DN06064/D Design Note – DN06064/D 12 Watt “Mini” Boost Power Factor Corrector Device Application Input Voltage Output Power Topology I/O Isolation NCP1014 PFC Circuit for Low Power Lighting Applications 90 to 265 Vac 12 Watts DCM Boost None Output 1 Output Voltage Ripple Nominal Current Max Current Min Current 400 Vdc +/- 5% < 10% 30 mA @ 400 Vdc 36 mA surge zero Yes 85 - 90% Optional 0 to +60˚C Convection PFC (Yes/No) Nominal Efficiency Inrush Limiting / Fuse Operating Temp. Range Cooling Method / Supply Orientation Signal Level Control NA Introduction This Design Note contains a very simple yet effective design for a “mini” off-line, boost power factor corrector (PFC) circuit with a nominal output of 12 watts and a peak capability of 14 watts. The output voltage is set at the typical 400 Vdc level as would be required by an isolated “down stream” dc-to-dc converter, but can be adjusted to a lower voltage value via resistor R5 to fit the specific application. The intended use of this PFC circuit is to drive an isolated, off-line dc-to-dc converter that is designed to provide power to commercial lighting applications (or similar) where a power factor of 0.9 or greater is still required for power levels of 14 watts and below. Circuit Description The circuit design is implemented as a discontinuous conduction mode (DCM) boost converter PFC utilizing ON Semiconductor’s NCP1014 monolithic current mode controller with internal MOSFET. Unlike a conventional dc-dc boost converter, this circuit has low input capacity (C3) after the input bridge rectifier BD1. This is to minimize the effect of the normally large bulk September 2009, Rev. 1 capacitor on the power factor at the input. The fullwave rectified ac haversine is presented directly to the converter’s input boost choke L2. A simple input EMI filter comprised of C1, C2 and L1 is included to help attenuate conducted RFI line emissions. Signal level MOSFET Q1 functions as an error amplifier to sense the output voltage via resistor divider R4/R5 and drive the feedback pin of U1, the NCP1014. The sense level threshold is just the gate threshold of the VN2222 MOSFET and Vout can be set by adjusting the ratio of resistors R4/R5. Because the control chip U1 operates in current mode by sensing the peak internal MOSFET current, R2 is required to inject a sample of the rectified ac line haversine envelope to improve the power factor by modulating the feedback signal and neutralizing some of the feed-forward effect caused by the current mode control algorithm. In addition, ac feedback capacitor C7 is necessary to provide a small amount of phase shift and band width reduction to allow a decent power factor at the high end of the line voltage range. Since the controller has an internal Vcc supply (DSS), no aux winding on the boost choke L2 is necessary. www.onsemi.com 1 DN06064/D The power factor (PF) is maintained above 0.9 from 90 to 240 Vac from roughly half-load to max load at 14 watts (see table on page 4). Although the power factor for typical loads meets Class C for commercial lighting standards, the harmonic content is higher than would be if the input were a pure sine wave (see line current plots page 4 & 5). At power levels below 25 watts, however, these harmonic levels are below the agency specified levels, so the trapezoidal line current wave shape is inconsequential as long as the PF is greater than 0.9. If the circuit is tailored for voltages less than 400 Vdc output, components R2 and C7 can probably be modified for additional optimization of the power factor. Key Features y Extremely simple yet effective boost PFC circuit for low power “downstream” converters. y Uses essentially “off-the-shelf” components. y Inherent overcurrent and undervoltage protection in NCP1014 (U1). y High efficiency and good power factor for low power level. September 2009, Rev. 1 www.onsemi.com 2 DN06064/D Schematic R1 90 - 260 Vac input C1 3.3, 2W 0.1uF "x" L1 820uH BD1 1A 600V C2 10nF 250V C3 0.1uF 250V L2 1.8 mH R2 D1 + 1.8M, 0.5W MURS160 NCP1014 (100 kHz) U1 Gnd 4 3 2 1 D FB R3 1K Vcc R4 2M, 0.5W C6 400 Vdc Output, 14 W max 10uF 450V C7 47nF + C4 220uf 16V C5 Q1 1nF VN2222 R5 9.1K _ Notes: 1. Crossed lines on schematic are not connected. 2. L1 is Coilcraft RFB0807-821L (820 uH, 320 mA) 3. L2 is Coilcraft RFB1010-182L (1.8 mH, 450 mA) 4. R5 sets Vout September 2009, Rev. 1 www.onsemi.com 3 DN06064/D Test Results (Vout nominal = 400 Vdc) y Load Regulation (3.5 to 14 watts): 4% y Line Regulation (90 to 260 Vac, 8 watts out): 5% y Power Factor and Efficiency Measurements: Pout = 14 W 8W 3.5 W 120 Vac in PF Efficiency 0.97 88% 0.95 86% 0.90 83% 230 Vac in PF Efficiency 0.95 92% 0.91 91% 0.75 85% Measurements Output Voltage and Ripple at 12 Watt Output Vout during Startup with 120 Vac Input and 12 W Output September 2009, Rev. 1 Vout during Startup with 230 Vac Input and 12 W Output www.onsemi.com 4 DN06064/D 1 Line Current at 12 Watt Load and 120 Vac Input Line Current at 12 Watt Load and 230 Vac Input References: y ON Semiconductor Design Note DN06051: Improving the Power Factor of Isolated Flyback Converters for Residential ENERGY STAR® LED Luminaire Power Supplies y ON Semiconductor Application Note AND8123: Power Factor Correction Stages Operating in Critical Conduction Mode y ON Semiconductor Application Note AND8353: Implementing Cost Effective & Robust Power Factor Correction with NCP1607 y ON Semiconductor PFC Handbook HBD853 1 © 2009 ON Semiconductor. Disclaimer: ON Semiconductor is providing this design note “AS IS” and does not assume any liability arising from its use; nor does ON Semiconductor convey any license to its or any third party’s intellectual property rights. This document is provided only to assist customers in evaluation of the referenced circuit implementation and the recipient assumes all liability and risk associated with its use, including, but not limited to, compliance with all regulatory standards. ON Semiconductor may change any of its products at any time, without notice. Design note created by Frank Cathell, e-mail: [email protected] September 2009, Rev. 1 www.onsemi.com 5