Protection circuit and LED driving circuit

The present disclosure relates to a technology of switching power supply, and more particularly, to a protection circuit and an LED driving circuit.

FIG. 1 is a systematic block diagram showing an LED (light emitting diode) backlight module provided in an existing skill. As shown in FIG. 1 , the LED backlight module includes a rectifier filter module, a DC-DC converting module, a high-frequency rectifier filter module, a boost circuit 101 , an LED load, and an output feedback module. In the existing LED backlight module, an alternating current U_vin of 220V passes through the rectifier filter module, the DC-DC converting module, and the high-frequency rectifier filter module, and then is outputted as a first power source U 1 and a second power source U 2 . Generally, the second power source U 2 is used to drive a chip board/CB and the first power source U 1 is used to drive the LED load.

Usually, the existing boost circuit is required to cooperate with an LED driving chip to drive the LED load. FIG. 2 is a schematic diagram showing the existing boost circuit 101 and the LED load. As shown in FIG. 2 , the booster circuit 101 is used to pull up the first power source U 1 and then supply it to the LED load. The booster circuit 101 includes an LED driving chip M 1 and a switch Q 1 . The first power source U 1 also provides a driving voltage for the LED driving chip M 1 . However, the range of the driving voltage is too wide such that the LED driving chip M 1 works under a lower voltage. The LED driving chip M 1 starts to work when the first power source U 1 is low in voltage such that the current flowing through the switch Q 1 is too large, causing a damage of the switch Q 1 and reducing the reliability of the LED driving circuit.

Therefore, there is a need to provide a protection circuit and an LED driving circuit for solving the problems caused in the existing skills.

The objective of the present disclosure is to provide a protection circuit and an LED driving circuit for improving the reliability of an existing LED backlight module.

The present disclosure provides a protection circuit, which includes:

a Zener diode, a potential dividing unit, a first switch unit, and a second switch unit;

a cathode of the Zener diode is connected to the first power source and an anode of the Zener diode is connected to an input terminal of the potential dividing unit;

the first switch unit has a control terminal connected to an output terminal of the potential dividing unit, an input terminal connected to the second power source, and an output terminal connected to a control terminal of the second switch unit, and under control of a first control signal outputted by the output terminal of the potential dividing unit, the first switch unit is configured to output a second control signal to the control terminal of the second switch unit;

the second switch unit has an input terminal connected to the second power source and an output terminal connected to the boost circuit, the second switch unit is configured to output a voltage to the boost circuit under control of the second control signal;

the boost circuit includes an LED driving chip, the output terminal of the second switch unit is connected to a start terminal of the LED driving chip, the boost circuit has an input terminal connected to the first power source for pulling up a voltage outputted by the first power source;

the potential dividing unit including a first resistor and a second resistor;

the first resistor has a first terminal connected to the anode of the Zener diode, and a second terminal connected to a first terminal of the second resistor and the control terminal of the first switch unit, the second resistor has a grounded second terminal.

In the protection circuit of the present disclosure, the first switch unit includes a third resistor, a fourth resistor, a first capacitor, and a first switch;

the third resistor has a first terminal connected to the output terminal of the potential dividing unit, and a second terminal connected to a first terminal of the first capacitor and a control terminal of the first switch, the first capacitor has a grounded second terminal;

the fourth resistor has a first terminal connected to the second power source, and a second terminal connected to a first terminal of the first switch and the control terminal of the second switch unit, the first switch has a grounded second terminal.

In the protection circuit of the present disclosure, the second switch unit includes a fifth resistor and a second switch;

the fifth resistor has a first terminal connected to the second power source, and a second terminal connected to a first terminal of the second switch and the boost circuit;

the second switch has a control terminal connected to the control terminal of the second switch unit, and a grounded second terminal.

In the protection circuit of the present disclosure, the first switch and the second switch are NPN-type transistors, and the control terminals, the first terminals, and the second terminals of the first switch and the second switch are a base, a collector, and an emitter, respectively.

In the protection circuit of the present disclosure, the first switch unit includes a third resistor, a fourth resistor, a fifth resistor, a first capacitor, and a first switch;

the third resistor has a first terminal connected to the output terminal of the potential dividing unit, and a second terminal connected to a first terminal of the first capacitor and a control terminal of the first switch, the first capacitor has a grounded second terminal;

the fourth resistor has a first terminal connected to the second power source, and a second terminal connected to a first terminal of fifth resistor and the control terminal of the second switch unit, the fifth resistor has a second terminal connected to a first terminal of the first switch, the first switch has a grounded second terminal.

In the protection circuit of the present disclosure, the second switch unit includes a second switch;

the second switch has a first terminal connected to the second power source, a control terminal connected to the first terminal of the fifth resistor, and a second terminal connected to the boost circuit.

In the protection circuit of the present disclosure, the first switch is a NPN-type transistor and the second switch is a PNP-type transistor, and the control terminal, the first terminal, and the second terminal of the first switch are a base, a collector, and an emitter, respectively, and the control terminal, the first terminal, and the second terminal of the second switch are a base, an emitter, and a collector, respectively.

The present disclosure further provides a protection circuit, which includes:

a Zener diode, a potential dividing unit, a first switch unit, and a second switch unit;

a cathode of the Zener diode is connected to the first power source and an anode of the Zener diode is connected to an input terminal of the potential dividing unit;

the first switch unit has a control terminal connected to an output terminal of the potential dividing unit, an input terminal connected to the second power source, and an output terminal connected to a control terminal of the second switch unit, and under control of a first control signal outputted by the output terminal of the potential dividing unit, the first switch unit is configured to output a second control signal to the control terminal of the second switch unit;

the second switch unit has an input terminal connected to the second power source and an output terminal connected to the boost circuit, the second switch unit is configured to output a voltage to the boost circuit under control of the second control signal.

In the protection circuit of the present disclosure, the boost circuit includes an LED driving chip, the output terminal of the second switch unit is connected to a start terminal of the LED driving chip, the boost circuit has an input terminal connected to the first power source for pulling up a voltage outputted by the first power source.

In the protection circuit of the present disclosure, the potential dividing unit includes a first resistor and a second resistor;

the first resistor has a first terminal connected to the anode of the Zener diode, and a second terminal connected to a first terminal of the second resistor and the control terminal of the first switch unit, the second resistor has a grounded second terminal.

In the protection circuit of the present disclosure, the first switch unit includes a third resistor, a fourth resistor, a first capacitor, and a first switch;

the third resistor has a first terminal connected to the output terminal of the potential dividing unit, and a second terminal connected to a first terminal of the first capacitor and a control terminal of the first switch, the first capacitor has a grounded second terminal;

the fourth resistor has a first terminal connected to the second power source, and a second terminal connected to a first terminal of the first switch and the control terminal of the second switch unit, the first switch has a grounded second terminal.

In the protection circuit of the present disclosure, the second switch unit includes a fifth resistor and a second switch;

the fifth resistor has a first terminal connected to the second power source, and a second terminal connected to a first terminal of the second switch and the boost circuit;

the second switch has a control terminal connected to the control terminal of the second switch unit, and a grounded second terminal.

In the protection circuit of the present disclosure, the first switch and the second switch are NPN-type transistors, and the control terminals, the first terminals, and the second terminals of the first switch and the second switch are a base, a collector, and an emitter, respectively.

In the protection circuit of the present disclosure, the first switch unit includes a third resistor, a fourth resistor, a fifth resistor, a first capacitor, and a first switch;

the third resistor has a first terminal connected to the output terminal of the potential dividing unit, and a second terminal connected to a first terminal of the first capacitor and a control terminal of the first switch, the first capacitor has a grounded second terminal;

the fourth resistor has a first terminal connected to the second power source, and a second terminal connected to a first terminal of fifth resistor and the control terminal of the second switch unit, the fifth resistor has a second terminal connected to a first terminal of the first switch, the first switch has a grounded second terminal.

In the protection circuit of the present disclosure, the second switch unit includes a second switch;

the second switch has a first terminal connected to the second power source, a control terminal connected to the first terminal of the fifth resistor, and a second terminal connected to the boost circuit.

In the protection circuit of the present disclosure, the first switch is a NPN-type transistor and the second switch is a PNP-type transistor, and the control terminal, the first terminal, and the second terminal of the first switch are a base, a collector, and an emitter, respectively, and the control terminal, the first terminal, and the second terminal of the second switch are a base, an emitter, and a collector, respectively.

According to above objective, the present disclosure further provides an LED driving circuit, which includes a protection circuit and a boost circuit connected to the protection circuit, the protection circuit including:

a Zener diode, a potential dividing unit, a first switch unit, and a second switch unit;

a cathode of the Zener diode is connected to the first power source and an anode of the Zener diode is connected to an input terminal of the potential dividing unit;

the first switch unit has a control terminal connected to an output terminal of the potential dividing unit, an input terminal connected to the second power source, and an output terminal connected to a control terminal of the second switch unit, and under control of a first control signal outputted by the output terminal of the potential dividing unit, the first switch unit is configured to output a second control signal to the control terminal of the second switch unit;

the second switch unit has an input terminal connected to the second power source and an output terminal connected to the boost circuit, the second switch unit is configured to output a voltage to the boost circuit under control of the second control signal.

In the LED driving circuit of the present disclosure, the boost circuit includes an LED driving chip, the output terminal of the second switch unit is connected to a start terminal of the LED driving chip, the boost circuit has an input terminal connected to the first power source for pulling up a voltage outputted by the first power source.

In the LED driving circuit of the present disclosure, the potential dividing unit includes a first resistor and a second resistor;

the first resistor has a first terminal connected to the anode of the Zener diode, and a second terminal connected to a first terminal of the second resistor and the control terminal of the first switch unit, the second resistor has a grounded second terminal.

Distinguishable from the existing skills, in the protection circuit and the LED driving circuit of the present disclosure, the present disclosure deploys a protection circuit, instead of providing a start voltage to the boost circuit directly using the first power source. Under control of the first control signal, the first switch unit of the protection circuit outputs the second control signal to the second switch unit. In this way, under control of the second control signal, the second switch unit outputs a voltage to the boost circuit. In such a manner, a voltage is outputted to the boost circuit to drive the boost circuit only when the voltage provided by the first power source is at a certain value, thereby improving the reliability of the circuit.

The technical schemes and other beneficial effects will be more apparent with reference to the detailed descriptions of the embodiments of the present disclosure below in accompanying with the drawings.

FIG. 1 is a systematic block diagram showing an LED (light emitting diode) backlight module provided in an existing skill.

FIG. 2 is a schematic diagram showing an existing boost circuit 101 and an LED load.

FIG. 3 is a systematic block diagram showing an LED backlight module provided in the present disclosure.

FIG. 4 is a schematic diagram showing a boost circuit 201 and an LED load in accordance with the present disclosure.

FIG. 5 is a schematic diagram showing a protection circuit in accordance with a first preferred embodiment of the present disclosure.

FIG. 6 is a schematic diagram showing a protection circuit in accordance with a second preferred embodiment of the present disclosure.

For more clearly explaining the technical schemes adopted in the present disclosure and their effects, the preferred embodiments of the present disclosure are described in detail with referring to the appending drawings. Obviously, the described embodiments are merely a part of embodiments of the present disclosure and are not all of the embodiments. Based on the embodiments of the present disclosure, other embodiments obtained by those of ordinary skill in the art without making any inventive effort are within the scope the present disclosure seeks to be protected.

FIG. 3 is a systematic block diagram showing an LED (light emitting diode) backlight module provided in the present disclosure. As shown in FIG. 3 , the LED backlight module of the present disclosure includes a rectifier filter module, a DC-DC converting module, a high-frequency rectifier filter module, a boost circuit 201 , an LED load, a protection circuit 202 , and an output feedback module. In the LED backlight module of the present disclosure, an alternating current U_vin of 220V passes through the rectifier filter module, the DC-DC converting module, and the high-frequency rectifier filter module, and then is outputted as a first power source U 1 and a second power source U 2 . The second power source U 2 is used to drive a chip board/CB. The first power source U 1 and the second power source U 2 are controlled by the protection circuit 202 to output a voltage to the boost circuit 201 to drive the LED load.

Specifically, FIG. 4 is a schematic diagram showing a boost circuit 201 and an LED load in accordance with the present disclosure. As shown in FIG. 4 , the boost circuit of the present disclosure has an input terminal connected to the first power source U 1 . Further, the boost circuit of the present disclosure further includes an LED driving chip M 2 and a switch Q 2 . The LED driving chip M 2 has a start terminal connected to an output terminal VIN of a second switch unit. The switch Q 2 has a control terminal connected to a control adjusting terminal SW of the LED driving chip M 2 . The switch Q 2 has a first terminal receiving an output voltage of the first power source Q 1 and has a second terminal connected to a feedback terminal CS of the LED driving chip M 2 . The LED driving chip M 2 starts to work when receiving a driving voltage from the output terminal VIN of the second switch unit. The switch Q 2 is controlled and adjusted using the SW terminal of the LED driving chip M 2 . An inductor L 1 stores energy when the switch Q 2 is turned on. The inductor L 1 releases the stored energy when the switch Q 2 is turned off The LED load is driven by a voltage outputted from an OVP terminal of the LED driving chip M 2 .

FIG. 5 is a schematic diagram showing a protection circuit in accordance with a first preferred embodiment of the present disclosure. As shown in FIG. 5 , the protection circuit includes a Zener diode D 1 , a potential dividing unit 501 , a first switch unit 502 , and a second switch unit 503 . The cathode of the Zener diode D 1 is connected to the first power source U 1 . The anode of the Zener diode D 1 is connected to an input terminal of the potential dividing unit 501 .

The first switch unit 502 has a control terminal connected to an output terminal of the potential dividing unit 501 . The first switch unit 502 has an input terminal connected to the second power source U 2 . The first switch unit 502 has an output terminal connected to a control terminal of the second switch unit 503 . The first switch unit 502 is configured to output a second control signal to the control terminal of the second switch unit 503 under control of a first control signal outputted by the output terminal of the potential dividing unit 501 .

The second switch unit 503 has an input terminal connected to the second power source U 2 and an output terminal VIN connected to the boost circuit. The second switch unit 503 is configured to output a voltage to the boost circuit under control of the second control signal.

Specifically, the potential dividing unit 501 includes a first resistor R 1 and a second resistor R 2 . The first resistor R 1 has a first terminal connected to the anode of the Zener diode D 1 and a second terminal connected to a first terminal of the second resistor R 2 and the control terminal of the first switch unit 502 . A second terminal of the second resistor R 2 is grounded.

The first switch unit 502 includes a third resistor R 3 , a fourth resistor R 4 , a first capacitor C 1 , and a first switch Q 3 . The third resistor R 3 has a first terminal connected to the output terminal of the potential dividing unit 501 and a second terminal connected to a first terminal of the first capacitor C 1 and a control terminal of the first switch Q 3 . A second terminal of the first capacitor C 1 is grounded. The fourth resistor R 4 has a first terminal connected to the second power source U 2 and a second terminal connected to a first terminal of the first switch Q 3 and the control terminal of the second switch unit 503 . A second terminal of the first switch Q 3 is grounded.

The second switch unit 503 includes a fifth resistor and a second switch Q 4 . The fifth resistor R 5 has a first terminal connected to the second power source U 2 and a second terminal connected to a first terminal of the second switch Q 4 and the boost circuit. The second switch Q 4 has a control terminal connected to the control terminal of the second switch unit 503 , and a second terminal of the second switch Q 4 is grounded.

The first switch Q 3 and the second switch Q 4 are NPN-type transistors. The control terminals, the first terminals, and the second terminals of the first switch and the second switch are a base, a collector, and an emitter, respectively.

The protection circuit further includes a second capacitor C 2 , which has a first terminal connected to the output terminal VIN of the second switch unit 503 and a grounded second terminal.

The working principle of the protection circuit is described as follows. When the voltage outputted from the first power source U 1 is greater than a regulated voltage value of the Zener diode D 1 , the Zener diode D 1 is turned on and the voltage outputted from the first power source U 1 is inputted to the input terminal of the potential dividing unit 501 , and then the output terminal of the potential dividing unit 501 outputs the first control signal to the control terminal of the first switch unit 502 . In this way, the first switch Q 3 is turned on. The second power source U 2 is outputted to the ground terminal via the fourth resistor R 4 and the first switch Q 3 such that the control terminal of the second switch unit 503 receives the second control signal. In this way, the second switch Q 4 is turned off The second power source U 2 outputs a voltage to the output terminal VIN of the second switch unit 503 via the input terminal of the second switch unit 503 . Similarly, when the voltage outputted from the first power source U 1 is smaller than the regulated voltage value of the Zener diode D 1 , the Zener diode D 1 is turned off, the first switch Q 3 is turned off, the second switch Q 4 is turned on, and the second power source U 2 is outputted to the ground terminal via the input terminal of the second switch unit 503 . In this way, there is no voltage outputted to the output terminal VIN of the second switch unit 503 .

FIG. 6 is a schematic diagram showing a protection circuit in accordance with a second preferred embodiment of the present disclosure. As shown in FIG. 6 , the protection circuit includes a Zener diode D 1 , a potential dividing unit 601 , a first switch unit 602 , and a second switch unit 603 . The cathode of the Zener diode D 1 is connected to the first power source U 1 . The anode of the Zener diode D 1 is connected to an input terminal of the potential dividing unit 601 .

The first switch unit 602 has a control terminal connected to an output terminal of the potential dividing unit 601 . The first switch unit 602 has an input terminal connected to the second power source U 2 . The first switch unit 602 has an output terminal connected to a control terminal of the second switch unit 603 . The first switch unit 602 is configured to output a second control signal to the control terminal of the second switch unit 603 under control of a first control signal outputted by the output terminal of the potential dividing unit 601 .

The second switch unit 603 has an input terminal connected to the second power source U 2 and an output terminal VIN connected to the boost circuit. The second switch unit 603 is configured to output a voltage to the boost circuit to drive the boost circuit under control of the second control signal.

Specifically, the potential dividing unit 601 includes a first resistor R 1 and a second resistor R 2 . The first resistor R 1 has a first terminal connected to the anode of the Zener diode D 1 and a second terminal connected to a first terminal of the second resistor R 2 and the control terminal of the first switch unit 602 . A second terminal of the second resistor R 2 is grounded.

The first switch unit 602 includes a third resistor R 3 , a fourth resistor R 4 , a fifth resistor R 5 , a first capacitor C 1 , and a first switch Q 3 . The third resistor R 3 has a first terminal connected to the output terminal of the potential dividing unit 601 and a second terminal connected to a first terminal of the first capacitor C 1 and a control terminal of the first switch Q 3 . A second terminal of the first capacitor C 1 is grounded. The fourth resistor R 4 has a first terminal connected to the second power source U 2 and a second terminal connected to a first terminal of fifth resistor R 5 and the control terminal of the second switch unit 603 . The fifth resistor R 5 has a second terminal connected to a first terminal of the first switch Q 3 . A second terminal of the first switch Q 3 is grounded.

The second switch unit 603 includes a second switch Q 4 . The second switch Q 4 has a first terminal connected to the second power source U 2 , a control terminal connected to the first terminal of the fifth resistor R 5 , and a second terminal connected to the boost circuit.

The first switch Q 3 is a NPN-type transistor and the second switch Q 4 is a PNP-type transistor. The control terminal, the first terminal, and the second terminal of the first switch Q 3 are a base, a collector, and an emitter, respectively. The control terminal, the first terminal, and the second terminal of the second switch Q 4 are a base, an emitter, and a collector, respectively.

The protection circuit further includes a second capacitor C 2 , which has a first terminal connected to the output terminal VIN of the second switch unit 603 and a grounded second terminal.

The working principle of the protection circuit is described as follows. When the voltage outputted from the first power source U 1 is greater than a regulated voltage value of the Zener diode D 1 , the Zener diode D 1 is turned on and the voltage outputted from the first power source U 1 is inputted to the input terminal of the potential dividing unit 601 , and then the output terminal of the potential dividing unit 601 outputs the first control signal to the control terminal of the first switch unit 602 . In this way, the first switch Q 3 is turned on. The second power source U 2 is outputted to the ground terminal via the fourth resistor R 4 , the fifth resistor R 5 , and the first switch Q 3 such that the control terminal of the second switch unit 603 receives the second control signal. In this way, the second switch Q 4 is turned on. The second power source U 2 outputs a voltage to the output terminal VIN of the second switch unit 603 via the input terminal of the second switch unit 603 . Similarly, when the voltage outputted from the first power source U 1 is smaller than the regulated voltage value of the Zener diode DE the Zener diode D 1 is turned off, the first switch Q 3 is turned off, the second switch Q 4 is turned off. In this way, there is no voltage outputted to the output terminal VIN of the second switch unit 603 .

In the present disclosure, by use of the protection circuit and the control of the first switch and the second switch, a voltage is outputted to the LED driving chip only when the voltage provided by the first power source is at a certain value, thereby improving the reliability of the circuit.

The present disclosure further provides an LED driving circuit including the protection circuit described in above embodiments. The protection circuit has been described detailedly in above embodiments, and is not repeated herein.

In the LED driving circuit of the present disclosure, by use of the protection circuit and the control of the first switch and the second switch, a voltage is outputted to the LED driving circuit only when the voltage provided by the first power source is at a certain value, thereby improving the reliability of the circuit.

While the preferred embodiments of the present disclosure have been illustrated and described in detail, various modifications and alterations can be made by persons skilled in this art. The embodiment of the present disclosure is therefore described in an illustrative but not restrictive sense. It is intended that the present disclosure should not be limited to the particular forms as illustrated, and that all modifications and alterations which maintain the spirit and realm of the present disclosure are within the scope as defined in the appended claims.