Constant-frequency control of quasi-resonant converters

An additional independent control needed to eliminate the undesirable variable switching frequency of quasi-resonant converters can be obtained if the output rectifier is replaced by an active switch. The concept is applicable to all classes of quasi-resonant converters. It is demonstrated that in addition to operation at constant switching frequency, selected classes of constant-frequency quasi-resonant (CF-QR) topologies feature extended range of accessible conversion ratios and load currents. A practical example of a constant-frequency multi-resonant (CF-MR) buck converter operating at 2 MHz is described.