Designing a Forward Converter Using TOPSwitch®-GX

This circuit makes it easier to design a forward converter using TOPSwitch-GX by ensuring that the transformer resets each cycle.

Figure 1. Forward convert reset sensing scheme

A sensing circuit is used in conjunction with the forward converter bias winding to sense the voltage waveform during the OFF time. While this voltage is high, a signal is applied to the TOPSwitch-GX L pin, disconnecting it from the S pin, thereby inhibiting the internal MOSFET from initiating another ON cycle. When the voltage signal on the bias winding starts to collapse, indicating that the transformer has been reset, the L pin is connected to the S pin, and switching is enabled.