Random switching frequency in a synchronous-asynchronous digital voltage-mode control for dc-dc converters

This paper investigates the application of a random carrier-frequency pulse width modulation technique to the mixed synchronous/asynchronous digital voltage-mode controller for dc-dc converters presented in (Trzynadlowski, 1999). In the considered control architecture, the turn-on switching event is determined asynchronously by comparing the converter output voltage with a synchronously generated voltage ramp driven by the digital control using a low-resolution digital-to-analog converter (DAC). Switch turn-off is determined synchronously by the system clock. In this work, the system has been provided with a pulse width modulator which performs a limited pool random carrier-frequency modulation; this provision ensures low EMI emission and simple hardware implementation without affecting the quality of the output voltage regulation. Experimental results on a synchronous buck converter, where the digital control has been implemented in field programmable gate array (FPGA), confirm the effectiveness of the proposed solution