| CPC H02M 3/33571 (2021.05) [H02M 1/0058 (2021.05); H02M 1/083 (2013.01); H02M 3/33592 (2013.01); H02M 1/0009 (2021.05)] | 12 Claims |
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1. A half-bridge flyback power converter, comprising:
a first transistor controlled by a first signal;
a second transistor controlled by a second signal;
a third transistor controlled by a third signal, wherein the first transistor, the second transistor and the third transistor are directly connected to a switching node and configured to form a half-bridge circuit for switching a resonant tank which is electrically connected to the switching node, wherein the first transistor and the third transistor are directly connected in parallel and independently controllable, wherein the resonant tank includes a resonant capacitor and a primary winding of a transformer of the half-bridge flyback power converter, wherein the resonant capacitor and the primary winding are electrically connected in series from the switching node; and
a switching control circuit, configured to operably generate the first signal according to an input voltage of the flyback power converter, and generate the third signal according to an output voltage of the flyback power converter, and generate the second signal according to a feedback signal related to the output voltage of the half-bridge flyback power converter;
during a discontinuous conduction mode (DCM) operation, the switching control circuit operating in a first switching cycle controls the first signal to turn on the first transistor for a first period, wherein after the first period, the switching control circuit controls the first signal, the second signal and the third signal to turn off the first transistor, the second transistor and the third transistor for a first off-time period, wherein after the first off-time period, the switching control circuit controls the second signal to turn on the second transistor for a second period, wherein after the second period, the switching control circuit controls the first signal, the second signal and the third signal to turn off the first transistor, the second transistor and the third transistor for a second off-time period, wherein after the second off-time period, the switching control circuit controls the third signal to turn on the third transistor for a third period, wherein after the third period, the switching control circuit controls the first signal, the second signal and the third signal to turn off the first transistor, the second transistor and the third transistor for a third off-time period;
wherein the first transistor and the third transistor are configured respectively as an auxiliary low-side transistor and a primary low-side transistor of the half-bridge flyback power converter, wherein the auxiliary low-side transistor and the primary low-side transistor are directly connected in parallel between the switching node and a ground potential and are independently controllable, and the second transistor is configured as a high-side transistor of the half-bridge flyback power converter;
wherein the half-bridge flyback power converter further comprising a timer for timing the third off-time period; and
wherein the third off-time period of the timer is increased in response to the decrease of output power of the half-bridge flyback power converter.
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