Simplified sensing and A/D conversion for digitally controlled flyback DC-DC converters with on-line efficiency optimization

This paper presents simplified sensing and analog-to-digital (A/D) conversion techniques, targeting low-cost, low-pin-count controller implementation for digitally controlled flyback DC-DC converters with on-line efficiency optimization. Precise output voltage regulation is accomplished by sensing an auxiliary winding voltage on the primary side at the end of the diode conduction interval, thus eliminating the need for secondary-side circuitry and isolation in the feedback path. Furthermore, simple single-comparator analog-to-digital (A/D) conversion techniques are adopted for input current and input voltage sensing, allowing implementation of on-line efficiency optimization over wide ranges of operating points. Experimental results are shown for a digitally controlled 65-W flyback prototype.