Reference Design Report for a 1.2 W Non- Isolated, Dual Output Buck / Buck-Derived Title Power Supply with Configurable Positive or Negative Outputs Using LNK304DN 85 265 VAC Input, 12 V, 80 mA and 5 V, 50 mA Specification Outputs Application Meters Author Power Integrations Applications Department Document RDR-138 Number Date November 12, 2007 Revision 1.0 Summary and Features Compact, lightweight, low cost, low component count design provides two outputs Outputs configurable as both positive or one positive and one negative Very good cross regulation Integrated safety and reliability features Accurate, auto-recovering, thermal shutdown function maintains safe PCB temperatures under all conditions Auto-restart protects against output short circuits and lost regulation faults Meets CISPR-22/EN55022B limits for conducted EMI with >10 dB margin 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 RDR-138 1.2 W Non Isolated Dual Output Supply 12-Nov-2007 Table of Contents 1 Introduction.................................................................................................................3 2 Power Supply Specification ........................................................................................4 3 Schematic...................................................................................................................5 4 Circuit Description ......................................................................................................6 4.1 AC Input Rectification and EMI Filtering..............................................................6 4.2 LinkSwitch-TN Device .........................................................................................6 4.3 Output Rectification and Filtering ........................................................................7 4.4 Feedback Network ..............................................................................................7 4.5 Linear Regulator..................................................................................................8 5 PCB Layout ................................................................................................................9 6 Bill of Materials .........................................................................................................10 7 Performance Data ....................................................................................................11 7.1 Efficiency...........................................................................................................11 7.1.1 Active Mode CEC Measurement Data........................................................11 7.2 No-load Input Power..........................................................................................13 7.3 Regulation .........................................................................................................13 7.3.1 Load and Line ............................................................................................13 7.3.2 Line ............................................................................................................15 8 Thermal Performance...............................................................................................16 9 Waveforms ...............................................................................................................17 9.1 Drain Voltage and Current, Normal Operation...................................................17 9.2 Output Voltage Start-up Profile..........................................................................17 9.3 Source Voltage and Drain Current Start-up Profile............................................18 9.4 Load Transient Response (75% to 100% Load Step) .......................................19 9.5 Output Ripple Measurements............................................................................21 9.5.1 Ripple Measurement Technique ................................................................21 9.5.2 Measurement Results ................................................................................22 10 Conducted EMI .....................................................................................................23 11 Line Surge.............................................................................................................24 12 Revision History....................................................................................................25 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. Power Integrations Tel: +1 408 414 9200 Fax: +1 408 414 9201 www.powerint.com Page 2 of 28