Pulse width modulation controller operational in both current and

Abstract

A pulse width modulation controller is shown which includes an error amplifier, a multiplying portion, an oscillator, a comparator, a flop-flop and a logic gate. The error amplifier receives an externally input feedback voltage and a first reference voltage in order to compare each voltage, and, in a current mode, the multiplying portion outputs a voltage which is proportional to the multiplication product of a voltage generated from a power switching unit and the difference between a second reference voltage and a voltage output from the error amplifier, and, in a voltage mode, outputs a voltage which is proportional to the multiplication product of a ground voltage and the difference between the second reference voltage and the voltage output from the error amplifier. The oscillator generates a clock signal and an inverse sawtooth signal. The comparator compares the inverse sawtooth signal with the output voltage of the multiplying portion. The flip-flop outputs a logic low signal when the clock signal and the output voltage of the comparator are a logic high and a logic low, respectively, and outputs a logic low signal when the clock signal and the output voltage of the comparator are a logic low and a logic high, respectively. Also, the logic gate controls the power switching unit by outputting a logic low signal when either the clock signal or the output of the flip-flop is a logic high, and by outputting a logic high signal when the clock signal and the output of the flip-flop are both logic low.