The UC3548 family of PWM control ICs uses voltage feedforward control to regulate the output voltage of isolated power supplies. The UC3548 resides on the primary side and has the necessary features to accurately control secondary side short circuit current with average current mode control techniques. The UC3548 can be used to control a wide variety of converter topologies. In addition to the basic functions required for pulse width modulation, the UC3548 implements a patented technique of sensing secondary current from the primary side in an isolated buck derived converter. A current waveform synthesizer monitors switch current and simulates the inductor current downslope so that the complete current waveform can be constructed on the primary side without actual secondary side measurement. This information on the primary side is used by an average current mode control circuit to accurately limit maximum output current. The UC3548 circuitry includes a precision reference, a wide bandwidth error amplifier for average current control, an oscillator to generate the system clock, latching PWM comparator and logic circuits, and a high current output 4/97