Digital interleaved PFC design lowers costs, increases efficiency

Sept. 9, 2009
Realize the benefits of fully digital PFC for green power-supply designs

The Digital Interleaved Power Factor Correction (PFC) Reference Design demonstrates how to realize the benefits of fully digital PFC for green power-supply designs. Specifically, this free reference design provides an easy method to evaluate the power efficiency and features of Microchip’s dsPIC33 “GS” series of Digital Signal Controllers (DSCs) for Switch Mode Power Supplies (SMPSs), in an interleaved PFC application.

The trend toward digital power conversion is enabling green power-supply designs, along with smarter and more efficient power systems. This trend helps to lower the carbon footprint of power systems and ease the burden on the world’s strained power grids. High-performance power supplies are used in a wide variety of applications, including telecommunications and industrial equipment, digital televisions, lighting, air conditioners and other home appliances. Digital interleaved PFC improves the power supply’s overall efficiency, along with the input power factor, voltage regulation and the Total Harmonic Distortion (THD) of the input current.

“This reference design enables our customers to quickly bring the benefits of digital interleaved PFC to their products, and create a more efficient and greener power distribution grid,” said Sumit Mitra, vice president of Microchip’s High Performance Microcontroller Division. “It uses the flexible dsPIC33F “GS” series of DSCs, which enables easy customization and configuration via simple modifications to the control software.”

Advantages of digital interleaved PFC methods over older PFC techniques:

• Lower cost for high-power applications
• Smaller PFC inductor and magnetic volume
• Higher power density
• Lower ripple
• Easy implementation of sophisticated control algorithms
• Flexible software modifications to meet specific customer needs
• Simpler integration with other applications

The Digital Interleaved PFC Reference Design works with a universal input voltage range and produces a single, high-voltage DC output of up to 350W. Its dual-phase interleaved PFC software implements three compensators for voltage, current and load balancing. It also has a feed-forward compensator, based on the average input voltage. This reference design has six main blocks:

1. Input EMI filter and rectifier
2. Dual-phase interleaved PFC circuit with feedback
3. Plug-in module connector, populated with a dsPIC33FJ16GS504 DSC
4. User-interface circuit with programming connector and push buttons
5. 12V and 3.3V power-supply circuit
6. Fault-detection circuit for hardware protection

Additional key features include:
• Operates at universal input voltage (85-265 Vac, 45-65 Hz)
• Operates up to 350W sustained output
• Output voltages up to 400 Vdc
• Power factor correction of 0.998 at full load and 120 VAC input
• Current Total Harmonic Distortion (ITHD) of 3% at full load and 120 VAC

All of the documentation, software and Gerber files needed to build this reference design can be obtained for free from Microchip’s Web site at: Additionally, demonstration units are available from the Company’s field sales force.

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