Liquid crystal display device

1. A liquid crystal display device comprising:

a liquid crystal display panel;

a backlight which includes at least one light emitting diode;

a main voltage step-up circuit which steps up a power supply voltage, and applies the stepped up voltage to the at least one light emitting diode;

a main control circuit which controls and drives the main voltage step-up circuit; and

an auxiliary voltage step-up circuit,

wherein the main voltage step-up circuit includes

a coil of which one end is connected to a power supply;

a main switching element which is connected between the other end of the coil and a ground potential, and which ON/OFF thereof is controlled by the main control circuit;

a diode which is connected to the other end of the coil; and

a smoothing capacitor which is connected to the diode, the smoothing capacitor being a ceramic capacitor,

wherein the auxiliary voltage step-up circuit is connected to the other end of the coil and configured to charge the smoothing capacitor,

the auxiliary voltage step-up circuit is ON when the main step-up voltage circuit is OFF, and compensates a potential change in the smoothing capacitor is included, and

wherein the auxiliary voltage step-up circuit includes

an auxiliary switching element which is connected between the other end of the coil and a ground potential; and

an auxiliary control circuit which controls ON/ OFF of the auxiliary switching element.

2. The liquid crystal display device according to claim 1 ,

wherein the main control circuit controls ON/OFF of the main voltage step-up circuit based on a PWM signal which is input from the outside,

wherein the auxiliary switching element is a switching transistor, and

wherein the auxiliary control circuit is configured of an oscillator and an AND circuit which is connected to a control electrode of the switching transistor, and obtains a logical conjunction between an output of the oscillator and an inversion signal of the PWM signal.

3. The liquid crystal display device according to claim 1 ,

wherein, the main control circuit sets the main voltage step-up circuit to an ON state when a PWM signal which is input from the outside is a first voltage level, and sets the main voltage step-up circuit to an OFF state when the PWM signal is a second voltage level which is different from the first voltage level,

wherein the auxiliary control circuit includes

an oscillator;

a differential circuit to which an output of the oscillator is input;

a resistance element which is connected between an output end of the differential circuit and a ground potential; and

a third switching element which is connected between the output end of the differential circuit and a ground potential,

wherein the auxiliary switching element and the third switching element are switching transistors,

wherein the switching transistor which configures the auxiliary switching element has a control electrode connected to the output end of the differential circuit, and

wherein the switching transistor which configures the third switching element is ON when the PWM signal is the first voltage level, and is OFF when the PWM signal is the second voltage level.

4. The liquid crystal display device according to any one of claims 1 to 3 ,

wherein the auxiliary switching element is an MOS transistor.

5. The liquid crystal display device according to claim 3 ,

wherein the third switching element is an NPN bipolar transistor.