DN06069/D Design Note – DN06069/D Single Stage, Off-line, Isolated 12 Volt, 800 mA Converter with High Power Factor Device Application Input Voltage Output Power Topology I/O Isolation NCP1028 LED lighting, white goods, bias supplies 90 to 265 Vac 10 W nominal DCM Flyback Yes – 3 kV Output Output Voltage Nominal Current Peak Current 12 V 100 to 700 mA 800 mA PFC (Yes/No) Inrush Limiting / Fuse Operating Temp. Range Cooling Method / Supply Orientation Signal Level Control Yes 1 A fuse 0 to +60°C Convection None Others Isolated, step-down conversion with high power factor in a single converter. Since this is a monolithic current mode control chip, the ramp compensation pin was utilized to negate some of the feed-forward effects of current mode control to improve the power factor. Feed-forward pre-regulates off the 120 Hz rectified line ripple which is detrimental to the overall power factor because it prevents true fixed ontime duty ratio through a complete ac line cycle. This is essential for high power factor when using a discontinuous mode (DCM) flyback topology to implement an isolated, single stage PFC converter. Circuit Description This design note (DN) describes an off-line, low power, isolated power supply which has inherent active power factor correction (PFC) integrated into the single stage flyback power topology. This power supply is intended for LED lighting, white goods, industrial, and other applications where a high input power factor is required despite the low power output. For example, Energy Star requires PF > 0.9 for commercial lighting applications; and PF > 0.7 for similar residential lighting applications above 5 watts output. In this design example, the power supply output can provide in excess of 750 mA at 12 volts nominal. Other output configurations are possible by merely changing the transformer design (secondary turns) and the output sensing zener diode (Z1). Details and additional application notes on the NCP1028 monolithic controller can be found at the ON Semiconductor website. For higher power, single stage PFC converters please see information on the NCP1608, NCP1652A, NCL30000, and the NCL30001 controllers. Despite the overall simplicity, one of the drawbacks of incorporating PFC and voltage conversion in a single, isolated power stage is that the feedback loop must have narrow bandwidth (< 40 Hz) otherwise the power factor would be low (capacitor C8 sets the bandwidth). As a consequence, the 120 Hz line ripple is propagated to the output and can only be filtered by the output capacitance. In this example 2,000 uF of output capacitance was adequate to keep the 120 Hz ripple to about 700 mV p/p with a load of 700 mA (~ 6%). Additional output capacitance will reduce it even more. www.onsemi.com Key Features y Simple, low power converter with high input PF y Power factor above 0.9 for 120 vac operation for most typical loads y Inherent over-current and over-temperature protection y Input EMI filter y Easily adjustable for other output voltage/current configurations 1 DN06069/D Schematic F1 L1 3.9 mH 1 A, AC 250 Vac C1 R1 input 1M 10 nF 0.5W "x" D1-D4 MRA4007 T1 C2 10 nF "x" R2 22 C3 0.1uF 400V D6 MBRS360T 10 R3 100K, 1W 1 C4 2.7 nF 2 kV + C7 0.1 C6 C5 6 9 D5 1N4936 R4 10K 5 12 Vdc @ 800mA max _ 1000 uF 16V x2 2 MMSD4148A R12 1.5M R8 10 D7 NCP1028 (100 kHz) 5 3 C10 10 uF 25V C11 1 nF D9 R5 Vtrim (0 ohm) R9 1K R6 U1 MMSD4148A D8 Z1 MMSZ5242B 8 + R11 1.5M 3 2 4 4 R10 39K 7 1 8 U2 1 R7 330 C8 + C9 47 uF 25V 1 uF 47 3 opto 2 NOTES: 1. L1 is Coilcraft E3491-AL common mode EMI inductor (3.9 mH) 2. See Magnetics Data Sheet for T1 construction details (EF-16 core & horizontal bobbin) 3. Z1 zener sets Vout: Vout = Vz + 0.85V; R5 is optional voltage trim (up) resistor 4. R10 sets slope compensation (which optimizes PF) 5. Values of "X" caps C1 & C2 will influence power factor at light loads (more C = lower PF) 6. Crossed schematic lines are not connected 10 Watt, 12 Volt Output Single Stage Power Factor Corrector Supply (Rev 1) 1 © 2010 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] April 2010, Rev. 0 www.onsemi.com 2 DN06069/D MAGNETICS DESIGN DATA SHEET Project / Customer: ON Semiconductor - 10 watt single stage PFC xfmr Part Description: 10 watt NCP1028 DCM PFC transformer, 100 kHz, 12V / 800mA (Rev 1) Schematic ID: T1 Core Type: E24/25 (E25/10/6); 3C90 material or similar Core Gap: Gap for 725 to 775 uH across pins 2 and 10 with pins 1 and 9 connected Inductance: 750 uH +/-5% (across pins 2 and 10 with pins 1 and 9 connected) Bobbin Type: 10 pin horizontal mount for E24/25 (E25/10/6) Windings (in order): Winding # / type Turns / Material / Gauge / Insulation Data Primary A (1 - 10) 25 turns of #30HN over 1 layer. Insulate with tape for 1.5 kV to next winding. Self leads to pins.. Vcc (3 - 8) 5 turns of #30 HN spiral wound over 1 layer with 3 mm end margins minimum. Self leads to pins. Insulate with 1 layer of Mylar tape. 12V Secondary (5 - 6) 5 turns of two pieces of #26 triple insulated wire wound bifilar over previous winding evenly and in 1 layer. Insulate with 1 layer of tape; Self leads to pins. Primary B (2 - 9) Same as Primary A. Hipot: 3 kV from primaries & Vcc to secondary for 1 minute. Lead Breakout / Pinout Schematic (Top View) 10 10 9 8 7 6 1 5 9 2 6 3 12 3 4 5 8 April 2010, Rev. 0 www.onsemi.com 3 DN06069/D Power Factor and Efficiency versus Load Plots PF versus Iout 1 Power Factor 0.95 120 Vac 0.9 230 Vac 0.85 0.8 0.3 0.4 0.5 0.6 0.7 Output current (amps) 1 Efficiency % versus Iout 81 Efficiency (%) 80 79 Eff -120Vac 78 Eff - 230Vac 77 76 75 0.3 0.4 0.5 0.6 0.7 0.8 Output current (amps) 1 © 2010N 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] April 2010, Rev. 0 www.onsemi.com 4 DN06069/D 120 Hz Output Ripple 700 mA Load; Cout = 2000 uF (2 volts per division vertical) 350 mA Load; Cout = 2000 uF 1 © 2010 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] April 2010, Rev. 0 www.onsemi.com 5