High Power Two-Phase Digital

Power Factor Correction

Reference Design

IXRD100401-0916

Overview

This reference design builds upon IXYS Corporation’s Digital Power Control technology and extends it

to high power levels in the area of Power Factor Correction (PFC). It introduces fast switching, high

current, high voltage X2-class MOSFETs and incorporates Digital Inrush Current Control concepts

(IXYS reference designs IXRD1001 and IXRD1002). Functional control is based upon Zilog’s 8-bit

Z8F6481 microcontroller, a member of the Z8 Encore! XP F6482 Series of MCUs.

High power (1 kW and above) AC to DC converters with active PFC are designed to solve specific issues

arising at high power, including the following:

 Decrease high current ripples at PFC switching frequency in the input power line

 Maintain fast low-loss transfer of high inductor’s current from the switching device to the

load

 Provide efficient conversion in a wide load range

 Decrease high frequency electromagnetic interference (EMI) caused by PFC switching

devices operating at high current and voltage

 Decrease EMI caused by oscillations in the inductor during discontinuous mode at low

load that are a result of transforming energy stored in stray capacitance/inductance

 Design a low loss high frequency inductor to store and efficiently pump energy into the

output bulk capacitor

 Develop a robust current-balancing technology for polyphase PFC topology to reduce

current ripples in the input power line

 Create overload and overvoltage protections to ensure reliable performance in unexpected

situations for the end-user

In this reference design, input AC power line current ripples are reduced by using two-phase interleaved

conversion with pulse density modulation at low power. After the power drops below 50% of maximum

rated power, the second phase is disabled to reduce switching losses, while the microcontroller adjusts

appropriate parameters to continue an uninterrupted conversion.

The quasi-resonant mode is used to reduce EMI during high power conversion, while the device operates

in discontinuous mode with an active snubber at lower power. The selected conversion frequency is in the

100 kHz range, which allows for a decrease in component size yet provides high enough wattage for

power range devices.

The inductor current switching time is reduced to 10–15 ns depending on current value, which is in the

range of 12–18 A at 140 V–105 V AC input power line voltage respectively. Fast switching is achieved

by using fast X2-class MOSFETs and appropriate decoupling and layout (For more information, refer to

the device documentation). The inductor is built with high frequency E-core and Litz wire coil to obtain

high efficiency at high switching frequency.

The two-phase interleaving architecture used in this reference design requires thorough current balancing

to avoid high frequency modulation in the AC input power line current. To solve this problem, the MCU

controls the position of the peak current for each phase and centers the secondary phase peak in between

the primary (master) phase peaks.

High Power Two-Phase Digital

Power Factor Correction

Reference Design

Additionally, the MCU-based digital control optimizes the converter’s overall performance including

limiting inrush current, programmable overload protection schemes, and high power factor of conversion,

which gives this device a competitive advantage in high power applications.

Features

The High Power Two-Phase Digital Power Factor Correction reference design offers the following

features:

 Conversion power, maximum: 1.06 kW @120V power line

 Input Voltage: 105 ‒140 V AC 50/60 Hz

 Output Voltage: 400 V ± 2%, programmable

 Output Current: 2.65A @400V

 Output Voltage Ripples: <6% at full load

 Input Current Ripples: <2%

 Load Variation Range: >8x

 Device Conversion Frequency : 100‒120 kHz at high power

 Programmable Overload, Overvoltage, and Brownout Protection

 Digital Inrush Current Control

 Soft Start mode

 Power Good status

Potential Applications

This reference design provides a platform for developing a variety of power management applications

using AC‒DC converters with IXYS power devices and an MCU, including the following applications:

 Medical equipment

 Battery charging

 Air conditioning systems

 High power LED lighting

 Welding equipment

This design may be used at input voltages 220V/240V with minor modifications to the input voltage

sensing schematic providing reference voltages to DAC and MCU measurements. Depending on

customer requirements, MOSFET current sensor gain may also be changed.

Note: The source code file associated with this reference design, IXRD1004-SC01.zip, is available for

download for free from the IXYS Power and Zilog websites (www.ixyspower.com and www.zilog.com).

This source code is tested with ZDS II–Z8 Encore! version 5.2.0. Subsequent releases of ZDS II may

require you to modify the code supplied with this reference design.