Patent ID: 7202640
Filing Date: 2007-04-10
Classification: H02M,Y02B,Y02P

Abstract:
1. A power factor improving circuit in which AC power supply voltage of an AC power supply is rectified by a rectification circuit to obtain rectified voltage, the rectified voltage is inputted to a series circuit comprising a step up reactor and a main switch, the main switch being turned ON/OFF to improve a power factor of the AC power supply, and DC output voltage being obtained by a rectification smoothing circuit, the power factor improving circuit comprising: a current detector detecting current conducting through the step up reactor or current conducting through the main switch; an error voltage generator amplifying a difference between the output voltage and a reference voltage to generate an error voltage; a variable gain amplifier amplifying voltage being proportional to current detected by the current detector by varying a gain in accordance with a value of the error voltage; and a pulse width controller generating a pulse signal whose pulse width is controlled in accordance with a value of output of the variable gain amplifier that has a negative correlation with a duty of the pulse signal, and applying the pulse signal to the main switch to control the output voltage with respect to predetermined voltage.