PWM Controller with Single Core Multivibrator

A new PWM controller with simple structure is presented. This controller consists of a modified transistor-core multivibrator having a single saturable core and is capable of changing the oscillation frequency with ease by a low control voltage. Accordingly, if this controller is applied to a small DC power supply or a feedback element of the switching regulator, a considerable reduction of the number of components is given in comparison with that of IC type. Furthermore, because the output signal has the nearly constant V/f ratio, the PWM controller is suitable for a simple speed control circuit of the small AC motor.