Single-ended forward converter type conversion circuit

The typical structure of a single-ended forward converter conversion circuit is shown in the figure. Its circuit form is almost the same as that of a single-ended flyback converter, but its working conditions are completely different. When the switching transistor VT1 is turned on, the rectifier diode VD2 on the secondary side of the transformer is turned on. At this time, the power grid transmits energy to the load, and the filter inductor L stores energy; when VT1 is turned off, the inductor continues to release energy to the load through the freewheeling diode VD3. In a single-ended forward converter, a clamping coil must be used to limit the voltage spikes on the collector-emitter of the transistor and reset the flux of the high-frequency transformer. The clamp coil usually has the same number of turns as the primary coil and is tightly coupled to it. Due to the effect of the clamping coil, the maximum back voltage of the switching transistor VTl is limited to 2 times the power supply voltage. At this time, in order to meet the core reset conditions, that is, the magnetic flux establishment and reset times should be equal, so the duty cycle of this circuit cannot exceed 50%.