IRPLPFC1

Application Note AN-1179 IRPLPFC1 90-265VAC PFC Pre-regulator By Peter B. Green Table of Contents Page 1. Introduction ......................................................................................2 2. Power Factor and THD.....................................................................3 3. PFC Functional Description..............................................................6 4. Design Equations .............................................................................11 5. Factors affecting PF and THD..........................................................14 6. PCB Layout Considerations .............................................................16 7. Bill of Materials.................................................................................19 8. Test Results .....................................................................................21 Safety Warning The IRPLPFC1 power factor correction pre-regulator is based on a non-isolated Boost SMPS circuit topology. The output is nominally 420VDC. When operating the output produces potentially dangerous voltages Additionally short circuiting or overloading the output will damage the board. The IRPLPFC1 demo board should be handled by qualified electrical engineers only AN-1179 www.irf.com 1 EVALUATION BOARD - IRPLPFC1 1. Introduction Many offline applications require power factor correction circuitry in order to minimize transmission line losses and stress on electrical generators and transformers created by high harmonic content and phase shift. Electronic appliances often incorporate switching power supplies (SMPS) which include capacitive filter circuitry followed by a bridge rectifier and bulk capacitor supplying a load. Without power factor correction circuitry a SMPS draws a high peak current close to the line voltage peak and almost no current over much of the cycle, resulting in a power factor of around 0.5 with high total harmonic distortion. Power factor correction circuitry can be added to enable the appliance to draw a sinusoidal current from the AC line with negligible phase shift and very low harmonic distortion. This represents the best type of load for the power transmission grid so that power can be supplied without creating additional conductive losses in transmission lines or additional burden on transformers and generators. Costs to electricity providers are therefore reduced, which passes savings on to the consumer. The trend towards more efficient power utilization for offline appliances, power supplies and lighting converters makes high power factor and low total harmonic distortion of the line input current (THDi) desirable. Standards for power quality exist such as EN61000-3-2 in which specific current harmonic limits are detailed for various different applications. Compliance with class C limits is required for electronic lighting ballasts rated at 25W or above. Market preferences often require LED converters and light fixtures to offer good performance at even lower power ratings. For a product incorporating active power factor correction a THDi of less than 20% over a wide input voltage range, normally 100VAC to 305VAC is expected. In many cases THDi of less than 10% can be achieved over much or all of this voltage range. AN-1179 www.irf.com 2