FPGA-Based Pulse-Frequency Modulator with Adaptive Zero-Crossing Detection for Quasi-Resonant Pulsed Converters

The problem of changing the resonant pulse width in a quasi-resonant pulsed converter under the different load conditions are considered. The necessity of agree the switch-off signal with a zero-current or a zero-voltage transition is established. Digital pulse-frequency modulator based of FPGA and the auxiliary circuit for resonant curve observation, which allows automatically detecting zero transition, forecast and retuning the pulse duration, is implemented using VHDL. Proposed circuit allow correcting pulse duration for exactly switch-off at zero-crossing, and also taking into account of propagation delays and resonant curve deviations. Results are verified by simulation.