Patent ID: 7759875

Claim:
A current providing circuit, comprising: a transformer, having a primary coil and a secondary coil, wherein a first end of the primary coil receives a power source; a signal generating unit, coupled to the first end of the primary coil so as to generate a pulse width modulation (PWM) signal according to a level of the power source, wherein the signal generating unit increases a frequency of the PWM signal with increasing of the level of the power source, and the signal generating unit decreases the frequency of the PWM signal with decreasing of the level of the power source; a switching unit, having a control end, a first signal end and a second signal end, wherein the first signal end is coupled to a second end of the primary coil, the second signal end is coupled to a ground end, and the switching unit determines whether the first signal end and the second signal end are conducted according to the PWM signal received by the control end; a first capacitor, coupled between the first signal end and the ground end; and an output node, coupled to the secondary coil for outputting an AC voltage.