The UC3848 family of PWM control ICs makes primary side average current mode control practical for isolated switching converters. Average current mode control insures that both cycle by cycle peak switch current and maximum average inductor current are well defined and will not run away in a short circuit situation. The UC3848 can be used to control a wide variety of converter topologies. In addition to the basic functions required for pulse width modulation, the UC3848 implements a patented technique of sensing secondary current in an isolated buck derived converter from the primary side. A current waveform synthesizer monitors switch current and simulates the inductor current down slope so that the complete current waveform can be constructed on the primary side without actual secondary side measurement. This information on the primary side allows for full DC control of output current.