Isolated switch-mode power supply and control circuit and control method for isolated switch-mode power supply

摘要

The present invention discloses an isolated switch-mode power supply, a control circuit and a control method thereof. The main power transistor and the synchronous rectifier transistor are connected respectively to the primary-side winding and secondary-side winding of the isolated switch-mode power supply. The voltage of the control terminal of the main power transistor starts to increase, the main power transistor is turned on gradually, the current flowing through the main power transistor starts to increase until reaches the predetermined current-limiting value; the current of the main power transistor is maintained at the current-limiting value by controlling the voltage of the control terminal of the main power transistor; the secondary-side synchronous rectifier transistor is turned off, the current of the main power transistor decreases from the current-limiting value to the normal operation value, and the main power transistor is completely in an ON condition.