Smart FET driver emulates rectifier in secondary-side applications
By Paul Rako, Technical Editor -- EDN, February 22, 2010
International Rectifier’s new IR11672 synchronous-rectification IC drives a MOSFET in the secondary-side of an ac/dc flyback and resonant half-bridge switched-mode power supply, providing the function of a rectification diode. The device increases a power supply’s efficiency because a FET’s forward-voltage drop is smaller than that of a Schottky diode. You connect an input comparator across the power MOSFET, enabling it to sense the direction of the rectified current. The IC operates from an 11.3 to 20V power supply and its drain-sense pin can withstand 200V. Maximum switching frequency is 500 kHz, turn-off propagation delay is 50 nsec, and turn-on delay is 60 nsec. The device provides peak FET-gate turn-off drive current of 7A, and the unit has both an enable pin and a gate-output pin with a 10.7V clamp circuit.
In addition to conventional gate-drive circuitry, the IR11672 contains minimum-on-time circuitry that blanks the comparator’s input to prevent spurious ringing and oscillation from turning the part off. This feature guarantees proper operation in continuous-, discontinuous-, and critical- conduction modes. The IR11672 provides secondary-side synchronous rectification in switch-mode power supplies. It comes in an eight-pin SOIC package, operates in the −40 to +150°C temperature range and sells for 92 cents (10,000).
