The design delivers a regulated 400-V, 60-W output. The TL494 switching regulator governs the operating frequency and regulates output voltage. Rl and Cl determine switching frequency, which is approximately 0.SRCâ€”100 kHz for the values shown. The TL494 directly drives the FET's gates with a voltage-controlled, pulse-width-modulated signal. After full-wave rectification, the output waveform is filtered by a choke-input arrangement. The 1 Âµ, 75 ÂµÂ¥ filter accomplishes the job nicely at 100 kHz.
A feedback scheme using R4, R5 and R6 provides for output-voltage regulation adjustment, with loop compensation handled by C2. Diodes Dl and D2 provide isolation and steering for the 33-V zener transient clamp, D3. Output regulation is typically 1.25% from no-load to the full 60-W design rating. Regulation is essentially determined by the TL494. Output noise and ripple consists mainly of positive and negative 0.8-V spikes occurring when the output stage switches.