® Design Idea DI-18 LinkSwitch Low Cost 2.75 W CV/CC Charger or Adapter Application Device Power Output Input Voltage Output Voltage Topology Charger/Adapter LNK501 2.75 W 85-265 VAC 5.5 V Flyback Design Highlights • Replaces a linear transformer based supply at the same or lower cost but with much higher performance • <0.3 W consumption at zero load meets worldwide guidelines (EC’s 0.3 W, USA’s 1 W for example) • Extremely simple circuit – only 17 components (14 with integrated bridge) for production-worthy design • Primary based CV/CC output – no secondary sense components required • ±10% output voltage and ±20% output current tolerances at peak power point • Fully protected for thermal, short circuit and open loop faults • >70% efficiency • Meets CISPR22B/EN55022B and FCC B EMI limits • Meets 2.5 kV EN61000-4-5 differential surge • Ultra-low leakage current design <5 µA • EE13 core for low cost and small size Operation The AC input is rectified and filtered by D1-D4, C1 and C2. Conducted EMI filtering is provided both by a π filter (C1, L1 and C2) and a differential filter (RF1 and C1). Together with a shield in the transformer (formed from part of the primary) the design meets conducted EMI limits with no Y-capacitor between primary and secondary. Resistor RF1 also functions as a fuse. D1, D2, D3, D4 1N4005 X 4 L1 1 mH LinkSwitch D 85 - 265 VAC C1 4.7 µF 400 V C2 4.7 µF 400 V Together with D5, C4 and R1 are also part of the primary clamp, limiting the peak drain to source voltage due to leakage inductance. Resistor R2 filters the leading edge leakage inductance spike, reducing the error in the feedback voltage. The CONTROL pin capacitor C3 provides energy storage for supply startup and sets auto-restart timing during fault conditions. Key Design Points • Select transformer turns ratio to give a VOR of 40-60 V. Lower values reduce power capability, higher values increase no-load consumption. • R1 provides 2.3 mA into the CONTROL pin at the peak power point at 85 VAC. The value can be adjusted to center the output voltage. T1 S C RF1 10 Ω 1 W Fusible LinkSwitch derives all feedback information from the primary. During output diode conduction, the output voltage transformed through the turns ratio is sampled and held by C4. The feedback voltage across C4 (VOR) is converted into feedback current by R1 and fed into the CONTROL pin. This feedback current regulates the output by PWM control during CV operation, and by reducing the internal current limit during CC operation. Below an output voltage of ~2 V LinkSwitch enters auto-restart, limiting average output current to <50 mA. The nominal transition from CV to CC occurs at 5.5 V, 0.5 A. The output envelope characteristic and specification limits are shown in Figure 2. U1 LNK501 R1 20.5 kΩ 1% C3 0.22 µF 50 V C4 0.1 µF 100 V 1 104 T 34 AWG 4 5.5 V, 0.5 A 5 15 T 30 AWG T.I.W. 6 12 T 2 x 30 AWG 3 EE13 LP=2.55 mH C5 470 µF 10 V RTN D6 11DQ06 1A, 60 V D5 1N4937 R2 100 Ω PI-3364-091602 Figure 1. LinkSwitch 2.75 W Charger Power Supply: 85 VAC to 265 VAC Input, 5.5 V, 0.5 A Output DI-18 www.powerint.com September 2002 DI-18 VIN=115 V VIN=185 V VIN=265 V 8 6 4 2 0 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 TDK PC40 EE13, ALG=190 nH/T2 Core Bobbin EE13 Horizontal 8 pin Primary: 104T, 34 AWG Shield: 12 T, 2 x 30 AWG Secondary: 15T, 30 AWG T.I.W. Flux Band: 1T, 6 mm Cu foil (T.I.W.: Triple Insulated Wire) Secondary (5-6), tape, Shield (3-4), tape, Primary (4-1), tape, Flux band (3-NC) Winding Details Winding Order (pin numbers) Inductance Primary: 2.55 mH ±10%, Leakage: 50 µH (max.) Primary Resonant Frequency 300 kHz (minimum) Table 1. Transformer Construction Information. 0.3 PI-3362-091602 VIN=85 V TRANSFORMER PARAMETERS No-Load Power Consumption (W) Output Voltage (V) 10 PI-3363-091402 • To maintain the ±20% CC tolerance the primary inductance tolerance should be tighter than ±10%. • Minimize zero load consumption by reducing drain node capacitance: Use double coated/grade 2 wire for primary and do not vacuum impregnate. Avoid using an RC snubber across the output diode. • For resistive loads increase C3 to 1 µF (electrolytic) to allow adequate time for start-up at full load. • For battery loads an output π filter is typically not required but can be added for resistive loads to reduce switching ripple. • L1 can be replaced with a 22 Ω to 100 Ω fusible resistor for lower cost but lower efficiency (~10% reduction). • Adding a 1 mA to 2 mA pre-load reduces zero load voltage by ~1V but increases power consumption by ~10 mW. • Diode D6 can be replaced with a PN diode for lower cost but reduced efficiency. • See AN-35 and EPR-16 for more information. 0.25 0.2 0.15 0.1 85 VAC: 174 mW 115 VAC: 179 mW 185 VAC: 211 mW 230 VAC: 229 mW 265 VAC: 250 mW 0.05 Output Current (A) 0 50 100 150 200 250 300 Input Voltage (VAC) Figure 2. Load Regulation - CV/CC Characteristics with Limits. Figure 3. No-load Input Power Consumption. 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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