Design Idea DI-35 ® TOPSwitch-GX 16 W Audio Amplifier Power Supply Application Device Power Output Input Voltage Output Voltage Topology Audio Amplifier TOP245P 16 W (35 W Peak) 85-265 VAC 16 V Flyback The EMI filter has been significantly simplified to three components (L1, CX1 and CY1), thanks to the built-in frequency jitter function of the TOPSwitch-GX family. Design Highlights • • • • • No heatsinks required! 77% efficiency (min), @ 85 VAC input/35 W output Low no-load input power: < 0.7 W @ 230 VAC input Low component count: 37, excluding I/O connectors Stable operation with or without 10,000 µF output buffer capacitor • Robust transformer design enables 35 W peak power • Meets CISPR22B EMI with > 10 dB of margin • Ideal for both class AB and class D audio amplifiers The RCD network of C4, R3, R4, and D5 limits (clamps) the peak voltage that the U1-DRAIN sees. A glass-passivated normal recovery diode (D5) recycles stored leakage energy, increasing overall efficiency. DRAIN ringing is dampened by R4 (which is necessary when a normal recovery diode is used). The bias winding provides operating power and feedback current to the CONTROL pin of U1. The U2-LED, R8 and VR1 comprise the feedback circuit that senses the output voltage. The current through the U2-LED regulates the output voltage, by modulating the feedback current that flows into the CONTROL pin of U1. Operation Many of the built-in TOPSwitch-GX features have been used to reduce the component count, transformer size, and overall cost of this universal input flyback power supply. Designed around a TOP245P (DIP-8 package), the device uses PCB copper for its heatsink, eliminating the costs of both a heatsink and the installation labor. Output diode D7 is also cooled the same way. Key Design Points • Ensure that the control loop has enough phase margin at the extremes of the rated input voltage and output load, both with and without the output buffer capacitor. • A 5% VR1 should be acceptable for an audio amplifier. Greater accuracy will require a 2% VR1. • OV and UV thresholds are determined by: VOV = 225 µA x (R1+R2) and VUV = 50 µA x (R1+R2). Resistors R1 and R2 set the nominal Under-Voltage (UV) lockout and Overvoltage (OV) shutdown limits to 84 V and 378 V, respectively. UV lockout protects the supply from overheating at low line and eliminates power-up and powerdown glitches. OV shutdown protects the power supply from line surges. R3 200 k 1/2 W D1 & D2 1N4007 R1 1M C1 100 µF 400 V D CX1 220 nF 250 VAC F1 3.15 A 250 V R4 33 Ω 1/4 W D5 IN4007G M R6 C6 33 Ω 470 pF 1/4 W 100 V L2 3.3 uH 9, 10 R7 10 Ω 5 T1 C7 C8 470 µF 470 µF 25 V 25 V R8 C5 150 Ω 1 µF 50 V D6 BAV20 TOPSwitch-GX U1 TOP245P 16 V, 1 A / 2.2 A RTN U2 PC817A U2 U2 R10 1k CONTROL C S C2 100 nF 50 V R5 3.3 Ω C3 100 µF 16 V VR1 IN5244B 5% C10 47 µF 25 V N Figure 1. Audio Amplifier Power Supply. DI-35 C9 100 µF 25 V D7 SB5100 6, 7 4 85-265 VAC L 1 3 R2 1M D3 & D4 1N4007 L1 6.8 mH 0.8 A C4 1 nF 1 KV CY1 2.2 nF (Safety) www.powerint.com PI-3731-012604 March 2004 DI-35 • Keep power loop layouts (primary and secondary) tight to minimize noise (EMI and output ripple) and power loss. • At least 10 cm2 of PCB copper area should be used for heatsinking. 16 15.9 Nippon Ceramic EF-25-NC-2H ALG of 247 nH/T2 Core PI-3719-093003 16.1 TRANSFORMER PARAMETERS 15.8 Bobbin Miles-Platts FE0100 with TBS-601 terminals Winding Details Primary: 65T, 2 layers, 28 AWG Secondary: 9T, 2 x 26 AWG, Triple Insulated Bias: 8T, 2 x 28 AWG Primary: 3-1, tape Winding Order (pin numbers) Secondary: 9,10-6,7, tape, Bias: 4-5, tape 3L VOUT (V) 15.7 15.6 15.5 Primary Inductance 15.4 1059 µH ± 10% Primary Resonant Frequency 0.75 MHz (Min) 15.3 Leakage Inductance 15.2 15.1 28 µH (Max) Table 1. Transformer Construction Information. 15 0 0.5 1 1.5 2 2.5 IOUT (A) THERMAL TEST RESULSTS Figure 2. 115 VAC V-I Curve. PI-3730-012604 7 6 5 Current (A) Thermal test load current is 1 A for 30 ms, 2.2 A for 10 ms T (°C) @ T (°C) @ Test Case 85 VAC 265 VAC 4 3 T1 (Transformer) 57 59 U1 (TOP245P 64 51 D7 (Op Rectifier) 58 59 C8 (Op Capacitor) 41 40 Table 2. Thermal Test with Pulsed Load of Figure 3. 25 °C Ambiant, Open Frame, 85 VAC and 265 VAC input. 2 1 0 1A 2.2 A -1 50 0 100 Time (ms) Figure 3. Load Current for Thermal Test. (10 ms/div) For the latest updates, visit www.powerint.com Power Integrations may make changes to its products at any time. Power Integrations has no liability arising from your use of any information, device or circuit described herein nor does it convey any license under its patent rights or the rights of others. POWER INTEGRATIONS MAKES NO WARRANTIES HEREIN AND SPECIFICALLY DISCLAIMS ALL WARRANTIES INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE, AND NON-INFRINGEMENT OF THIRD PARTY RIGHTS. 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. PI Expert and DPA-Switch are trademarks of Power Integrations. Copyright 2004, Power Integrations Power Integrations MAIN PHONE NUMBER +1 408-414-9200 A 3/04 5245 Hellyer Avenue APPLICATIONS HOTLINE +1 408-414-9660 APPLICATIONS FAX +1 408-414-9760 www.powerint.com San Jose, California 95138 For a complete listing of worldwide sales offices, please visit www.powerint.com