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| Design Idea DI-31 TM DPA-Switch 5 V, 70 W DC-DC Converter with Synchronous Rectification Application DC-DC Converter Device DPA426R Power Output 70 W Input Voltage 36-75 VDC Output Voltage 5V (R) Topology Forward Design Highlights * * * * * * Extremely low component count High efficiency, 90% using synchronous rectification No current sense resistor or current transformer required Output overload, open loop and thermal protection Accurate input under/overvoltage meets ETSI standards 300 kHz switching frequency - optimizes efficiency using Capacitor C9, diodes D1-D2, and inductor L2 form a resonant simple self-driven synchronous rectification snubber that recycles leakage and magnetizing energy stored in T1, and also helps to reset T1. Zener diode VR1 provides a hard voltage limit and only conducts during output transient Operation and overload conditions. Capacitor C12 and Resistor R7 The 70 W converter shown in Figure 1 benefits from many of damp secondary switching spikes and help to reset T1. the DPA-Switch integrated features. In particular, no external current sense components are required. In a discrete implementation, an expensive current transformer and a number Key Design Points of additional components would increase the cost of this * For nominal undervoltage set point V : UV converter significantly. R1 = (VUV - 2.35 V)/50 A. VOV = (R1 x 135 A) + 2.5 V. * Locate C10, C11, and R3 close to the U1 CONTROL pin, R1 programs the input UV/OV thresholds. The tight tolerance with ground connections returned to SOURCE pin. of the UV/OV thresholds limits the range of gate drive voltages C7 1 nF 1.5 kV + VIN 36-75 VDC L1 1 H 2.5 A 1 applied to MOSFETs Q1 to Q6, eliminating the need for gate voltage clamp circuitry. The self-driven synchronous rectification configuration is therefore very simple, with R4 to R6 filtering voltage spikes at the gates of Q1, Q2 and Q3 and D4 preventing the body diodes of Q4, Q5 and Q6 from conducting. T1 9,10 R4-R6 10 Q4-Q6 SI4842DY L3 3.8 H 20 A C13, C14, C15, C16, C17 100 F 10 V (x5) L4 100 nH 20 A C18, C19 100 F 10 V 5 V, 14 A C20 1 F 10 V RTN D1 ESD1 R1 619 k 6,7 2 D4 Q1-Q3 42CTQ30S SI4842DY C12 2.2 nF, 50 V R7 1 U2 3 C1, C2 1 F 100 V C3, C4, C5, C6 1 F 100 V (x4) C9 150 pF 200 V 5 4 D L CONTROL CONTROL L5 D3 2.2 mH BAV19WS 40 mA D5 BAV19WS C8 1 F 25 V R13 10 k D6 BAV19WS R15 10.0 k 1% C22 100 nF R10 5.1 R14 220 C21 1 F DPA-Switch C L2 220 H S U1 DPA426R R11 150 U2 PC357N1T C23 10 F 10 V U3 LM431AIM3 X F -VIN VR1 SMBJ 150 D2 ESD1 R3 1.0 C10 220 nF R2 6.8 k 1% C11 68 F 10 V R16 10.0 k 1% PI-3375-121602 Figure 1. DPA426 70 W, 5 V, 14 A DC-DC Converter. DI-31 www.powerint.com December 2002 DI-31 * Minimize primary and secondary high current loop areas to reduce parasitic inductance. * Optocoupler U2 should have a controlled CTR range of 100 to 200% for optimum loop stability. * Size transformer reset components to ensure transformer reset at minimum operating voltage without exceeding 170 V drain voltage at high line. It may be necessary to gap T1 to offset effect of Q4-Q6 gate capacitance. * Set Zener VR1 clamp voltage to 150 V to both safely limit the DRAIN below BVDSS and guarantee transformer reset. * Select number of bias turns to provide 12 V to 14 V at minimum input voltage and full load. * Main primary power return should be connected to the DPA-Switch tab, not to the SOURCE pin. * Scale time constant of C9 and L2 to allow C9 to reset completely during minimum on-time conditions. * Consult AN-31 for additional design tips and information. PI-3376-091502 TRANSFORMER PARAMETERS Core Material Bobbin EFD25, 3F3 Gap for ALG = 1100 nH/T2 EFD25 10 pin (B&B B-025 or equivalent) Bias: 5T, 30 AWG Primary: 6T+ 5T, 4 x 26 AWG Secondary: 3T, 0.005" Cu foil Primary (3-2), tape, Bias (4-5), tape, Secondary (6,7-9,10), tape, Primary (2-1), tape Primary: 130 H 10%, Leakge: 10 H (max) 3 MHz (minimum) Winding Details Winding Order (Pin Numbers) Inductance Primary Resonant Frequency Table 1. Transformer Design Parameters. 92 90 OUTPUT INDUCTOR PARAMETERS Core Bobbin Winding Details EE22, TDK PC40 Material Gap for ALG of 250 nH/T2 TDK BE-22-5116 4T, 0.016" Cu foil 4 H 10% Efficiency (%) 88 86 84 82 80 VIN = 36 VDC VIN = 48 VDC VIN = 60 VDC VIN = 72 VDC Inductance Table 2. Output Inductor Construction Information. 80 0 20 40 60 Output Power (W) Figure 2. Efficiency vs. Output Power. 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 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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