Patent ID: 8552695

Claim:
A DC-DC converter configured to be coupled to a transformer and configured to be switched between a quasi-resonant discontinuous conduction mode and a fixed off time continuous conduction mode, the DC-DC converter comprising: a power switching device; a driver stage for said power switching device; a mode control logic circuit configured to generate an ON-pulse; a rising edge triggered flip-flop coupled to said driver stage and configured to be set by said mode control logic circuit; a current mode comparator configured to reset said rising edge triggered flip-flop and to compare a signal representative of current flowing through said power switching device with a signal representative of an output voltage of the DC-DC converter; said mode control logic circuit comprising a timer configured to start when a gate driver control signal applied to said driver stage turns said power switching device off and configured to generate a pulse when an off time interval elapses, a zero current detector circuit configured to sense a voltage on the transformer and generate a pulse when the voltage drops below a trigger threshold, and a combinatory logic circuit configured to OR pulse signals generated by said timer and said zero current detector circuit and generate the ON-pulse based thereon; and said mode control logic circuit further comprising a set/reset flip flop configured to be set by the gate driver control signal to thereby produce a frequency limiter output signal, a reference threshold comparator timer configured to generate an output signal which resets said set/reset flip flop and comprising a current path switch, and a triggered capacitance charging ramp generator comprising a logic gate configured to OR the gate driver control signal and the output signal of said reference threshold comparator timer to thereby generate an output signal to turn on said current path switch.