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| Design Idea DI-57 TM DPA-Switch 60 W DC-DC Converter Application Telecom Device DPA426R Power Output 60 W Input Voltage 36-75 VDC Output Voltage 12 V Topology Flyback (R) Design Highlights * * * * * * * Low cost 400 kHz flyback design Simple Zener referenced 12 V output Efficiency - 82% at 36 VDC and full load Low component count Accurate line OV and UV protection Thermal, short circuit and output overload protection No current sense components minimize fault and overload power. Drain voltage clamping is provided by diode D4 and Zener diode VR1 with optional components C4 and R2 to provide high frequency snubbing. The output is rectified by diode D2 with optional high frequency damping from components C9, R15 and R16. The output capacitors are alternated to share the ripple current evenly between the Oscon capacitors (C10-14) and the ceramic capacitors (C15-C18). A final decoupling ceramic capacitor C19 is placed at the output pins of the power supply. Output regulation is taken from the +12 V output. Zener diode VR2 is DC-biased by resistor R7 with the opto-diode of U2 providing feedback and resistor R6 programming the gain. Optional capacitor C8 implements a soft-finish network to slow the rise of the output voltage at start-up. R15, R16 33 1/4 W Operation DPA-Switch greatly simplifies the design compared to a discrete implementation. Resistor R1 programs the under/over voltages and linearly reduces the maximum duty cycle with input voltage to prevent core saturation during load transients. Resistor R3 programs the DPA-Switch current limit at 85% of nominal to C7 1 nF 1.5 kV + VIN L1 36-75 VDC 1 H, 2.5 A 2 R14 10 T1 9,10 C9 2.2 nF 50 V C10-C14 100 F, 16 V (OSCON) C19 1 F 16 V 12 V, 5 A VR1 SMCJ 100 A NC 6,7 D2 SBG3045CT D1 BAV19WS C15-C18 47 F, 16 V (CERAMIC) RTN D4 ES2D 4 1 5 C23 4.7 F 20 V U2 R7 U2 1 k R1 619 k 1% C1 1 F 100 V C2 1 F 100 V C3 1 F 100 V C4 180 pF 200 V PC 357N1T DPA-Switch U1 DPA426R D L CONTROL R6 150 C S X F R2 68 1/4 W -VIN R3 8.8 k C5 1% 220 nF R4 1.0 C6 68 F 10 V C8 1 F 16 V VR2 BTZ52C11 Figure 1. DPA426R - 60 W, 12 V, 5 A DC-DC Converter. DI-57 PI-3662-082603 www.powerint.com August 2003 DI-57 The bias winding is rectified and filtered by D1 and C23 and provides operating power to the DPA-Switch. The regulation is fed back from the secondary through the opto-transistor of U2. TRANSFORMER PARAMETERS Core Material Bobbin Ferroxcubed P/N: EFD25 3F3 10-pin EFD25 surface mount bobbin Primary 8T + 8T, 2 x 24 AWG Bias 5T, 1 x 34 AWG +12 V 5T, 4 x 27 AWG Primary-1 (4-NC), Bias (1-5), + 12 V (9, 10-6, 7), Primary-2 (NC-2) 21 H 25% (at 400 kHz) 3.0 MHz (minimum) 1 H (maximum) Key Design Points * For the nominal under-voltage set point VUV: R1 = (VUV - 2.35) / 50 A VOV = (R1 x 135 A) + 2.5 V * For highest efficiency designs: use continuous conduction mode operation, this design uses approximately 0.5 KRP; minimize turns in the transformer and at this (60 W) power level, keep AC flux density BM < 1100 Gauss; fully fill a single layer for each winding to minimize leakage inductance and maximize copper fill factor; if possible use a Schottky rectifier diode (D2) with a low-forward drop. * The transformer primary is split in order to minimize leakage inductance to obtain better efficiency. * Tighter output voltage tolerance is possible by using a TL431 (and associated components) in place of the Zener diode VR2. * Follow good layout practices: - For length of the secondary current loop from transformer pins 9 & 10, diode D2 and capacitors C10 to C18 and back to pins 6 & 7 of the transformer: ensure identical path length for each of the capacitors C10 to C18 to ensure they equally share the ripple current. Winding Details Winding Order and Pin Numbers Primary Inductance Primary Resonant Frequency Leakage Inductance Table 1. Transformer Design Parameters. 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 and DPA-Switch are trademarks of Power Integrations, Inc. (c)Copyright 2003, Power Integrations, Inc. WORLD HEADQUARTERS San Jose, CA USA. Customer Service: Phone: +1-408-414-9665 Fax: +1-408-414-9765 e-mail: usasales@powerint.com AMERICAS Buford, GA USA Phone: +1-678-714-6033 Fax: +1-678-714-6012 e-mail: usasales@powerint.com CHINA (SHANGHAI) Shanghai, China Phone: +86-21-6215-5548 Fax: +86-21-6215-2468 e-mail: chinasales@powerint.com APPLICATIONS HOTLINE World Wide +1-408-414-9660 A 8/03 CHINA (SHENZHEN) Shenzhen Guangdong, China Phone: +86-755-8367-5143 Fax: +86-755-8377-9610 e-mail: chinasales@powerint.com GERMANY Muenchen, Germany Phone: +49-895-527-3910 Fax: +49-895-527-3920 e-mail: eurosales@powerint.com INDIA (TECHNICAL SUPPORT) 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 ITALY Milano, Italy Phone: +39-028-928-6001 Fax: +39-028-928-6009 e-mail: eurosales@powerint.com JAPAN Kanagawa, Japan Phone: +81-45-471-1021 Fax: +81-45-471-3717 e-mail: japansales@powerint.com KOREA Seoul, Korea Phone: +82-2-782-2840 Fax: +82-2-782-4427 e-mail: koreasales@powerint.com SINGAPORE (ASIA PACIFIC HEADQUARTERS) Singapore Phone: +65-6358-2160 Fax: +65-6358-2015 e-mail: singaporesales@powerint.com TAIWAN Taipei, Taiwan, R.O.C. Phone: +886-2-2727-1221 Fax: +886-2-2727-1223 e-mail: taiwansales@powerint.com UK (EUROPE & AFRICA HEADQUARTERS) United Kingdom Phone: +44-1344-462-300 Fax: +44-1344-311-732 e-mail: eurosales@powerint.com www.powerint.com |
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