Free ac/dc digital-power reference design has universal input and PFC
By Paul Rako, Technical Editor -- EDN, April 14, 2009
Microchip Technology has announced an ac/dc reference design that it based on the new dsPIC33F GS series of digital-power DSCs (digital-signal controllers). The unit works with a universal input-voltage range and produces three output voltages. The ac input can range from 85 to 265V, and frequencies range from 45 to 65 Hz; continuous-power-output rating is 300W. A front-end PFC (power-factor-correction)-boost circuit converts universal ac-input voltages to a 420V-dc bus voltage. Input-power factor is greater than 0.98. An isolated buck converter uses the 420V PFC bus to create a 12V, 30A intermediate bus. The converter uses a ZVT (zero-voltage-transition) circuit to reduce losses, increase efficiency, and reduce stress on the power MOSFETs. The 12V bus then feeds a multiphase synchronous buck converter that can produce 69A at 3.3V. The 12V bus also feeds a single-phase buck converter that produces 23A at 5V.
The reference design has one four-layer board for digital signals and another for the other power stages. The design features soft-start capability and synchronous rectification. One dsPIC33F digital power IC handles the PFC and primary-side ZVT-bridge control, and a second chip provides the control for the converter stages. The design also features automatic fault handling and flexible start-up capabilities, such as sequencing output voltages on and off. Each of the four power stages features efficiencies of greater than 90%. The two DSCs communicate across the isolation boundary through UARTs (universal asynchronous receiver/transmitters). The design provides for remote power management.
You can download complete documentation, including software and Gerber files, free from Microchip’s Web site at www.microchip.com/SMPS.
