of the filter circuit is connected with a first end of the unidirectional conducting element D1. The filter circuit can filter out interference signals of the current detection resistor R11. In the embodiment, the filter circuit is an RC filter circuit, which is composed of a resistor R10 and a capacitor C1.

[0015] The switch tube Q3 is an NMOS tube, and the switch tube driving circuit 3 is an NMOS tube driving circuit. The gate, the drain and the source of the NMOS tube respectively constitute the controlled end, the first conduction end and the second conduction end of the switch tube Q3. The NMOS tube driving circuit comprises an NPN transistor Q1, a PNP transistor Q2, a PNP transistor Q4, a resistor R1, a resistor R2, a resistor R3, a resistor R4 and a resistor R5. The common connection point of the first end of the resistor R1 and the first end of the resistor R2 constitutes the input end of the switch tube driving circuit 3, the common connection point of the second end of the resistor R1 and the base of the NPN transistor Q1 constitutes the control end of the switch tube driving circuit 3, and the second end of the resistor R2 and the emitter of the NPN transistor Q1 are both grounded. The resistor R2 is pulled down to the ground, which can ensure the reliable turn-off of the NPN transistor Q1. The collector of the NPN transistor Q1 is connected to the common connection point of the first end of the resistor R3 and the base of the PNP transistor Q2, the second end of the resistor R3 is connected to the common connection point of the emitter of the PNP transistor Q2 and the power supply voltage VCC, the collector of the PNP transistor Q2 is connected to the first end of the resistor R4 and the base of the PNP transistor Q4, the second end of the resistor R4 is connected to the common connection point of the emitter of the PNP transistor Q4 and the controlled end of the switch tube Q3, the collector of the PNP transistor Q4 is grounded, and the resistor R5 is connected in parallel between the base and the collector of the PNP transistor Q4.

[0016] The self-locking circuit 51 comprises a voltage dividing circuit 510, a first switch circuit 511 and a second switch circuit 512. The first end of the voltage dividing circuit 510 and the input end of the first switch circuit 511 are connected to the power supply voltage VCC, the output end of the voltage dividing circuit 510 is connected to the controlled end of the first switch circuit 511, the second end of the voltage dividing circuit 510 is connected to the first conduction end of the second switch circuit 512, and the second conduction end of the second switch circuit 512 is grounded. In this embodiment, the voltage dividing circuit 510 comprises a resistor R7 and a resistor R8, and the resistor R7 and the resistor R8 are connected in series. The first end of the resistor R7 constitutes the first end of the voltage dividing circuit 510, the first end of the resistor R8 constitutes the second end of the voltage dividing circuit 510, and the common connection point of the second end of the resistor R7 and the second end of the resistor R8 constitutes the output end of the voltage dividing circuit 510.

[0017] The first end of the unidirectional conduction element D1 is connected to the output end of the current detection circuit 4, the second end of the unidirectional conduction element D1 is connected to the second conduction end of the first switch circuit 511, the controlled end of the second switch circuit 512 and the input end of the driving control circuit 53 respectively, and the unidirectional conduction element D1 allows current to flow from the first end to the second end. In this embodiment, the unidirectional conduction element D1 is a diode, and the anode and the cathode of the diode respectively constitute the first end and the second end of the unidirectional conduction element D1.

[0018] The output end of the drive control circuit 53 is connected with the control end of the switch tube drive circuit 3.

[0019] In the embodiment, the drive control circuit 53 comprises an NPN triode Q5 and a resistor R6, the first end of the resistor R6 constitutes the input end of the drive control circuit 53, the second end of the resistor R6 is connected with the base of the NPN triode Q5, the collector of the NPN triode Q5 is connected with the control end of the switch tube drive circuit 3, and the emitter of the NPN triode Q5 is grounded; the NPN triode Q5 is turned off when the driving current flowing through the LED lamp 1 is less than the predetermined overcurrent threshold value, and is turned on when the driving current flowing through the LED lamp 1 is greater than or equal to the predetermined overcurrent threshold value.

[0020] In the embodiment, the first switch circuit 511 comprises a PNP triode Q6, and the controlled end, the first conduction end and the second conduction end of the first switch circuit 511 are the base, the emitter and the collector of the PNP triode Q6 respectively. The second switch circuit 512 comprises an NPN triode Q7, and the controlled end, the first conduction end and the second conduction end of the second switch circuit 512 are the base, the collector and the emitter of the NPN triode Q7 respectively. The self-locking circuit comprises a resistor R9, the first end of the resistor R9 is connected with the controlled end of the drive control circuit 53 and the second conduction end of the first switch circuit 511 respectively, and the second end of the resistor R9 is connected with the second end of the unidirectional conduction element D1 and the controlled end of the second switch circuit 512 respectively.

[0021] The working principle of the short-circuit self-locking protection circuit of the LED dimming circuit according to an embodiment of the utility model is described as follows.

[0022] When the LED dimming circuit is working normally, the switch tube drive circuit 3 controls the opening and closing of the switch tube Q3 according to the input PWM square wave. When the level of the PWM signal is high, the NPN transistor Q1 is saturated and turned on, the collector of the NPN transistor Q1 is pulled to 0V, the base of the PNP transistor Q2 is also 0V, the PNP transistor Q2 meets the saturated conduction condition, and the collector voltage of the PNP transistor Q2 is basically the same as the supply voltage VCC. Since Q4 is a PNP transistor, the base and emitter voltages of the PNP transistor Q4 are equal, which cannot meet the conduction condition of the PNP transistor Q4, and the PNP transistor Q4 is in the off state. The supply voltage VCC is divided by the PNP transistor Q2 and the resistor R4, and can drive the switch tube Q3 to turn on. When the PWM signal is low, the NPN transistor Q1 cannot meet the conduction condition and is turned off, and the emitter and base voltages of the PNP transistor Q2 are the same, so the PNP transistor Q2 is also turned off. The base of the PNP transistor Q4 is pulled down to ground through the resistor R5, the PNP transistor Q2 is in the off state, and the PNP transistor Q4 is in the saturated conduction state, which can quickly discharge the gate voltage of the switch tube Q3 to 0V. In this way, the brightness of the LED lamp 1 can be adjusted according to the different duty cycles of the PWM.

[0023] When the LED dimming circuit is working normally, the current flowing through the current detection resistor R11 (which is equal to the driving current flowing through the LED lamp 1) is very small, less than the predetermined overcurrent threshold, and the voltage drop of the current detection resistor R11 is also small, which cannot reach the bias voltage to turn on the NPN transistors Q5 and Q7, so the NPN transistors Q5 and Q7 are in the off (off) state. Because the NPN transistor Q7 is turned off, the base of the PNP transistor Q6 is pulled up to the supply voltage VCC through the resistor R7, and the base voltage of the PNP transistor Q6 is basically the same as the collector voltage of the PNP transistor Q6, so the supply voltage VCC does not affect the collector voltage of the PNP transistor Q6, and does not cause the NPN transistor Q5 to be turned on, and does not affect the switch tube drive circuit 3. That is, when the LED dimming circuit is working normally, the short circuit protection self-locking circuit does not affect the normal working of the LED dimming circuit.

[0024] When the LED lamp 1 short circuit occurs in the driving circuit, the current value flowing through the current detection resistor R11 is very large, greater than or equal to a predetermined overcurrent threshold value, and the voltage drop value of the current detection resistor R11 is also very large, exceeding the forward voltage drop of the unidirectional conduction element D1 (diode) plus the turn-on bias voltage value of the NPN triode Q5 and the NPN triode Q7, so that the NPN triode Q5 and the NPN triode Q7 are turned on. After being turned on, the collector of the NPN triode Q5 and the NPN triode Q7 is pulled down to 0V, and the turn-on of the NPN triode Q5 can make the base of the NPN triode Q1 drive to quickly turn off, and as described above, the switch tube Q3 will also be quickly turned off. After the NPN triode Q7 is turned on, the supply voltage VCC is divided by resistors R7 and R8, and the base voltage of the PNP triode Q6 is lower than the emitter voltage, which meets the turn-on condition of the PNP triode Q6. After the PNP triode Q6 is turned on, VCC, resistor R9 and PNP triode Q6 form a positive feedback loop, and the NPN triode Q7 can be in a conductive state at all times. Due to the conductive state of the PNP triode Q6, the collector voltage of the PNP triode Q6 is close to the supply voltage VCC, and after the collector voltage of the PNP triode Q6 passes through resistor R6 and NPN triode Q5, the NPN triode Q5 will be always turned on due to the self-locking loop formed by the supply voltage VCC, resistors R7, R8, R9, PNP triode Q6 and NPN triode Q7 meeting the bias turn-on condition, and the collector of the NPN triode Q5 will be pulled down to 0V, and the NPN triode Q1 will be always turned off. In addition, due to the biasing effect of the unidirectional conduction element D1, the voltage of the short circuit self-locking loop does not affect the function of the current detection circuit composed of resistor R10, resistor R11 and capacitor C1, and the reliability of the self-locking loop is ensured.

[0025] The utility model discloses a short circuit protection circuit for LED light circuit, which can protect the driving circuit when the LED light circuit is short circuited.

[0026] Obviously, those skilled in the art can make various modifications and variations to the utility model without departing from the spirit and scope of the utility model. Thus, if these modifications and variations of the utility model fall within the scope of the utility model claims and their equivalents, the utility model also intends to include these modifications and variations.

Claims

1. A short-circuit self-locking protection circuit of an LED dimming circuit, the LED dimming circuit comprising an LED lamp, a switching tube, a switching tube driving circuit and a current detection circuit, the switching tube and the current detection circuit being connected in series in a loop in which a power supply supplies power to the LED lamp, the current detection circuit being configured to detect a driving current flowing through the LED lamp and output a voltage corresponding to the driving current; an input end of the switching tube driving circuit being configured to receive a PWM signal, and an output end of the switching tube driving circuit being connected to a controlled end of the switching tube to control opening and closing of the switching tube; characterized in that, The short-circuit self-locking protection circuit comprises a self-locking circuit, a unidirectional conducting element and a driving control circuit. The self-locking circuit comprises a voltage dividing circuit, a first switching circuit and a second switching circuit; a first end of the voltage dividing circuit and an input end of the first switching circuit are connected with a power supply voltage respectively; an output end of the voltage dividing circuit is connected with a controlled end of the first switching circuit; a second end of the voltage dividing circuit is connected with a first conducting end of the second switching circuit; and a second conducting end of the second switching circuit is grounded. A first end of the unidirectional conducting element is connected with an output end of the current detecting circuit; a second end of the unidirectional conducting element is connected with a second conducting end of the first switching circuit, a controlled end of the second switching circuit and an input end of the driving control circuit respectively; the unidirectional conducting element allows current to flow from the first end to the second end; and an output end of the driving control circuit is connected with a control end of the switch tube driving circuit. The driving control circuit is configured to output a first control signal when a driving current flowing through the LED lamp is less than a predetermined overcurrent threshold, so that the switch tube driving circuit controls opening and closing of the switch tube according to an input PWM signal; and the second switching circuit is configured to be turned off when the driving current flowing through the LED lamp is less than the predetermined overcurrent threshold, so that the first switching circuit is turned off. The driving control circuit is configured to output a second control signal when the driving current flowing through the LED lamp is greater than or equal to the predetermined overcurrent threshold, so that the switch tube driving circuit controls the switch tube to be turned off. The second switching circuit is configured to be turned on when the driving current flowing through the LED lamp is greater than or equal to the predetermined overcurrent threshold, so that the first switching circuit is turned on and the driving control circuit is locked in a state of outputting the second control signal.

2. The short-circuit self-locking protection circuit of the LED dimming circuit according to claim 1, characterized in that, The switch tube is an NMOS tube, and the switch tube driving circuit is an NMOS tube driving circuit.

3. The short circuit self-locking protection circuit of LED dimming circuit according to claim 2, characterized in that, The NMOS tube driving circuit comprises an NPN transistor Q1, a PNP transistor Q2, a PNP transistor Q4, a resistor R1, a resistor R2, a resistor R3, a resistor R4 and a resistor R5. A common connection point of a first end of the resistor R1 and a first end of the resistor R2 constitutes an input end of the switch tube driving circuit; a second end of the resistor R1 and a common connection point of a base of the NPN transistor Q1 constitute a control end of the switch tube driving circuit; a second end of the resistor R2 and an emitter of the NPN transistor Q1 are grounded; a collector of the NPN transistor Q1 is connected with a common connection point of a first end of the resistor R3 and a base of the PNP transistor Q2; a second end of the resistor R3 is connected with a common connection point of an emitter of the PNP transistor Q2 and the power supply voltage; a collector of the PNP transistor Q2 is connected with a first end of the resistor R4 and a base of the PNP transistor Q4 respectively; a second end of the resistor R4 is connected with a common connection point of an emitter of the PNP transistor Q4 and the controlled end of the switch tube; a collector of the PNP transistor Q4 is grounded; and the resistor R5 is connected in parallel between the base and the collector of the PNP transistor Q4.

4. The short-circuit self-locking protection circuit of the LED dimming circuit according to claim 1 or 3, characterized in that, The drive control circuit comprises an NPN transistor Q5 and a resistor R6, a first end of the resistor R6 constitutes an input end of the drive control circuit, a second end of the resistor R6 is connected with a base of the NPN transistor Q5, a collector of the NPN transistor Q5 is connected with a control end of the switch tube drive circuit, an emitter of the NPN transistor Q5 is grounded; the NPN transistor Q5 is turned off when a drive current flowing through the LED lamp is less than a predetermined overcurrent threshold, and is turned on when the drive current flowing through the LED lamp is greater than or equal to the predetermined overcurrent threshold.

5. The short self-locking protection circuit of LED dimming circuit according to claim 1, characterized in that, The voltage dividing circuit comprises a resistor R7 and a resistor R8, the resistor R7 is connected with the resistor R8 in series; a first end of the resistor R7 constitutes a first end of the voltage dividing circuit, a first end of the resistor R8 constitutes a second end of the voltage dividing circuit, a common connection point of a second end of the resistor R7 and a second end of the resistor R8 constitutes an output end of the voltage dividing circuit.

6. The short self-locking protection circuit of LED dimming circuit according to claim 1, characterized in that, The first switch circuit comprises a PNP transistor Q6, a controlled end, a first conduction end and a second conduction end of the first switch circuit are a base, an emitter and a collector of the PNP transistor Q6 respectively; The self-locking circuit comprises a resistor R9, a first end of the resistor R9 is connected with the controlled end of the drive control circuit and the second conduction end of the first switch circuit respectively, a second end of the resistor R9 is connected with the second end of the unidirectional conduction element and the controlled end of the second switch circuit respectively.

7. The short-circuit self-locking protection circuit of LED dimming circuit according to claim 1 or 6, characterized in that, The second switch circuit comprises an NPN transistor Q7, a controlled end, a first conduction end and a second conduction end of the second switch circuit are a base, a collector and an emitter of the NPN transistor Q7 respectively.

8. The short self-locking protection circuit of LED dimming circuit according to claim 1, characterized in that, The unidirectional conduction element is a diode D1, an anode and a cathode of the diode D1 constitute the first end and the second end of the unidirectional conduction element respectively.

9. The short self-locking protection circuit of LED dimming circuit according to claim 1, characterized in that, The anode end of the LED lamp is connected with the power supply, the cathode end of the LED lamp is connected with the first conduction end of the switch tube; The current detection circuit comprises a current detection resistor R11, the current detection resistor R11 is connected in series between the second conduction end of the switch tube and the ground.

10. The short circuit self-locking protection circuit of the LED dimming circuit according to claim 9, characterized in that, The current detection circuit further comprises a filter circuit, an input end of the filter circuit is connected with a common connection point of the second conduction end of the switch tube and the current detection resistor R11, an output end of the filter circuit is connected with the first end of the unidirectional conduction element.

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