DN05029/D Design Note – DN05029/D A 12 Volt, 30 Watt, Off-line Mini-Forward Converter Device Application Input Voltage Output Power Topology I/O Isolation NCP1251B NCP431 NDD04N60 White Goods, Small Instruments, EMeters, Industrial Equipment 90 – 267 Vac 30 Watts RCD Reset Forward Converter 3 kV Other Specification Output Voltage Ripple Nominal Current Max Current Min Current Output 1 Output 2 Output 3 Output 4 12 Vdc < 1% 2.5 Amps 3 Amp surge zero N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A PFC (Yes/No) Efficiency Inrush Limiting / Fuse Operating Temp. Range Cooling Method / Supply Orientation Signal Level Control No 84% at full load Yes 0 to 50C Convection NA No Others Input EMI filter Circuit Description This Design Note describes a simple, low cost, high performance, off-line forward converter power supply using ON Semiconductor’s NCP1251B flyback controller (TSOP6 package), NDD04N60 D-Pak Mosfet, and the NCP431 programmable zener (SOT23 package). This design is an extension of the “mini-forward” converter design described in ON Semiconductor’s Application Note AND8489 in which the NCP1028 monolithic switcher was used as the main controller. topology. This design is particularly useful in Emeter and white goods applications where a higher output power is required but low ripple/noise and high efficiency are imperative. In addition, all of the various features of the NCP1251current mode controller can be utilized as needed. The output inductor is an off-the-shelf part (Coilcraft) and the transformer is the same as that used in AND8489 and is available from Wurth Electronics (see drawing below). Key Features The use of an RCD snubber reset type of forward converter allows the extension of the useful duty cycle to over 50% without excessive voltage excursions across the MOSFET. The topology provides lower output ripple and noise, lower EMI generation, and slightly higher efficiency than an equivalent 12V/2.5A flyback Rev 0, May, 2012 Input EMI filter for conducted EMI compliance Low Vf Schottky rectifier for high efficiency Low standby (no load) power Current mode control with adjustable output voltage and current limit setpoints 5V/6A version also designed and tested. www.onsemi.com 1 DN05029/D Forward Converter Schematic 1 J1 R1 L1 3.9 mH 4.3, 5W D1-D4 MRA4007 C2 C1 90 - 265Vac 100nF Input "x" F1 L2 470 uH R2 2.2M 0.5W 100nF "x" T1 C3 C4 10 uF, 400Vdc 1.5 A, 250 Vac 47K, 1W 47uF 400V 2.2nF 2 kV NDD04N60 Q1 R8 470K R9 470K 10K D6 1N4937 3 1 9 2 + C7 10nF R11 1K C14 12V, 2.5A 0.1 _ 10 5 1nF "Y1" 6 4 R10 D7 2.2K MMSD 4148A R14 1K R15 10K 2 MMSZ 5252B 1000uF 16V + C11 U1 Z1 C13 R13 43 7 3 4 U2 3 opto 1 R12 C8 4.7uF 35V D8 4 1.0 0.5W NCP1251B1 5 390pF 100uH NTSB2011CT R6 R7 J2 C12 R4 C5 D5 MRA4007 L3 1 R3 10 C9 1nF 1K + C10 220pF C6 1 uF, 100V 2 U3 R16 C15 47K 0.1 NCP431A R17 20K R18 5.1K NOTES: 1. L1 is Coilcraft E3491-AL common mode EMI inductor ( 3.9mH) 2. L2 is Wurth 744772471 (470 uH) or similar 3. L3 is Coilcraft PCH-45X-104LT (100uH, 2.8A) inductor 4. R10 sets slope compensation. 5. R12 value dependent on Vout and Vcc winding turns. 6. R17 sets Vout (R17/18 node is set to 2.5V) 7. R6 sets current limit level. 8. R1 is optional inrush limiter. 9. U1 optocoupler is Vishay SFH6156A-4 or similar. 10. Crossed schematic lines are not connected. 11. Heavy schematic lines are recommended ground plane areas. 30 Watt, 12 Volt Output NCP1251 Single Switch Forward Converter 1 © 2012 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] Rev 0, May, 2012 www.onsemi.com 2 DN05029/D MAGNETICS DESIGN DATA SHEET Project / Customer: ON Semiconductor - 30 watt, 12 vout NCP1251 Fwd Conv Part Description: 30 watt resonant reset forward conv. xfmr (Rev 1) Schematic ID: T1 Core Type: EF25 (E25/13/7); 3C90 material or similar Core Gap: No gap Inductance: (Primary) 12 mH minimum Bobbin Type: 10 pin horizontal mount for EF25 Windings (in order): Winding # / type Turns / Material / Gauge / Insulation Data Primary A (1 - 2) 50T of #28HN over 2 layers (25 TPL). Insulate for 1 kV to next winding. Self leads to pins. Vcc (4 - 5) 14 turns of #28 HN over 1 layer, close wound and centered in window. Self leads to pins. Insulate to 3 kV to next winding 12V Secondary (9 - 7) 20 turns of #24 triple insulated wire over one layer. Self leads to pins. Primary B (2 - 3) Same as Primary A. Insulate with tape and selfleads to pins. Hipot: 3 kV from primaries & Vcc to secondary for 1 minute. Lead Breakout / Pinout Schematic 1 (Top View of Bobbin) Pri A 2 10 9 8 7 6 9 12V sec Pri B 0.20" pin separation (8 places) 0.80" 7 3 4 1 2 3 4 5 Vcc 5 Transformer is available from Wurth Electronics as part number 750312228 Rev 0. Rev 0, May, 2012 www.onsemi.com 3 DN05029/D Efficiency Plots References: ON Semiconductor Data Sheet for NCP1251 controller. ON Semiconductor Application Note AND8489/D ON Semiconductor Design Notes DN05012 and DN05028