Active clamp power converter and method of reducing shoot-through current during soft start

An active clamp flyback (ACF) power converter comprising:

• a voltage input connection and a voltage output connection;
• a transformer defining a first inductor with first and second leads, and second inductor with first and second leads, the first lead of the first inductor coupled to the voltage input connection, the first lead of the second inductor coupled to the voltage output connection, and the second lead of the second inductor coupled to a secondary-side common;
• a clamp transistor defining a gate, a source, and a drain, the drain of the clamp transistor coupled the first lead of the first inductor by way of a clamp capacitor, and the source of the clamp transistor coupled to a switch node defined by the second lead of the first inductor;
• a main transistor defining a gate, a source, and a drain, the drain of the main transistor coupled the switch node, and the drain of the main transistor coupled to a primary-side common;
• a control circuit coupled to the gate of the clamp transistor, and coupled to the gate of the main transistor, the control circuit to perform soft start of the ACF power converter by being configured to:
• hold the gate of the clamp transistor de-asserted during a first time period;
• apply a first switching signal having a first frequency to the gate of the main transistor during the first time period;
• and then
• apply a second switching signal having a second frequency to the gate of the main transistor during a second time period, and apply a third switching signal having the second frequency to the gate of the clamp transistor during the second time period.