Design Example Report Title 4.8 W Buck-Boost Converter Using LNK306P Specification Input: 85 - 135 VAC Output: -24 V / 0.2 A Application Home Appliance Author Power Integrations Applications Department Document Number DER-59 Date June 6, 2006 Revision 1.1 Summary and Features • • • • • • • • • • • Non-Isolated Topology - no direct path from input to output Low cost off the shelf inductor – no custom transformer required 15 components including EMI filter Loop Fault Protection Short Circuit Protection Hysteretic Thermal Shutdown Output Referenced to Neutral Precise Output Voltage control Frequency Jitter Excellent Conducted EMI (>10 dB margin across spectrum) Extremely low standby power consumption (<150 mW) 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. Power Integrations 5245 Hellyer Avenue, San Jose, CA 95138 USA. Tel: +1 408 414 9200 Fax: +1 408 414 9201 www.powerint.com DER-59 -24 V / 200 mA LNK306 Buck-Boost Circuit June 6, 2006 Table Of Contents 1 2 3 4 5 6 7 Introduction .................................................................................................................3 Power Supply Specification ........................................................................................4 Schematic ...................................................................................................................5 Circuit Description.......................................................................................................6 PCB Layout.................................................................................................................7 Bill Of Materials...........................................................................................................8 Performance Data.......................................................................................................9 7.1 Efficiency .............................................................................................................9 7.2 Standby Power Consumption ..............................................................................9 7.3 Line/Load Regulation.........................................................................................10 8 Waveforms................................................................................................................11 8.1 Switch Node Voltage and LinkSwitch-TN Drain Current, Normal Operation......11 8.2 Output Voltage Start-up Profile ..........................................................................11 8.3 Load Transient Response (50% to 100% Load Step)........................................12 8.4 Output Ripple Measurements ............................................................................13 8.4.1 Ripple Measurement Technique.................................................................13 8.4.2 Measurement Results.................................................................................14 9 Conducted EMI .........................................................................................................15 10 Revision History ....................................................................................................16 Important Note: Although this board is designed to satisfy safety isolation requirements, the engineering prototype has not been agency approved. Therefore, all testing should be performed using an isolation transformer to provide the AC input to the prototype board. Design Reports contain a power supply design specification, schematic, bill of materials, and transformer documentation. Performance data and typical operation characteristics are included. Typically only a single prototype has been built. Page 2 of 17 Power Integrations Tel: +1 408 414 9200 Fax: +1 408 414 9201 www.powerint.com DER-59 -24 V / 200 mA LNK306 Buck-Boost Circuit June 6, 2006 1 Introduction This document is an engineering report describing a non-isolated buck-boost (inverting) power supply utilizing a LNK306P. This power supply is intended as a power supply for an appliance application. The document contains the power supply specification, schematic, bill-of-materials, printed circuit layout, and performance data. Line -24VDC Neutral RTN Figure 1 – Populated Circuit Board Photograph. Page 3 of 17 Power Integrations Tel: +1 408 414 9200 Fax: +1 408 414 9201 www.powerint.com DER-59 -24 V / 200 mA LNK306 Buck-Boost Circuit June 6, 2006 2 Power Supply Specification Description Input Voltage Frequency No-load Input Power (230 VAC) Output Output Voltage 1 Output Ripple Voltage 1 Output Current 1 Total Output Power Continuous Output Power Efficiency Symbol Min Typ Max Units Comment VIN fLINE 85 47 135 64 0.15 VAC Hz W 2 Wire – no P.E. 50/60 VOUT1 VRIPPLE1 IOUT1 -26.4 -24 -21.6 400 0.2 V mV A 4.8 W % POUT η ± 10% 20 MHz Bandwidth o Measured at POUT (4.8 W), 25 C Environmental Conducted EMI Meets CISPR22B / EN55022B Designed to meet IEC950, UL1950 Class II Safety Surge TBD kV Surge TBD kV Ambient Temperature Page 4 of 17 TAMB 0 70 o C 1.2/50 µs surge, IEC 1000-4-5, Series Impedance: Differential Mode: 2 Ω Common Mode: 12 Ω 100 kHz ring wave, 500 A short circuit current, differential and common mode Free convection, sea level Power Integrations Tel: +1 408 414 9200 Fax: +1 408 414 9201 www.powerint.com DER-59 -24 V / 200 mA LNK306 Buck-Boost Circuit June 6, 2006 3 Schematic R3 20.5k 1% C5 J16 1 47 ohm/2W LINE D1 L1 C4 D2 10uF/16V 1N4004GP D3 BP 1 Fusible 1N4004GP 85-135VAC 60Hz FB + R4 1.54k 1% D 2.2mH + C1 10uF/200V S 1N4936 + C2 10uF/200V L2 1800uH C3 47uF/35V + RF1 0.1uF U1 LNK306P R2 22k J17 1 1 NEUTRAL Figure 2 – Schematic. Page 5 of 17 Power Integrations Tel: +1 408 414 9200 Fax: +1 408 414 9201 www.powerint.com -24V 200mA DER-59 -24 V / 200 mA LNK306 Buck-Boost Circuit June 6, 2006 4 Circuit Description The circuit shown in Figure 2 is a non-isolated buck-boost (inverting) topology. The input voltage range is 85 to 135 VAC 50/60Hz and provides a regulated –24 V at 200 mA. The buck-boost topology is essentially the non-isolated version of the Flyback Converter, in that the transformer is replaced with a single low cost inductor (L2). RF1 is a fusible link resistor. The input AC is half-wave rectified and filtered by D1 and C1. C1, L1 and C2 form a pi-filter network to reduce common-mode emissions imposed to the input line, this in conjunction with the built-in frequency jitter of the LinkSwitch-TN (U1) ensure sufficient conducted EMI margins. U1, D2 and L2 form the buck-boost switching cell, which converts the rectified bulk positive DC voltage on C2 into a negative voltage on C3 (w/r/t Neutral/GND). D2 samples the output voltage onto C4 as a positive voltage with respect to the source of U1. The EN pin of U1 is internally set to 1.63 V (w/r/t pins 1,2, 7 and 8) this in conjunction with resistors R3 and R4 form a simple voltage divider to precisely set the output voltage to the desired level. C5 is a bypass capacitor that serves as high frequency decoupling and energy storage. This capacitor provides power to the IC as well as controls the auto-restart mechanism in the LinkSwitch-TN. Resistor R2 serves to reduce peak charging effects on C3 which tend to increase the output voltage, its static power dissipation is limited to less than 30 mW. Without this additional resistor the standby power consumption would be less than 100 mW. Page 6 of 17 Power Integrations Tel: +1 408 414 9200 Fax: +1 408 414 9201 www.powerint.com DER-59 -24 V / 200 mA LNK306 Buck-Boost Circuit June 6, 2006 5 PCB Layout (RF2 not used) Figure 3 – Printed Circuit Layout. Page 7 of 17 Power Integrations Tel: +1 408 414 9200 Fax: +1 408 414 9201 www.powerint.com DER-59 -24 V / 200 mA LNK306 Buck-Boost Circuit June 6, 2006 6 Bill Of Materials Item Qty Ref Des 1 2 3 4 5 6 7 8 9 10 11 12 13 Page 8 of 17 2 1 1 1 2 1 1 1 1 1 1 1 1 C1, C2 C3 C4 C5 D1, D2 D3 L1 L2 R2 R3 R4 RF1 U1 Value Manufacturer P/N 10uF/250V 47uF/35V 100uF/16V 1uF/50V Standard Rec. 1A/400V Fast Recovery 1A/400V 2.2mH 1800uH 22k 5% 1/4W 20.5k 1% 1/8W 1.54k 1% 1/8W 47 ohm/2W PWM +MOSFET Panasonic ECA-2EM100 Diodes, Inc. Diodes, Inc. Toko Toko 1N4004GP 1N4936 262LY-222K 824MY-182K RCD Components Power Integrations LNK306P Power Integrations Tel: +1 408 414 9200 Fax: +1 408 414 9201 www.powerint.com DER-59 -24 V / 200 mA LNK306 Buck-Boost Circuit June 6, 2006 7 Performance Data All measurements performed at room temperature, 60 Hz input frequency. 7.1 Efficiency 100.00% 90.00% 80.00% Efficiency (%) 70.00% 60.00% Vin = 85VAC 50.00% 40.00% Vin = 120VAC 30.00% 20.00% Vin = 135VAC 10.00% 0.00% 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2 Load Current (ADC) Figure 4 – Efficiency vs. Input Voltage. 7.2 Standby Power Consumption Input Power (W) 0.15 0.125 0.1 0.075 0.05 90 120 135 Input AC Voltage (VAC) Figure 5 – Standby Power Consumption vs. Input Voltage. Page 9 of 17 Power Integrations Tel: +1 408 414 9200 Fax: +1 408 414 9201 www.powerint.com DER-59 7.3 -24 V / 200 mA LNK306 Buck-Boost Circuit June 6, 2006 Line/Load Regulation 125.00% No Load 120.00% Light Load (50mA) Output Voltage Regulation (%) 115.00% 110.00% Half Load (100mA) 105.00% Full Load (200mA) 100.00% 95.00% 90.00% 85.00% 80.00% 75.00% 80 90 100 110 120 130 140 Input Voltage (VAC) Figure 6 – Line/Load Regulation, Room Temperature. Page 10 of 17 Power Integrations Tel: +1 408 414 9200 Fax: +1 408 414 9201 www.powerint.com DER-59 -24 V / 200 mA LNK306 Buck-Boost Circuit June 6, 2006 8 Waveforms 8.1 Switch Node Voltage and LinkSwitch-TN Drain Current, Normal Operation Figure 7 – 85VAC, Full Load. Upper: IDRAIN, 0.2 A / div Lower: VSwitch-Node, 50 V, 2 µs / div 8.2 Figure 8 – 135VAC, Full Load Upper: IDRAIN, 0.2 A / div Lower: VSwitch-Node, 50 V / div Output Voltage Start-up Profile Figure 9 – Start-up Profile, 120VAC (No Load) 5 V, 10 ms / div. Page 11 of 17 Figure 10 – Start-up Profile, 120 VAC (Full Load) 5 V, 50 ms / div. Power Integrations Tel: +1 408 414 9200 Fax: +1 408 414 9201 www.powerint.com DER-59 -24 V / 200 mA LNK306 Buck-Boost Circuit June 6, 2006 8.3 Load Transient Response (50% to 100% Load Step) In the figures shown below, signal averaging was used to better enable viewing the load transient response. The oscilloscope was triggered using the load current step as a trigger source. Since the output switching and line frequency occur essentially at random with respect to the load transient, contributions to the output ripple from these sources will average out, leaving the contribution only from the load step response. Figure 11 – Transient Response, 120 VAC, 50-100-50% Load Step. Top: Load Current, 0.2 A/div. Bottom: Output Voltage 2V (24V Offset), 2ms / div. Page 12 of 17 Power Integrations Tel: +1 408 414 9200 Fax: +1 408 414 9201 www.powerint.com DER-59 8.4 -24 V / 200 mA LNK306 Buck-Boost Circuit June 6, 2006 Output Ripple Measurements 8.4.1 Ripple Measurement Technique For DC output ripple measurements, a modified oscilloscope test probe must be utilized in order to reduce spurious signals due to pickup. Details of the probe modification are provided in Figure 12 and Figure 13. The 5125BA probe adapter is affixed with two capacitors tied in parallel across the probe tip. The capacitors include one (1) 0.1 µF/50 V ceramic type and one (1) 1.0 µF/50 V aluminum electrolytic. The aluminum electrolytic type capacitor is polarized, so proper polarity across DC outputs must be maintained (see below). Probe Ground Probe Tip Figure 12 – Oscilloscope Probe Prepared for Ripple Measurement. (End Cap and Ground Lead Removed) Figure 13 – Oscilloscope Probe with Probe Master 5125BA BNC Adapter. (Modified with wires for probe ground for ripple measurement, and two parallel decoupling capacitors added) Page 13 of 17 Power Integrations Tel: +1 408 414 9200 Fax: +1 408 414 9201 www.powerint.com DER-59 -24 V / 200 mA LNK306 Buck-Boost Circuit June 6, 2006 8.4.2 Measurement Results Figure 14 – Ripple, 85VAC, Full Load. 2 ms, 200 mV / div Page 14 of 17 Figure 15 – Ripple, 135VAC, Full Load. 2 ms, 200 mV / div Power Integrations Tel: +1 408 414 9200 Fax: +1 408 414 9201 www.powerint.com DER-59 9 -24 V / 200 mA LNK306 Buck-Boost Circuit June 6, 2006 Conducted EMI Figure 16 – Conducted EMI EN55022 B Limits - 120 VAC/60Hz Maximum Steady State Load (LINE) Note: If more EMI margin is desired, an additional 1N4007 can be added in series with the NEUTRAL input . Figure 17 – Conducted EMI EN55022 B Limits - 120 VAC/60Hz Maximum Steady State Load (Neutral) Page 15 of 17 Power Integrations Tel: +1 408 414 9200 Fax: +1 408 414 9201 www.powerint.com DER-59 -24 V / 200 mA LNK306 Buck-Boost Circuit June 6, 2006 10 Revision History Date May 4, 2005 June 6, 2006 Page 16 of 17 Author RSP PV/SF Revision 1.0 1.1 Description & changes Initial Release Updated tolerance in Section 2 from 5% to 10%. Adjusted output voltages accordingly. Reviewed VC / AM KM Power Integrations Tel: +1 408 414 9200 Fax: +1 408 414 9201 www.powerint.com DER-59 -24 V / 200 mA LNK306 Buck-Boost Circuit June 6, 2006 For the latest updates, visit our website: 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. PATENT INFORMATION 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, DPA-Switch and EcoSmart are registered trademarks of Power Integrations. PI Expert and PI FACTS are trademarks of Power Integrations. © Copyright 2005 Power Integrations. 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