Backlight driving circuit and liquid crystal display device
View Patent ↗A backlight driving circuit and a liquid crystal display device are disclosed. The backlight driving circuit is utilized for driving at least one light emitting diode bar and includes a power supply module, a conversion module, a comparison module, and a control module. The power supply module provides a driving current for the light emitting diode bar. The conversion module generates a conversion voltage according to the driving current. The comparison module compares the conversion voltage with a reference voltage. The control module controls whether the power supply module provides the driving current for the light emitting diode bar according to whether the conversion voltage is greater than the reference voltage. The backlight driving circuit and the liquid crystal display device of the present invention can limit the driving current flowing through the light emitting diode bar.
1. A backlight driving circuit, utilized for driving at least one light emitting diode bar, the backlight driving circuit comprising:
a power supply nodule for providing a driving current for the light emitting diode bar;
a conversion module electrically coupled to the power supply module for generating a conversion voltage according to the driving current;
a comparison module electrically coupled to the conversion module for comparing the conversion voltage with a reference voltage; and
a control module electrically coupled to the power supply module, the comparison module, and the light emitting diode bar,
wherein when the conversion voltage is greater than the reference voltage, the control module controls the power supply module to stop providing the driving current for the light emitting diode bar,
when the conversion voltage is smaller than the reference voltage, the control module controls the power supply module to provide the driving current for the light emitting diode bar;
wherein the conversion module comprises:
a photo coupler comprising a light emitting element and a switch element, the light emitting element being electrically coupled between the power supply module and a positive polarity end of the light emitting diode bar for transmitting the driving current; and
a first resistor having a first end and a second end,
wherein the switch element is electrically coupled between a voltage source and the first end of the first resistor for outputting a switch current according to a light intensity of the light emitting element, and the conversion voltage is obtained by multiplying the switch current by a resistance value of the first resistor.
2. The backlight driving circuit of claim 1 , wherein the comparison module comprises:
an operational amplifier comprising a non-inverting input, an inverting input, and an output, the non-inverting input electrically coupled to the conversion voltage, and the inverting input electrically coupled to the reference voltage; and
a first N-type metal-oxide-semiconductor transistor, the output of the operational amplifier electrically coupled to a gate of the first N-type metal-oxide-semiconductor transistor, and a source of the first N-type metal-oxide-semiconductor transistor electrically coupled to a ground end,
wherein when the conversion voltage is greater than the reference voltage, the output of the operational amplifier is at a high level, the first N-type metal-oxide-semiconductor transistor is turned on, and a drain of the first the N-type metal-oxide-semiconductor transistor is changed to a low level,
when the conversion voltage is smaller than the reference voltage, the output of the operational amplifier is at a low level, the first N-type metal-oxide-semiconductor transistor is turned off, and the drain of the first N-type metal-oxide-semiconductor transistor is changed to a high level.
3. The backlight driving circuit of claim 2 , wherein the control module comprises:
a control unit having an enable pin and a plurality of control pins, the enable pin electrically coupled to the drain of the first N-type metal-oxide-semiconductor transistor; and
a second N-type metal-oxide-semiconductor transistor electrically coupled to the control unit,
wherein when the drain of the first N-type metal-oxide-semiconductor transistor is changed to the low level, the control unit controls the power supply module to stop providing the driving current for the light emitting diode bar via the second N-type metal-oxide-semiconductor transistor,
when the drain of the first N-type metal-oxide-semiconductor transistor is changed to the high level, the control unit controls the power supply module to provide the driving current for the light emitting diode bar via the second N-type metal-oxide-semiconductor transistor.
4. A backlight driving circuit, utilized for driving at least one light emitting diode bar, the backlight driving circuit comprising:
a power supply module for providing a driving current for the light emitting diode bar;
a conversion module electrically coupled to the power supply module for generating a conversion voltage according to the driving current;
a comparison module electrically coupled to the conversion module for comparing the conversion voltage with a reference voltage; and
a control module electrically coupled to the power supply module, the comparison module, and the light emitting diode bar for controlling whether the power supply module provides the driving current for the light emitting diode bar according to whether the conversion voltage is greater than the reference voltage;
wherein the conversion module comprises:
a photo coupler comprising a light emitting element and a switch element, the light emitting element being electrically coupled between the power supply module and a positive polarity end of the light emitting diode bar for transmitting the driving current; and
a first resistor having a first end and a second end,
wherein the switch element is electrically coupled between a voltage source and the first end of the first resistor for outputting a switch current according to a light intensity of the light emitting element, and the conversion voltage is obtained by multiplying the switch current by a resistance value of the first resistor.
5. The backlight driving circuit of claim 4 , wherein when the conversion voltage is greater than the reference voltage, the control module controls the power supply module to stop providing the driving current for the light emitting diode bar.
6. The backlight driving circuit of claim 4 , wherein when the conversion voltage is smaller than the reference voltage, the control module controls the power supply module to provide the driving current for the light emitting diode bar.
7. The backlight driving circuit of claim 4 , wherein the comparison module comprises:
an operational amplifier comprising a non-inverting input, an inverting input, and an output, the non-inverting input electrically coupled to the conversion voltage, and the inverting input electrically coupled to the reference voltage; and
a first N-type metal-oxide-semiconductor transistor, the output of the operational amplifier electrically coupled to a gate of the first N-type metal-oxide-semiconductor transistor, a source of the first N-type metal-oxide-semiconductor transistor electrically coupled to a ground end,
wherein when the conversion voltage is greater than the reference voltage, the output of the operational amplifier is at a high level, the first N-type metal-oxide-semiconductor transistor is turned on, and a drain of the first the N-type metal-oxide-semiconductor transistor is changed to a low level,
when the conversion voltage is smaller than the reference voltage, the output of the operational amplifier is at a low level, the first N-type metal-oxide-semiconductor transistor is turned off, and the drain of the first N-type metal-oxide-semiconductor transistor is changed to a high level.
8. The backlight driving circuit of claim 7 , wherein the control module comprises:
a control unit having an enable pin and a plurality of control pins, the enable pin electrically coupled to the drain of the first N-type metal-oxide-semiconductor transistor; and
a second N-type metal-oxide-semiconductor transistor electrically coupled to the control unit,
wherein when the drain of the first N-type metal-oxide-semiconductor transistor is changed to the low level, the control unit controls the power supply module to stop providing the driving current for the light emitting diode bar via the second N-type metal-oxide-semiconductor transistor,
when the drain of the first N-type metal-oxide-semiconductor transistor is changed to the high level, the control unit controls the power supply module to provide the driving current for the light emitting diode bar via the second N-type metal-oxide-semiconductor transistor.
9. A liquid crystal display device comprising the backlight driving circuit of claim 4 .