CN100463580C - Backlight device driving circuit with protection module - Google Patents

Abstract

A driving circuit of a light emitting diode comprises a transformer, a driving module and a protection module. The transformer has a primary coil and a secondary coil. The first end of the primary side coil is coupled to a voltage source, the first end of the secondary side coil is coupled to the light emitting diode, and the second end of the secondary side coil is grounded. In addition, the second end of the primary side coil of the transformer is coupled to the driving module, and the driving module determines whether to transmit power to the transformer according to a pulse width modulation signal and an error signal. The protection module is coupled with the secondary side coil to generate an error signal to the driving module when the driving voltage output to the light emitting diode by the transformer is smaller than a first preset voltage or larger than a second preset voltage.

Description

Backlight device driving circuit with protection module

technical field

The present invention relates to a driving technology of a light-emitting diode, and in particular to a driving technology of a light-emitting diode used in a backlight device.

Background technique

Most conventional backlight devices use cold cathode fluorescent lamps as light sources. However, due to the improvement of the technical level of photoelectric components in recent years, light-emitting diodes have many advantages such as small size, low operating voltage, long life, and high color saturation. Therefore, using light emitting diodes as the light source of the backlight device has become another new option.

Due to the manufacturing process, even the light emitting diodes on the same wafer will have different electrical characteristics, so (parallel) light emitting diodes in actual use have a large difference in luminous brightness. In order to improve the yield rate of the manufacturing process and reduce the manufacturing cost, most of the light-emitting diodes used in the current light-emitting diode backlight devices use series-connected light-emitting diodes as the light source, so that the current flowing through each light-emitting diode is equal. , while having nearly the same luminance.

Please refer to FIG. 1 which shows a circuit diagram of a conventional LED backlight device. Please refer to FIG. 1 , in the conventional LED backlight device, there are a plurality of LEDs 101 connected in series as light sources, and these LEDs 101 are finally grounded through a resistor 103 .

Please continue to refer to FIG. 1, in order to reduce the influence of the luminance of the light-emitting diode 101 changing with time drift, a pulse width modulation (PWM) controller 105 is configured in the backlight device to generate pulse width modulation. The signal Vpwm is used to control the brightness of the LED 101 . In the conventional backlight device, the PWM controller 105 sends the PWM signal Vpwm to the gate terminal of the NMOS transistor 107 . Wherein, the drain terminal of the NMOS transistor 107 is coupled to the voltage source VDD through the inductor 109 , coupled to the series LED 101 through the Schottky diode 111 , and grounded through the capacitor 113 . In addition, the source terminal of the NMOS transistor 107 is grounded.

In addition, the PWM controller 105 is also coupled to the node where the LED 101 and the resistor 103 are coupled to each other to detect the current of the LED 101 . In this way, the PWM controller 105 can determine the duty cycle of the PWM signal Vpwm according to the detection result, so as to adjust the brightness of the LED 101 .

The boost circuit shown in FIG. 1 generates an output DC voltage Vout higher than the voltage source VDD to drive each LED 101 . However, as the size of flat-panel displays increases, the size of the backlight device also needs to increase accordingly, resulting in more and more light-emitting diodes 101 required, and the required driving voltage is also higher. The boost circuit shown in FIG. 1 The boost ratio that can be provided is not high, and such a high driving voltage cannot be provided. Therefore, the design of using the inductor 101 as the boosting element is bound to be limited by the size of the voltage source VDD, and cannot more flexibly meet the demand for the continuous increase in the number of LEDs 101 connected in series.

In addition, when the number of light-emitting diodes 101 in series continues to increase, their driving voltage will increase, so that there is a need for high-voltage protection. The current LED backlight device only clamps the driving voltage below a certain voltage value through the Schottky diode. However, when the driving voltage is higher, Schottky diodes with higher voltage resistance are required, which not only increases the cost of components, but also continues to output high voltage instead of stopping output, which may also cause damage to other components.

Contents of the invention

Therefore, the present invention provides a driving circuit for light emitting diodes, which can drive a large number of light emitting diodes in series, so it can be applied to display panels of many different sizes.

The driving circuit of the light emitting diode provided by the present invention also has a better protection module, which can protect the driving circuit of the present invention from outputting too high or too low driving voltage.

The drive circuit of the light emitting diode provided by the present invention includes a transformer, a drive module and a protection module. Wherein, the transformer has a primary side coil and a secondary side coil. In the present invention, the first end of the primary coil is coupled to a voltage source, the first end of the secondary coil is coupled to the LED, and the second end of the secondary coil is grounded. In addition, the second end of the primary coil of the transformer is coupled to the driving module, and the driving module determines whether to transmit power to the transformer according to a pulse width modulation signal and an error signal. The protection module is coupled to the secondary side coil, so that when the driving voltage output from the transformer to the light-emitting diode is less than a first preset voltage or greater than a second preset voltage, an error signal is generated to the driving module, so as to The output of electric power is stopped.

In an embodiment of the present invention, the above protection module includes a first comparator, a first counter and an initial counter. The first comparator is used for judging whether the driving voltage is lower than the first preset voltage, and outputs a first comparison result. The first counter receives the first comparison result, and generates a first counting signal when the driving voltage is lower than the first preset voltage and lasts for a first preset time. However, in the present invention, the first counter is in a disabled state when the driving circuit is activated and has not exceeded a power-on preset time. In addition, the initial counter is used to generate an initial counting signal to enable the first counter after the driving circuit is activated and the power-on preset time elapses. The first count value output by the first counter is sent to a latch, and is sent to an inverter through the latch and then output to the driving module.

In addition, the protection module further includes a second comparator and a second counter. The second comparator is used for judging whether the driving voltage is higher than the second preset voltage, and outputs a second comparison result. The second counter receives the second comparison result, and generates a second counting signal when the driving voltage is greater than the second preset voltage for a second preset time. The second count signal is sent to an OR gate, and the OR gate not only receives the second count signal, but also receives the first count signal. In addition, the output of this OR gate is sent to the latch.

In some other optional embodiments, the above-mentioned second comparator determines the magnitude of the driving voltage and the second preset voltage. The difference is that the second comparator has a high hysteresis, and when the driving voltage is greater than the second preset voltage—a hysteresis voltage, the second comparator will generate an output with a high state to an OR gate. And this OR gate will also receive the output of the aforementioned latch, and the output of this OR gate will be sent to the aforementioned inverter.

The backlight device provided by the present invention includes a light emitting diode light source module. In addition, the backlight device of the present invention uses the above driving circuit to drive the LED light source module to emit light.

Since the present invention uses a transformer to convert the voltage source into a driving voltage to drive the light source, the present invention can adjust the magnitude of the driving voltage according to the number of LEDs connected in series without limitation. Therefore, the present invention can be more flexible in use.

In order to make the above and other objects, features and advantages of the present invention more comprehensible, preferred embodiments will be described in detail below together with the accompanying drawings.

Description of drawings

FIG. 1 is a circuit diagram of a conventional LED backlight device.

FIG. 2A is a circuit diagram of a backlight device according to the first embodiment of the present invention.

FIG. 2B is a circuit diagram of a backlight device applying the protection circuit of the present invention.

FIG. 3 is a circuit diagram of a backlight device according to a second embodiment of the present invention.

FIG. 4 shows a circuit diagram of a backlight device according to a third embodiment of the present invention

FIG. 5 is a timing diagram of a dimming signal and a PWM signal according to a preferred embodiment of the present invention.

101, 212: LED

103, 272, 292, 294: resistance

105, 280, 380, 480: Pulse width modulation (PWM) controller

107, 224: NMOS transistors

109, 236: Inductance

111: Schottky diode

200A, 200B, 300, 400: backlight device

210, 310, 410: light source module

222, 422: AND gate

220, 320, 420: drive module

230, 330, 430: Transformer

232: primary side coil

234: Secondary side coil

240, 340, 440: protection module

246, 248, 342: Comparator

250, 252, 260: Counter

254: OR gate

256: Latches

258: Inverter

276: capacitance

290: Voltage detection module

VDD: voltage source

Detailed ways

Preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Wherein the accompanying drawings illustrate various preferred embodiments of the present invention. The invention can also be implemented in many different ways and is not limited to the embodiments described here. The purpose of providing the embodiments here is to let those skilled in the related art fully understand the scope of the present invention. Hereinafter, like reference numerals denote like elements.

FIG. 2A is a circuit diagram of a backlight device according to the first embodiment of the present invention. Please refer to FIG. 2A , the backlight device 200A provided by the present invention includes a light source module 210 and a driving circuit composed of a driving module 220 , a transformer 230 and a protection module 240 . In an embodiment of the present invention, the light source module 210 may be composed of a plurality of LEDs 212 connected in series. Using the transformer 220 can provide a higher step-up ratio, and can provide a higher DC driving voltage to drive more light-emitting diodes in series.

In detail, the cathode terminal of each LED 212 is coupled to the anode terminal of the next LED 212 , and the last LED 212 can be grounded through the resistor 272 . Those skilled in the art should know that the LEDs 212 in the backlight device 200A may include white LEDs, red LEDs, blue LEDs and green LEDs.

Please continue to refer to FIG. 2A , the transformer 230 has a primary coil 232 and a secondary coil 234 , and the ratio of the two is 1 to n. In this embodiment, the first end of the primary side coil 232 is coupled to the voltage source VDD, and the second end is coupled to the driving module 220 . In addition, the first terminal of the secondary side coil 234 can be coupled to the light source module 210 through a diode 274, for example, coupled to the anode terminal of the first light emitting diode 212, while the second terminal of the secondary side coil 234 is grounded. In a preferred situation, the diode 274 can be implemented with a Schottky diode.

In addition to being coupled to the light source module 210 , the first end of the secondary side coil 234 is also coupled to the protection module 240 and grounded through the capacitor 276 . The output of the protection module 240 is sent to the driving module 220 , so that the driving module 220 determines whether to stop outputting the power of the voltage source VDD to the transformer 230 according to the output of the protection module 240 .

The driving module 220 may include an AND gate 222 and an NMOS transistor 224 . Wherein, the AND gate 222 receives the pulse width modulation signal Vpwm and the output of the protection module 240 . In addition, the output of the AND gate is coupled to the gate terminal of the NMOS transistor 224 , the drain terminal of the NMOS transistor 224 is coupled to the second terminal of the primary coil 232 , and the source terminal thereof is grounded. In an embodiment of the present invention, the AND gate can also receive an enable control signal EA (also called an error reset signal). The start control signal EA is also output to the counter 252, the counter 260 and the latch 256 at the same time. When the backlight device 200A starts or restarts, it will output a signal of EA=0, so that the NMOS transistor 224, the counter 252, the counter 260 and the latch The counter 256 resets to zero again, and after the backlight device 200A is started or restarted, EA=1, so as to start the NMOS transistor 224, the counter 252, the counter 260 and the latch 256.

In this embodiment, the pulse width modulation signal Vpwm may be generated by a pulse width modulation (PWM) controller 280 . In addition, the PWM controller 280 detects the voltage at the node where the light source module 210 is coupled to the resistor 272 , that is, detects the current flowing through the light source module 210 . In this way, the pulse width modulator 280 can control the duty cycle of the pulse width modulation signal Vpwm according to the detection signal of the light source module 210 , so that the light source module 210 can have a stable brightness. Certainly, the pulse width modulation (PWM) controller 280 can also generate the pulse width modulation signal Vpwm according to the detection signal of the voltage of the light source module 210 (eg, coupled to the voltage detection module 290 ).

In the voltage detection module 290 , resistors 292 and 294 are included, wherein the first terminal of the resistor 292 is coupled to the cathode terminal of the diode 274 , and is coupled to the first terminal of the secondary coil 234 through the diode 274 . In addition, the second terminal of the resistor 292 is grounded through the resistor 294 and coupled to the negative input terminal of the comparator 246 and the positive input terminal of the comparator 248 . The driving module 220 , the protection module 240 , the pulse width modulation controller 280 and the voltage detection module 290 can be integrated into an integrated circuit chip. Alternatively, the voltage detection module 290 is independent from the integrated circuit chip, so that the designer of the backlight device can distribute the ratio of the resistors 292 and 294 more freely, and can better match various backlight devices.

In addition, the positive input terminal of the comparator 246 receives a preset voltage Vr1 , and the negative input terminal of the comparator 248 receives a preset voltage Vr2 . In this way, the comparator 246 can compare the driving voltage VOUT with the preset voltage Vr1 , and generate a comparison result R1 to the counter 250 . Likewise, the comparator 248 can compare the driving voltage VOUT with the preset voltage Vr2 and generate a comparison result R2 to the counter 252 . In this embodiment, the comparators 246 and 248 are respectively used to detect whether the driving voltage VOUT is too low or too high, so the preset voltage Vr1 is smaller than the preset voltage Vr2.

Next, the operation process of the backlight device 200A will be described.

When the backlight device 200A starts up initially, the error reset signal EA is in a high state (ie EA=1). In order to prevent the backlight device 200A of the present invention from being mistaken because the driving voltage VOUT is too low when it is just turned on. Therefore, in the protection module 240, a counter 260 is also arranged. When the backlight device 200A is just turned on, the counter 260 will output a low-level signal of T0=0 and start counting. At this time, the counter 250 receives the low-level signal of T0=0 and is in a disabled state, so T1= 0.

In addition, the counter 252 is activated upon receiving EA=1. At this time, since the driving voltage VOUT is lower than the preset voltage Vr2, the comparator 248 outputs R2=0, so the counter 252 outputs T2=0. Therefore, the OR gate 254 outputs a low-level signal after receiving T1=0 and T2=0, and the latch 256 receives the low-level signal of the OR gate 254 and outputs a low-level signal after receiving EA=1 and starting, And after being inverted by the inverter 258 , a high-level signal of E1=1 is output. Thereby, when the backlight device 200A is started initially, EA=1 and E1=1, the AND gate 222 will generate the pulse width modulation signal Vpwm according to the pulse width modulation controller 280 to control the switch of the NMOS transistor 224, and The transformer 230 can convert the voltage source VDD into a driving voltage VOUT to drive the light source module 210 .

When the timer 260 counts up to a first predetermined time, if the EA is still at the high level signal of "1", the timer 260 will output a high level signal of T0=1. Therefore, the timer 250 starts to operate after receiving the T0=1 signal. Preferably, the first predetermined time of the timer 260 is the length of the start-up time normally required by the backlight device 200A, and the light source module 210 enters normal operation after the first predetermined time. Therefore, when the timer 250 starts to operate, the voltage detection module 290 outputs a detection signal voltage that is greater than the predetermined voltage Vr1 but less than the predetermined voltage Vr2. Therefore, after entering the normal operation state, the output signals R1 and R2 of the comparators 246 and 248 are both low-level signals, and the output signals T1 and T2 of the timers 250 and 252 are also low-level signals. Therefore, under normal startup, the latch 256 keeps outputting a low level signal, so that the signal E1 maintains the low level of “0”.

However, when the start-up failure or other error conditions cause the drive voltage VOUT to be too low, for example, when a user accidentally touches the secondary side coil 234 of the transformer 230, the drive voltage VOUT will pass through the gap between the human body and the ground. The formed discharge path is discharged. At this time, the driving voltage VOUT will be lower than the preset voltage Vr1, and the comparator 246 will output a high-level output signal R1 to the counter 250, so that the counter 250 starts counting.

When the driving voltage VOUT is lower than the preset voltage Vr1 for a second preset time, the counter 250 generates a count signal T1 in a high state to the OR gate 254 . In this way, the OR gate 254 sends an output of a high level state to the latch 256 . The latch 256 outputs and locks the output signal in a high level state, and after being inverted by the inverter 258 , an error signal E1 in a low state is generated for the AND gate 222 . Thereby, the transistor 224 can be turned off (turn off), and the voltage source VDD stops supplying power to the transformer 230 . However, the present invention will be excluded from this low voltage event, and the user restarts the backlight device 200A to make the error reset signal EA=0 and reset the AND gate 222, the counter 252, the counter 260 and the latch 256 before continuing to provide The driving voltage VOUT is supplied to the light source module 210 .

On the other hand, however, when some error conditions cause the driving voltage VOUT to be too high, the comparator 248 of the protection module 240 detects that the driving voltage VOUT is too high. At this time, when the driving voltage VOUT is greater than the preset voltage Vr2, the comparator 248 will generate a high-level output to the counter 252, so that the counter 252 starts counting. When the driving voltage VOUT is greater than the preset voltage Vr2 for a third preset time, the counter 252 generates a high-level count signal T2 to the OR gate 254 , and sends it to the latch 256 through the OR gate 254 . Then, the latch 256 outputs and latches an output signal in a high level state, and after being inverted by the inverter 254 , an error signal E1 in a low level state is also generated for the AND gate 222 . Therefore, the transistor 224 is also turned off, and the transformer 230 cannot supply the driving voltage VOUT to the light source module. Similarly, the present invention excludes this high voltage event, and after the user activates the backlight device 200A to make the error reset signal EA=0 and resets the AND gate 222, the counter 252, the counter 260 and the latch 256, the supply can be resumed. The driving voltage VOUT is supplied to the light source module 210 .

It can be known from the above description that when the timer 260 elapses for the first predetermined time, the protection module 240 starts to perform the protection function. As long as the driving voltage VOUT is too low or too high, the protection module 240 controls and locks the driving circuit 220 to stop operation, so that the transformer 230 cannot supply the driving voltage VOUT to the light source module. Unless the user restarts the backlight device 200A, the backlight device 200A will remain in the state of stopping the output, and the backlight device 200A can be normally activated after the error event is eliminated.

Of course, the T0 signal of the counter 260 of the present invention can also be directly input to the latch 256 instead of the timer 250, so that the latch 256 starts to operate after the T0 signal changes from 0 to 1 during the startup process. Likewise, it can also prevent the backlight device 200A from being mistaken because the driving voltage VOUT is too low when the backlight device 200A is just turned on as mentioned above.

In other optional embodiments, the protection circuit of the present invention can also be used in conventional boosting circuits besides being used in backlight devices boosted by transformers. For example, in FIG. 2B , the transformer is changed to an inductor 236 . The protection circuit 240 detects the drive voltage VOUT through the voltage detection module 290. When the drive voltage VOUT is too high or too low, the counter 252 or 250 will start counting. If it continues, the output of the driving voltage VOUT will be terminated and locked. After terminating and locking the output of the driving voltage VOUT, the backlight device 200B must be restarted to make the EA signal a low-level signal of 0 to reset the protection circuit and the driving circuit, so that the backlight device 200B can be operated again.

In addition, the error reset signal EA in the present invention is a control signal that can stop the system operation without stopping the power supply of the backlight device. Using this error reset signal EA, except when the backlight device is locked due to an error state, it is used to reset the backlight device to enable it to start again, and the system including the backlight device can control the backlight device by using the error reset signal EA. Start operations at the right time. In this way, the system can arrange the starting timing of the backlight device and other devices in the system to reduce mutual interference or achieve a better starting sequence.

FIG. 3 is a circuit diagram of a backlight device according to a second embodiment of the present invention. Please refer to FIG. 3 , the backlight device 300 is generally similar to the backlight device 200A provided in the first embodiment, and has a light source module 310 , a pulse width modulation controller 380 , a drive module 320 , a transformer 330 and a protection module 340 . As for the coupling relationship and operating principles of these components, those skilled in the art can refer to the light source module 210, the pulse width modulation controller 280, the driving module 220, the transformer 230 and the protection module 240 in the first embodiment. narrative.

However, the difference is that in the protection module 340, the comparator 342 with high hysteresis is used to replace the comparator 248 in the first embodiment. In this embodiment, the comparator 342 also compares the detection signal of the driving voltage Vout with the preset voltage Vr2. However, when the detection signal is greater than the preset voltage Vr2 by a hysteresis voltage (of the comparator 342 ), the comparator 342 will generate an output R3 in a high state. Therefore, in this embodiment, the protection module 340 can decrease a counter.

When the driving voltage Vout is greater than one hysteresis voltage above the preset voltage Vr2 , the comparator 342 will generate a high-level output R3 to the OR gate 344 . Wherein, the other input end of the OR gate 344 is to receive the output of the latch 256 . In this way, when the comparator 342 generates an output R3 in a high state, it will be transmitted to the inverter 346 through the OR gate 344, and after being inverted by the inverter 346, an error signal E2 in a low state will be generated to the AND gate 222. In particular, since the output of the comparator 342 does not pass through the latch, as long as the voltage of the driving voltage Vout returns to a normal state and the comparator 342 outputs the output R3 in a low level state again, the backlight device 300 will automatically restart. activation without requiring the user to manually enable the error reset signal EA.

FIG. 4 is a circuit diagram of a backlight device according to a third embodiment of the present invention. Please refer to FIG. 4 , the backlight device 400 provided by this embodiment is substantially the same as the backlight device 200A provided by the first embodiment, and both have a light source module 410, a pulse width modulation controller 480, a drive module 420, a transformer 430 and protection module 440. For the coupling relationship and operation principle of these components, those skilled in the art can refer to the light source module 210, the pulse width modulation controller 280, the driving module 220, the transformer 230 and the protection module in the first embodiment. 240 narrative.

Different from the first embodiment, the driving module 420 additionally receives the dimming signal DIM, so that the backlight device 400 has a dimming function. In this embodiment, the driving module 420 includes an AND gate 422 in addition to the AND gate 222 and the NMOS transistor 224 . Wherein, the AND gate 422 is used to receive the error reset signal EA and the dimming signal DIM, and the frequency of the dimming signal DIM is lower than the frequency of the pulse width modulation signal Vpwm. By controlling the duty cycle of the dimming signal DIM, the switching time of the drive module 420 can be controlled to achieve the effect of dimming

FIG. 5 is a timing diagram of a dimming signal and a PWM signal according to a preferred embodiment of the present invention. Please refer to FIG. 4 and FIG. 5 together. In this embodiment, when the brightness of the light source module 410 needs to be reduced, it is only necessary to send a dimming signal DIM with a frequency relatively lower than that of the pulse width modulation signal Vpwm (as shown in FIG. 5 ). shown) to the input terminal of AND gate 422. Then, the AND gate 222 can perform "AND" operation on the pulse width modulation signal Vpwm and the dimming signal DIM. In this way, an output signal K1 can be generated to the gate terminal of the transistor 224 to reduce the brightness of the light source module 410 . In contrast, when it is necessary to increase the brightness of the light source module, it is necessary to generate a dimming signal DIM with a relatively large duty cycle to the input terminal of the AND gate 422 .

In summary, the present invention has at least the following advantages:

A large multiple of the driving voltage is used to drive the light source, so the driving circuit provided by the present invention can be applied to backlight devices of various sizes.

2. Also because the present invention uses a transformer to generate the driving voltage, the present invention can not only boost the voltage to generate the driving voltage, but also use the step-down method to generate the driving voltage, making the present invention more flexible in use.

3. Since the present invention has a protection module, it can protect the operation of the light source under too low voltage or too high voltage.

4. The present invention can also have a dimming mechanism, allowing users to adjust the brightness of the backlight device according to actual needs.

Although the present invention has been disclosed above with preferred embodiments, it is not intended to limit the present invention. Anyone skilled in the art can make some changes and modifications without departing from the spirit and scope of the present invention. Therefore, this The scope of protection of the invention shall be subject to the definition of the technical solution of the aforementioned patent application.

Claims (15)

1. the drive circuit of a light-emitting diode is characterized in that it comprises:

One transformer has one lateral coils and a second siding ring, and wherein first end of this first siding ring is coupled to a voltage source, and first end of this second siding ring is coupled to the light-emitting diode of a plurality of series connection, and the second end ground connection of this second siding ring;

One PWM controller produces a pulse-width modulation signal in order to the detection signal according to those light-emitting diodes;

One drives module, is coupled to second end of the first siding ring of this transformer, and transmits electric power to this transformer according to this pulse-width modulation signal; And

One protection module, couple this transformer, in order to the driving voltage that exports those light-emitting diodes when this transformer to during less than one first voltage or greater than one second voltage, then produce a rub-out signal and drive module to this, wherein this driving module stops to transmit electric power to this transformer according to this rub-out signal;

Wherein this driving module comprises: one with door, in order to receive this pulse-width modulation signal and this rub-out signal; And a nmos pass transistor, its gate terminal couples this and the output of door, and its drain electrode end couples second end of this first siding ring, and its source terminal ground connection.

2. the drive circuit of light-emitting diode according to claim 1, it is characterized in that wherein said driving module further receives a dim signal in order to adjust the brightness of those light-emitting diodes, wherein the frequency of this dim signal is different with the frequency of this pulse-width modulation signal.

3. the drive circuit of light-emitting diode according to claim 1 is characterized in that it further comprises a detecting voltage module, and producing a detecting voltage signal, and this protection module comprises according to this driving voltage:

One first comparator is in order to comparing this detecting voltage signal and one first predeterminated voltage, to judge that this driving voltage is whether less than first voltage and export one first comparative result;

One first counter receives this first comparative result, and produces one first count signal when this driving voltage continues one first Preset Time less than this first voltage; And

One fastens the lock device, receives this first count signal.

4. the drive circuit of light-emitting diode according to claim 3; it is characterized in that wherein said protection module further comprises an original counter; in order to be activated at this drive circuit and, just to produce an initial count signal, start this first counter through behind the start Preset Time.

5. the drive circuit of light-emitting diode according to claim 3 is characterized in that wherein said protection module further comprises:

One second comparator is in order to comparing this detecting voltage signal and one second predeterminated voltage, to judge that this driving voltage is whether greater than second voltage and export one second comparative result;

One second counter receives this second comparative result, and produces one second count signal when this driving voltage continues one second Preset Time greater than this second voltage; And

One or door, receive this first count signal and this second count signal, and output is delivered to this fasten the lock device.

6. the drive circuit of light-emitting diode according to claim 3 is characterized in that wherein said protection module further comprises:

One hysteresis, second comparator in order to this detecting voltage signal and one second predeterminated voltage are compared, and is exported one second count signal according to comparative result; And

One or door, receive this and fasten the lock output signal of device and this second count signal.

7. back lighting device is characterized in that it comprises:

One LED light source module;

One stepup transformer is coupled to a voltage source and this LED light source module, drives this LED light source module to produce a direct current driving voltage;

One protection module couples this stepup transformer, in order to when this driving voltage during greater than one first predetermined voltage, then produces a rub-out signal; And

One drives module, stops output power to this LED light source module according to this rub-out signal.

8. back lighting device according to claim 7 is characterized in that wherein said driving module comprises:

One with door, in order to receive pulse-width modulation signal and this rub-out signal produce according to the detection signal of this LED light source module; And

One nmos pass transistor, its gate terminal couple this and the output of door, and its drain electrode end couples this stepup transformer, and its source terminal ground connection.

9. back lighting device according to claim 8, it is characterized in that wherein said driving module further receives a dim signal in order to adjust the brightness of this LED light source module, wherein the frequency of this dim signal is different with the frequency of this pulse-width modulation signal.

10. back lighting device according to claim 7 is characterized in that wherein said protection module comprises to fasten the lock device, in this driving voltage greater than this first predetermined voltage and continue this Preset Time finger lock to continue to produce this rub-out signal.

11. back lighting device according to claim 7; it is characterized in that it further comprises a detecting voltage module; protect module to produce a detecting voltage signal to this according to this driving voltage, so that this protection module judges that whether this driving voltage is greater than this first predetermined voltage.

12. back lighting device according to claim 7 is characterized in that wherein said driving module couples a reset signal, to determine whether output power is to this LED light source module.

13. back lighting device according to claim 7, wherein this protection module more produces this rub-out signal during less than one second predetermined voltage in this driving voltage.

14. back lighting device according to claim 7, wherein this protection module more produces this rub-out signal in this driving voltage during less than one second predetermined voltage and after continuing a Preset Time.

15. back lighting device according to claim 7, wherein this protection module comprises and fastens the lock device, in this driving voltage less than this second predetermined voltage and continue this Preset Time finger lock to continue to produce this rub-out signal.

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