Microchip’s Digital Power AC/DC Reference Design unit works with a universal input voltage range and produces three output voltages. The continuous power output rating of the unit is 300 watts. The front-end power factor correction (PFC) boost circuit converts universal AC input voltages to a 420 VDC bus voltage.

A full-bridge transformer isolated buck converter, incorporating a phase-shift Zero Voltage Transition (ZVT) circuit, produces 12 VDC at 30 amps from the 420 VDC bus. The phase-shift ZVT converter also provides output-voltage isolation from the AC mains input. A multi-phase synchronous buck converter then produces 3.3 VDC at 69 amps from the 12 VDC bus, and a single-phase buck converter produces 5 VDC at 23 amps from the 12 VDC bus.

The AC/DC Reference Design includes many advanced features and high performance to support today’s increasing demands for efficiency and control, and to reduce operating costs and minimize system cost while maintaining high levels of reliability. Key design specifications include the following:

Universal Inputs (85V – 265V AC, 45 – 65 Hz);

Boost PFC (PF > 0.98);

Soft-start (programmable);

Full-bridge ZVT (soft-switching);

Synchronous rectification;

12-Volt intermediate bus;

Multi-phase Synchronous Buck converter 3.3V output;

Single-phase 5.0V output;

Automatic fault handling;

Remote power-management capabilities;

Flexible start-up capabilities;

Greater than 90% efficiency on each of the four power-conversion stages.

The reference design is powered by one of Microchip’s new dsPIC33F “GS” series of DSCs, which controls the PFC boost circuit and the primary-side ZVT full-bridge circuit. A second “GS” series dsPIC33F monitors the 12 VDC bus voltage and controls the four buck converters. The two dsPIC DSCs communicate across the isolation boundary via Universal Asynchronous Receiver Transmitters (UARTs).

“The flexible new dsPIC33F “GS” series of DSCs are featured and priced to help ignite significant digital power innovation,” said Rich Hoefle, marketing manager of Microchip’s High Performance Microcontroller Division. “We could have configured the topology of this reference design any number of ways, using the same two DSCs. More than anything else, this reference design is a springboard for customers to develop their own intellectual property to differentiate their digital power solutions in the marketplace.”