® Design Idea DI-22 ® TOPSwitch-GX 70 W, 19 V External Laptop Adapter Application Device Power Output Input Voltage Output Voltage Topology Laptop Adapter TOP249Y 70 W 85-265 VAC 19 V Flyback Design Highlights Operation • High efficiency: 84% at 85 VAC (with 50 ˚C external ambient temperature) • Low component count and high power density, 7 W/in.3 • Very compact design (4.1 in. × 2.225 in. × 1.06 in.) • No surface mount components required • Low zero load power consumption, <370 mW at 115 VAC • Approximately constant overload power with line voltage • Line undervoltage detection (UV) and overvoltage (OV) shutdown • Low EMI - switching frequency jitter helps meet CISPR22B/ EN55022B limits • Fully protected for overload, short circuit and thermal faults The design utilizes a TOP249Y in a flyback converter providing a 70 W output in a sealed enclosure at an external ambient of 50 ˚C. Line UV and OV (100 V and 450 V, respectively) are implemented using a single 2 MΩ resistor (R1). Undervoltage eliminates power-up/down glitches and overvoltage provides line transient and long duration power system surge protection. Resistor R10 programs the internal current limit to 75% of nominal at the UV threshold. As a function of input voltage the current limit is further reduced by R9 to provide approximately constant overload power. The larger TOPSwitch-GX selection reduces conduction losses, raising efficiency (without circuit changes or increased overload power) and permits a higher inductance design for reduced primary RMS currents, further increasing efficiency. C7 2.2 nF C13 C12 C11 0.33 µF 0.022 µF 0.01 µF 400 V 400 V 400 V D2 MBR20100 Y1 Safety BR1 RS805 8 A 600 V 1 2 VR1 P6KE200 2 9 D1 UF4006 C6 0.1 µF X2 RT1 10 Ω 1.7 A F1 3.15 A t° L3 75 µH 2A 6 S C2 820 µF 25 V 5 R2 1 kΩ C15 L X C TOP249Y U1 F C8 0.1 µF 50 V R10 20.5 kΩ 85-265 VAC 19 V, 3.6 A C4 820 µF 25 V R4 31.6 kΩ 1% R1 270 Ω U2 PC817A R8 4.7 Ω R13 562 Ω C9 1% 4.7 nF 50 V TOPSwitch-GX 1 µF CONTROL R9 13 MΩ C14 0.1 µF 50 V RTN D4 1N4148 T1 D L1 200 µH 8 R11 2 MΩ 1/2 W C1 150 µF 400 V C3 820 µF 25 V 11 3 L2 820 µH 2A D3 MBR20100 50 V R3 6.8 Ω C5 47 µF 16 V U3 TL431 R7 56 kΩ C10 0.1 µF 50 V R6 4.75 kΩ 1% PI-2691-033001 Figure 1. TOPSwitch-GX 70 W Laptop Adapter Schematic. DI-22 www.powerint.com September 2002 DI-22 To reduce winding and diode dissipation the secondary is split into two windings and diode OR’ed into the output capacitors (C2, 3). Regulation is provided by a secondary side reference (U3), the output voltage sensed by R4, R13 and R6. TRANSFORMER PARAMETERS Core Material FPQ26/20-A 2 TDK PC40 gappped for ALG = 843 nH/T Bobbin TDK BPQ26/20-1112CP Winding Details Primary: 9T + 9T, 2 x 26 AWG Shield: 1T, 8 mm x 0.015 mm Cu foil Secondary 1: 3T, 3 x 26 AWG T.I.W. Secondary 2: 3T, 3 x 26 AWG T.I.W. Bias: 2T, 8 mm x 0.015 mm Cu foil (T.I.W. = Triple Insulated Wire) Winding Order (Pin Numbers) Primary (2-1), Shield (1-NC), tape, Secondary 1 (12-9), Secondary 2 (11-8), Bias (6-5), tape, Primary (3-2), tape Inductance Primary: 273 µH ± 10%, Leakge: 3 µH (maximum) Primary Resonant Frequency 1.5 MHz (minimum) Key Design Points • D1 and VR1 clamp leakage inductance spikes. A Zener clamp provides lower zero load consumption than an RCD clamp and higher efficiency below full load. • C11 reduces VR1 dissipation, raising efficiency. • Additional differential filtering is provided by C13 and L3. • C12 provides high frequency bypass, reducing high frequency EMI. • Use foil windings to reduce dissipation and reduce leakage inductance. • Sandwich secondary winding between two halves of primary to reduce leakage inductance. • High core temperature reduces saturation flux density. Keep flux density below 3000 gauss (0.3 T) to prevent saturation. • Use 100 V Schottky diodes for highest efficiency. • Good layout practices should be followed: - Locate C8, R3, C5, R9, R10 and R11 close to U1. - Power and signal source currents should be separated, joined using a Kelvin connection at the SOURCE pin. - Minimize the primary and secondary loop areas to reduce parasitic leakage and EMI. • Consult DAK-11 and EPR-11 for more information. Table 1. Transformer Construction Information. 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 and EcoSmart are registered trademarks of Power Integrations, Inc. PI Expert is a trademark of Power Integrations, Inc. ©Copyright 2002, Power Integrations, Inc. WORLD HEADQUARTERS AMERICAS Power Integrations, Inc. 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