Light emitting diode driving circuit, backlight unit and liquid crystal display incorporating the same

An LED driving circuit, comprising:

• an LED driving voltage generator which generates a driving voltage to drive an LED;
• a pulse width modulation (PWM) control unit which outputs a PWM signal having a predetermined duty ratio;
• and
• a main switching unit which controls the driving voltage applied to the LEDs in accordance with the PWM signal,
• wherein the PWM control unit comprises:
• a controller including an error amplifier which detects an error between a reference voltage and a driving voltage and amplifies the detected error;
• an oscillator which outputs a pulse signal with a predetermined oscillation frequency;
• a comparator which compares the pulse signal output from the oscillator with an output voltage from the error amplifier to generate the PWM signal;
• and an overcurrent sensor which senses an overcurrent applied to the main switching unit and cuts off an output of the PWM signal whenever the overcurrent is sensed;
• a high frequency damper connected to the main switching unit to prevent malfunction of the controller due to noise;
• a current limiter which synchronizes a current applied to the main switching unit with the oscillation frequency of the pulse signal output from the oscillator;
• a noise remover connected to the error amplifier to reduce an external noise effect;
• an output controller which cuts off the output of the PWM signal output from the controller whenever the driving voltage is an overvoltage;
• and
• a controller heat radiation circuit which prevents current from being applied to the controller whenever the main switching unit is turned off.

A backlight unit, comprising:

• a plurality of LEDs;
• and
• an LED driving circuit for driving the plurality of LEDs,
• wherein the LED driving circuit comprises:
• an LED driving voltage generator which generates a driving voltage to drive the plurality of LEDs;
• a pulse width modulation (PWM) control unit which outputs a PWM signal having a predetermined duty ratio;
• and
• a main switching unit which controls the driving voltage applied to the plurality of LEDs in accordance with the PWM signal, and
• wherein the PWM control unit comprises:
• a controller including an error amplifier which detects an error between a reference voltage and a driving voltage and amplifies the detected error;
• an oscillator for outputting a pulse signal with a predetermined oscillation frequency;
• a comparator which compares the pulse signal output from the oscillator with an output voltage from the error amplifier to generate a PWM signal;
• and an overcurrent sensor which senses an overcurrent applied to the main switching unit and cuts off an output of the PWM signal whenever the overcurrent is sensed;
• a high frequency damper connected to the main switching unit to prevent malfunction of the controller due to noise;
• a current limiter which synchronizes a current applied to the main switching unit with the oscillation frequency of the pulse signal output from the oscillator;
• a noise remover connected to the error amplifier to reduce an external noise effect;
• an output controller which cuts the output of the PWM signal output from the controller when the driving voltage is an overvoltage;
• and
• a controller heat radiation circuit which prevents current from being applied to the controller when the main switching unit is turned off.

A liquid crystal display (LCD), comprising:

• a backlight unit including a plurality of LEDs and an LED driving voltage generator which generates a driving voltage to drive the plurality of LEDs;
• and
• an LCD panel positioned on top of the backlight unit and including a thin film transistor (TFT) substrate, a color filter substrate facing the TFT substrate and a liquid crystal layer disposed between the TFT substrate and the color filter substrate,
• wherein the LED driving circuit comprises:
• an LED driving voltage generator which generates an LED driving voltage;
• a pulse width modulation (PWM) control unit which outputs a PWM signal having a predetermined duty ratio;
• and
• a main switching unit which controls the driving voltage applied to the plurality of LEDs in accordance with the PWM signal, and
• wherein the PWM control unit comprises:
• a controller including an error amplifier which detects an error between a reference voltage and a driving voltage and amplifies the detected error;
• an oscillator which outputs a pulse signal with a predetermined oscillation frequency;
• a comparator which compares the pulse signal output from the oscillator with an output voltage from the error amplifier to generate the PWM signal;
• and an overcurrent sensor which senses an overcurrent applied to the main switching unit and cuts off an output of the PWM signal whenever the overcurrent is sensed;
• a high frequency damper connected to the main switching unit to prevent malfunction of the controller due to noise;
• a current limiter which synchronizes a current applied to the main switching unit with the oscillation frequency of the pulse signal output from the oscillator;
• a noise remover connected to the error amplifier to reduce an external noise effect;
• an output controller which cuts off the output of the PWM signal output from the controller whenever the driving voltage is an overvoltage;
• and
• a controller heat radiation circuit which prevents current from being applied to the controller whenever the main switching unit is turned off.