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| Design Idea DI-23 (R) TOPSwitch-GX 10 W, Multi-output, High Speed Modem Power Supply Application High Speed Modem Device TOP243P Power Output 10 W Input Voltage 85-264 VAC Output Voltage 3.3 V / 5 V / 30 V Topology Flyback Design Highlights * Compact low cost design (113 mm x 39 mm x 25 mm) with only 46 parts * Meets Blue Angel no-load power consumption * Line undervoltage protection prevents turn-off output glitches and overvoltage protection provides extended line surge protection * Hysteretic thermal shutdown provides automatic fault recovery * Frequency jittering dramatically reduces EMI and meets EN550022 Class B without Y1 capacitor * Ultra low leakage current (<1 A at 265 VAC) eliminates audio hum in voice applications * Surge immunity to 4 kV (EN61000-4-5) * High efficiency >70% Typical applications are wall mount adapters, set-top box, highspeed modem, standby power supplies, and other applications requiring very low cost, small size, and low no-load input power consumption. The example discussed here passes EMI conducted and radiated emissions tests without using a Y1 capacitor between primary and secondary. This is possible with the frequency jittering feature of TOPSwitch-GX and careful transformer construction. Shield windings are used in the transformer to reduce common mode EMI currents. Transformer specifications are given in Table 1. Good cross-regulation of output voltages is achieved by careful transformer construction and using a TL431 voltage regulator instead of a Zener regulator. The power supply uses a low cost RCD clamp with a slow 1N4007GP diode, which reduces EMI emissions and recycles leakage energy, increasing efficiency. Input line sensing prevents reverse conduction of current in TOPSwitch-GX at very low input voltages due to the 1N4007GP in the RCD clamp. Operation TOP243P (DIP package) is shown in Figure 1. The power supply utilizes many TOPSwitch-GX features such as frequency jittering, input voltage sense, thermal shutdown, internal current limit, soft-start, etc. without adding any extra components. D7 UF4003 10 C2 1 nF 1 kV R1 150 k 0.5 W 9 2 6 R6 100 D5 1N4007GP C1 33 F 400V C13 2.2 nF R8 10 D8 SB360 D9 SB540 1 R5 10 C4 47 F 50 V C5 820 F 16 V C6 820 F 16 V C7 820 F 16 V L4 10 H L2 3.3 H L3 3.3 H C9 150 F 6.3 V R6 75 U2 LTV817A R7 R10 1 k 15.4 k 1% C10 0.1 F R11 10 k 1% C8 100 F 10 V C10 10 F 50 V R13 12 k 0.03 A, 30 V 0.9 A, 5 V D1-D4 1N4007 1 A, 1000 V 1.5 A, 3.3 V 7 4 5 R2 2 M TOPSwitch-GX M CONTROL C RTN L1 20 mH 0.8 A C15 0.1 F 250 VAC X2 D6 1N4148 C11 0.1 F T1 EE25 D F1 3.15 A U1 TOP243P S R4 6.8 C3 47 F 10 V C14 1 F 50 V L 85 - 265 VAC U3 LM431BCZ 1% R12 10 k 1% PI-3366-120704 N Figure 1. TOP243P - 10 W, 3.3 V at 1.5 A, 5 V at 0.9 A, 30 V at 0.03 A, High Speed Modem Power Supply. DI-23 www.powerint.com December 2004 DI-23 Key Design Points * Use KRP (Ripple-to-peak current ratio) in the range of 0.4-0.6 for better efficiency. * Select VOR (reflected output voltage) of 90 V to 110 V for optimum performance. * Opto with CTR range of 80% to 160% recommended. * PCB traces which carry high switching voltages and current should be short and wide to reduce EMI. * Reduce leakage inductance and improve cross-regulation by filling each winding layer across the entire width of the bobbin. * Use shield windings to improve EMI. * Use a layer of insulation tape between layers of primary winding to reduce inter-winding capacitance. * D5 should be a GP type (glass passivated) to ensure a controlled reverse recovery time. TRANSFORMER PARAMETERS Core Material Bobbin EE25, Nippon Ceramic NC-2H or equivalent, ALG = 351 nH/T2 YW-360-02B, YIH-HWA, 10 pin Vertical Shield: 15T, 2 x 29 AWG Primary: 49T, 27 AWG Bias: 7T, 3 x 28 AWG 3.3 V: 2T, 3 x 26 AWG T.I.W. 5 V: 1T, 26 AWG T.I.W. 30 V: 13T, 26 AWG T.I.W. (T.I.W. = Triple Insulated Wire) Shield (1-NC), 3 x tape, Primary (2-1), with tape between layers, tape, Bias (5-4), 6 x tape, 3.3 V (6-7), tape, 5 V (9-6), tape, 30 V (10-9), 2 x tape, Shield (1-3), 3 x tape Primary: 1 mH 10%, Leakge: 30 H (maximum) 500 kHz (minimum) VO 3.3 5 30 Load Regulation (%) Range -8 -7 -6 -5 -4 -3 -2 -1 0 1 2 3 4 5 6 7 8 9 10 (Amp) 0.3-1.5 0.3-0.9 0.01-0.03 Table 2. Worst Case Output Cross-Regulation - Outputs Taken from Minimum to Maximum Load. PI-3370-091502 Winding Details 80 70 60 50 40 QP AV Quasi Peak dBV Winding Order (Pin Numbers) 30 20 10 0 -10 -20 0.15 1.0 10.0 130.0 Average Inductance Primary Resonant Frequency Table 1. Transformer Construction Information. MHz Figure 2. Conducted Emissions - EN55022 Class B (QP and AV), 230 VAC, Full Load, Artificial Hand Connected to Secondary Return. For the latest updates, visit www.powerint.com Power Integrations may make changes to its products at any time. Power Integrations has no liability arising from your use of any information, device or circuit described herein nor does it convey any license under its patent rights or the rights of others. POWER INTEGRATIONS MAKES NO WARRANTIES HEREIN AND SPECIFICALLY DISCLAIMS ALL WARRANTIES INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE, AND NON-INFRINGEMENT OF THIRD PARTY RIGHTS. The products and applications illustrated herein (including circuits external to the products and transformer construction) may be covered by one or more U.S. and foreign patents or potentially by pending U.S. and foreign patent applications assigned to Power Integrations. A complete list of Power Integrations' patents may be found at www.powerint.com. The PI logo, TOPSwitch, TinySwitch, LinkSwitch, DPA-Switch and EcoSmart are registered trademarks of Power Integrations. PI Expert and PI FACTS are trademarks of Power Integrations. Copyright 2004, Power Integrations Power Integrations MAIN PHONE NUMBER +1 408-414-9200 C 12/04 5245 Hellyer Avenue APPLICATIONS FAX +1 408-414-9760 San Jose, California 95138 For a complete listing of worldwide sales offices, please visit www.powerint.com APPLICATIONS HOTLINE +1 408-414-9660 www.powerint.com |
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