HIGH POWER FACTOR COMPENSATING CIRCUIT

摘要

PURPOSE: A high power factor compensating circuit is provided to reduce the distortion of an input current by generating an inverse saw tooth wave signal capable of controlling an offset voltage. CONSTITUTION: An output voltage detector(210) detects an output voltage of a step-up type converter(100) to detect an error according to a change of the output voltage. A current detector(220) detects an input current flowing on an inductor when a switching transistor is turned on. A multiplier(230) multiplies an output signal from the current detector(220) by an output signal from the output voltage detector(210) to generate a voltage for controlling an input current according to the change of the output voltage. An inverse saw tooth wave signal generator(240) includes an oscillator(242), a differential amplifier, a current source, a current mirror, a current controller, and a variable resistor. A comparator(250) compares an inverse saw tooth wave signal from the inverse saw tooth wave signal generator(240) with a comparison signal of the multiplier(230) to determine turn-off time of the switching transistor. A driver(260) turns on the switching transistor in response to a clock signal of the oscillator(242) and turns off the switching transistor in response to an output signal of the comparator(250).