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| Design Idea DI-20 (R) TOPSwitch-GX 145 W PC Main ATX Supply Application PC Main Device TOP247 Power Output 145 W Input Voltage 90-130 VAC / 180-265 VAC Output Voltage 3.3 V / 5 V / 12 V Topology Forward (R) Design Highlights * 145 W cont. (160 W peak) in PC ATX form factor * TOPSwitch-GX integrated features enable extremely low component count * Meets 1 W standby spec. (0.91 W input 0.5 W output) * High efficiency (71% minimum) * Integrated line undervoltage and overvoltage detection * Low EMI due to frequency jitter * SOURCE referenced TO-220 tab lowers conducted EMI * Maximum duty cycle (DCMAX) reduction prevents transformer saturation for fault and transient loads * Uses conventional magamp for 3.3 V output * Meets CISPR22B/EN55022B conducted EMI only as needed to minimize zero-load power consumption. Resistors R3, R5 and R6 implement start-up undervoltage lockout, which prevents the supply from starting below 180 VDC. Components R4, R14, Q1 and R30 implement an independent undervoltage using the X pin, which allows the supply to continue delivering power all the way down to 140 VDC (increasing hold-up time). Resistor R7 provides additional hysteresis. The primary side components D1, VR3-5 and C4, along with secondary side C9 and R30, implement the Zener/capacitor reset/clamp circuit. This circuit provides reset voltage for the transformer and clamps the DRAIN pin voltage to a safe level (<~600 V) under all conditions. The reset circuit works in conjunction with the DCMAX reduction circuit (R8, R36, C22, VR19 and D18) to limit the maximum duty cycle and prevent transformer saturation under fault and transient conditions. C10 1 nF 50 V 4 Coupled choke L1 13 H Operation TOPSwitch-GX integrates many features designed for use with forward converters. Transistors Q4, Q6, R1, R2, R3, R5 and R6 form an active capacitor (C2, C3) balancing circuit, operating 3 1, 2 C11 1000 F 16 V R1 330 k C4 2.2 nF 1 kV D1 1N5407 1 R3 2.2 M R4 2.2 M R5 180 k 5 14 D7 MBR3045 13 R30 1 1W 8, 9 D8 MBR6045 C9 47 nF 50 V +12 V L2 0.5 H +5 V 5, 6 BR1 KBL06 CY3 2.2 nF (Safety) JP9 CX1 0.047 F 250 VAC L7 8.2 mH CX2 0.33 F 250V RT1 10 R10 560 K 1/2 W CY4 2.2 nF (Safety) C2 330 F 200 V Q4 MPSA42 C12 2200 F 6.3 V R6 2.2 M 11,12 7 C20 330 pF 50 V R21 270 C13 220 F 63 V TO MAGAMP (3.3 V) RTN TOPSwitch-GX U1 TOP247 To AC Selector Switch Q6 MPSA92 R8 130 k 1% D L CONTROL C R13 10 D6 BAV20 D18 BAV20 R36 43.2 k 1% C22 100 pF 50 V R7 560 k 3 C5 1 F 100 V R18 4.74 k 1% C17 100 nF 50 V U2 SFH615A-2 R16 1 k R15 1.8 k R20 270 k C3 330 F 200 V VR3 BZY97C200 VR4 BZY97C180 VR5 R2 BZY97C330 k 180 VR19 1N5229 S X F C8 0.033 F 50 V R9 47 C6 47 F 16 V R11 300 Q1 2N3908 R14 75 k D105 1N4148 U5 TL431 C16 100 nF R17 50 V 15 k RV1 275 V, 14 mm R30 3.3 k R19 4.12 k 1% PI-3165-120902 R12 12 k +12 V STBY R38 5.1 k U3 LTV817 R106 27 k Remote ON/OFF R37 10 k F1 4A L G N C7 100 nF 50 V Q7 2N3904 C23 33 nF 50 V Figure 1. 145 W (160 W pk.) PC Main Power Supply Schematic (Note: Schematic does not include transformer Y-capacitor). DI-20 www.powerint.com December 2002 DI-20 The components R12, C7, R38, Q7, C23, R37, U3, R106 and D105 implement the remote ON/OFF drive circuit. During the ON state, U3 and hence Q7 conduct pulling the X pin to SOURCE via resistor R12 (which sets the current limit). During the OFF state, U3 and Q7 are off, allowing the X pin to be pulled high by the +15 V standby supply via R38 and R12 and putting the TOPSwitch-GX into the OFF state. Components R38 and D105 reduce device consumption to around 2 mW by supplying external current to the CONTROL pin from the +15 V standby supply. Resistor R11 is required to allow external bias feed. * Maintain maximum flux density on transformer (T1) < 2500 gauss * Check for balanced currents on coupled inductor (L1), for all load combinations * Use PI Expert (PIXls) Design Spreadsheet and refer to Application Note AN-30, for details on designing forward converters with TOPSwitch-GX Due to the complexity of this design it is not possible to include all details in this Design Idea. For detailed design information on the PC Main please refer to Design Accelerator Kit (DAK-12) and Engineering Prototype Report EPR-12. For all other information please refer to Power Integrations' Web site. Key Design Points * Transformer reset: Use recommended Zener/capacitor clamp/reset circuit to maintain drain voltage <600 V and DCMAX reduction to prevent transformer saturation. D9 MBR2045 FROM MAIN CONVERTER 5 V WINDING L3 Mag Amp 6 Turns L4 20 H R22 3 Q2 TIP32 R34 33 L5 0.5 H 3.3 V R23 1 k R27 390 C21 1 F 50 V C18 0.1 F 50 V U8 TL431 R25 2.7 k R24 3.84 k 1% C14 1200 F 10 V C15 1200 F 10 V D11 UF4002 RTN D10 UF4002 R26 10 k 1% RTN PI-3385-093002 Figure 2. Magamp for Independent 3.3 V Secondary Regulation. For the latest updates, visit our Web site: www.powerint.com Power Integrations reserves the right to make changes to its products at any time to improve reliability or manufacturability. Power Integrations does not assume any liability arising from the use of any device or circuit described herein, nor does it convey any license under its patent rights or the rights of others. 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 and EcoSmart are registered trademarks of Power Integrations, Inc. PI Expert is a trademark of Power Integrations, Inc. (c)Copyright 2002, Power Integrations, Inc. WORLD HEADQUARTERS AMERICAS Power Integrations, Inc. San Jose, CA 95138 USA Customer Service: Phone: +1 408-414-9665 Fax: +1 408-414-9765 e-mail: usasales@powerint.com CHINA Power Integrations International Holdings, Inc. China Phone: +86-755-8367-5143 Fax: +86-755-8377-9610 e-mail: chinasales@powerint.com EUROPE & AFRICA Power Integrations (Europe) Ltd. United Kingdom Phone: +44-1344-462-300 Fax: +44-1344-311-732 e-mail: eurosales@powerint.com KOREA Power Integrations International Holdings, Inc. Seoul, Korea Phone: +82-2-782-2840 Fax: +82-2-782-4427 e-mail: koreasales@powerint.com SINGAPORE Power Integrations, Singapore Republic of Singapore 308900 Phone: +65-6358-2160 Fax: +65-6358-2015 e-mail: singaporesales@powerint.com JAPAN Power Integrations, K.K. Keihin-Tatemono 1st Bldg. Japan Phone: +81-45-471-1021 Fax: +81-45-471-3717 e-mail: japansales@powerint.com APPLICATIONS HOTLINE World Wide +1-408-414-9660 TAIWAN Power Integrations International Holdings, Inc. Taipei, Taiwan Phone: +886-2-2727-1221 Fax: +886-2-2727-1223 e-mail: taiwansales@powerint.com INDIA (Technical Support) Innovatech Bangalore, India Phone: +91-80-226-6023 Fax: +91-80-228-9727 e-mail: indiasales@powerint.com APPLICATIONS FAX World Wide +1-408-414-9760 B 12/02 www.powerint.com |
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