Active clamp flyback converter with shutdown protection

An integrated circuit used for an active clamp flyback converter, comprising:

• an auxiliary switch;
• a main power switch, coupled between the auxiliary switch and a reference ground;
• a control circuit, configured to generate a main control signal and an auxiliary control signal in response to a feedback voltage indicative of an output voltage of the active clamp flyback converter, to respectively control the main power switch and the auxiliary switch;
• and
• a shutdown detection circuit, configured to detect a shutdown condition of the active clamp flyback converter, to generate a shutdown signal;
• wherein
• the control circuit is configured to control the main power switch to be turned on and the auxiliary switch to be turned off in response to the shutdown signal, until a current flowing through the main power switch reaches a main current limit;
• and then the control circuit is configured to control the auxiliary switch to be turned on and the main power switch to be turned off, until a current flowing through the auxiliary switch reaches a zero reference, to control the integrated circuit to enter a protection mode.

A control circuit used in an active clamp flyback converter, the active clamp flyback converter including a main power switch and an auxiliary switch integrated at a single integrated circuit, the control circuit comprising:

• a first comparator, configured to compare a main sense signal indicative of a current flowing through the main power switch with a main current limit, to generate an over current signal;
• a second comparator, configured to compare an auxiliary sense signal indicative of a current flowing through the auxiliary switch with a zero reference, to generate a zero detect signal;
• and
• a flip flop, configured to generate a main control signal and an auxiliary control signal in response to the over current signal and a shutdown signal indicative of a shutdown condition of the integrated circuit, wherein the flip flop is configured to:
• control the main power switch to be turned on and the auxiliary switch to be turned off in response to the shutdown signal;
• and
• control the main power switch to be turned off and the auxiliary switch to be turned on in response to the over current signal.