Patent ID: 8339390

Claim:
A power supply circuit of a display device, for boosting an input voltage and supplying a driving voltage higher than the input voltage to the display device, comprising: a coil that is charged with charges corresponding to the input voltage; a switching element for controlling charging of the coil with the charges and discharging of the charged charges; a capacitor for stabilizing an output voltage in a charging period of the coil; an oscillator for generating a clock signal as a reference of the output voltage; a comparator for comparing the clock signal with the output voltage; a pulse control circuit for generating a control signal of the switching element in accordance with an output signal of the comparator; and a frequency control circuit for inputting a vertical synchronizing signal and a horizontal synchronizing signal of the display device, and controlling a frequency of the clock signal generated by the oscillator based on the input vertical synchronizing signal and the input horizontal synchronizing signal, wherein: the frequency control circuit counts a number of outputs of the horizontal synchronizing signal following an output of the vertical synchronizing signal; the frequency control circuit controls the frequency of the clock signal to be different for a first state in which the number of outputs of the horizontal synchronizing signal is between a first number of outputs and a second number of outputs which are previously set, and for a second state in which the number of outputs of the horizontal synchronizing signal is not between the first number of outputs and the second number of outputs; and the frequency of the clock signal for the first state is higher than the frequency of the clock signal for the second state.