DN05032/D Design Note – DN05032/D A 24 Vin, 40 Watt, Low Cost, DC-to-DC Converter Device Application Input Voltage Output Power Topology I/O Isolation NCP1251B NCP431 Instruments, Telecom and Industrial Equipment 20 - 32 Vdc 40 Watts DCM Flyback Yes Other Specification Output 1 Output Voltage Ripple Nominal Current Max Current Min Current 12 Vdc < 2% 3 Amps 3.3 Amps zero Output 2 Output 3 Output 4 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) Minimum Efficiency Inrush Limiting / Fuse Operating Temp. Range Cooling Method / Supply Orientation Signal Level Control No >75% Fuse 0 to 50C Convection NA No Others Input EMI filter Circuit Description This Design Note describes a very simple, low cost, yet high performance dc-to-dc converter using ON Semiconductor’s NCP1251B current mode controller (TSOP6 package) and the NCP431 programmable zener (SOT23 package). The 65 kHz flyback converter design operates in discontinuous conduction mode (DCM) and uses the conventional optocoupler (U2) feedback scheme for the voltage loop. Vcc for the NCP1251 current mode controller is derived directly from the dc input voltage via D2 and R1. The Design Note provides the complete circuit and transformer design details for a 12 volt, 3 amp output version. Other output voltages from 3.3 up to 28 Vdc are easy to implement by modifying the values (or ratings) of R8, R11, R12, C9, D5 and T1’s secondary turns. June 2012, Rev. 0 Over-current limiting is provided by sensing the peak current in the MOSFET Q1 via R6. Once the 800 mV threshold level on U1’s pin 4 is exceeded the circuit will go a “hiccup” mode until the over-current condition is removed. A Vcc OVP circuit is implemented via Z1, while D1 (and fuse F1) provide reverse voltage polarity for the dc input. Depending on the application, it may be necessary to add a small pi-network ripple filter to the output as shown in the lower section of the schematic below. Key Features Input EMI filter (L1, C1) for input EMI compliance Schottky output rectifier for high efficiency Current mode control Small pc board footprint Low cost component www.onsemi.com 1 DN05032/D Schematic1 L1 F1 9,10 10uH, 2.6A 5A 27K 1W C2 C1 0.1uF 100V DC Input R2 R1 1K 220uF 35V T1 MBRS540 C3 10nF 200V 3,4,5 + Q1 D3 R13 10K D5 D4 1N4937 D1 1N5401 + C10 0.1uF 50V C9A C9B C9C 6,7,8 1,2 1000uF, 16V x 3 _ 12V/3A EE25/13/7 R3 Vout 10 D2 MMSD 4148A MMSD 4148A _ R4 R6A/B 10K 0.2 ohm, 1 watt (each) Z1 R5 NCP1251B-65 MMSZ5254B (27V) 3 2 C4 10nF R7 1K C5 1 1K 1nF "Y1" 6 U1 5 R8 1K R10 C11 4 C6 10uF 50V 1nF C8 U3 C7 1nF 27K R12 18K 0.1 R9 U2 4 1 15K NCP431 R11 4.75K 3 2 NOTES: 1. Crossed lines on schematic are NOT connected. 2. U2 is NEC PS2561L-1 or equivalent optocoupler (CTR > 50%). 3. L1 is Wurth 744 772 100 inductor (10 uH, 2.6A) 4. Output caps (C9A/B/C) are radial lead, low impedance types (UCC LXV series or similar). 5. R12 sets Vout. 6. R6A/B sets max output current (0.1 ohms, 2W total for 40Woutput) 7. D1 is for reverse input polarity protection. 8. Q1 is an NTP6410AN on small TO-220 heatsink. 9. See drawing for T1 details. 40 Watt NCP1251B-65 DC/DC Converter (28Vin/65kHz) Rev. 2 Optional Ripple Filter J2 L2 To C10 4.7uH 5A + C13 Vout 100uF _ 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] June 2012, Rev. 0 www.onsemi.com 2 DN05032/D MAGNETICS DESIGN DATA SHEET Project / Customer: ON Semiconductor - 40 watt, 12V/3AV NCP1251 DC-DC Flyback Part Description: 45 watt flyback transformer, 12V/3 amp out, 24 Vdc nominal input Schematic ID: T1 Core Type: EE25/13/7 ferrite core; 3C90 material or similar Core Gap: Gap for 22 uH +/- 10% across primary (pins 1 - 10) Inductance: 22 uH nominal (+/- 10%) on primary Bobbin Type: 10 pin horizontal mount for EE25/13/7 core Windings (in order): Winding # / type Turns / Material / Gauge / Insulation Data Primary (1,2 - 10,9) 12T of 2 strands of #24 mag wire bifilar over 1 layer. Insulate to1 kV to next winding. Self leads to separate pins as shown in schematic below.. 12V Secondary (3,4,5 - 8,7,6) 7 turns of 3 strands of #24 wound trifilar over one layer. Self leads to single pins for each wire as shown in drawing below. Insulate with tape for 1 kV breakdown. Hipot: 1 kV from primary to secondary for 1 minute. Lead Breakout / Pinout Schematic (Bottom View of Bobbin) 9 10 Primary 1 2 June 2012, Rev. 0 3 4 5 10 9 8 7 6 12V sec (trifilar) 0.80" pin rows 6 7 8 1 2 3 4 5 www.onsemi.com 3 DN05032/D References: NCP1251 Data Sheet: http://www.onsemi.com/pub_link/Collateral/NCP1251-D.PDF NCP1250/1251 Application Notes: AND8453/D, AND8468/D, AND8469/D, AND8488/D NCP1251 Design Notes: DN05012, DN05017, DN05028, DN05029 NCP1031 DC-DC Converter Data Sheet: http://www.onsemi.com/pub_link/Collateral/NCP1030-D.PDF NCP1030/1031 Application Notes: AND8119/D, AND8247/D NCP1030/1031 Design Notes: DN06007, DN06046 July 2012, Rev. 0 www.onsemi.com 4