Vicor DC-DC Converter Theory DC-DC Converter Power Train LD D1 + Vin C RES LOAD D2 SW 1 I1 CTRL Simplified ZCS cell I2 Maxi, Mini, Micro block diagram Common Drain FET Reverse Boost FET Transformer Coupling Topology: ZCS Power Transfer Q1 ON OFF IQ1 t I V/LD t VCres V I/Cres t D1 ON OFF t t1 t2 t3 t4 A ZCS quasi-resonant converter regulates the output voltage by varying its switching frequency. The LC resonant frequency is fixed so the “on” time of the switch is approximately 400 to 500ns. I I T1 On time of the switching T2 Pulse repetition rate/operating frequency T3 Rise and fall time of the current in the switching device PWM Variable Fixed Fixed ZCS Fixed Variable Fixed Basic requirements for DC-DC converters An input fuse (for fire protection). An input capacitor (to restore low source impedance). Common-mode by-pass capacitors to improve EMI and transient immunity. Sense connections must be made. Baseplate earthed. Thermal and mechanical considerations Electrical Performance Thermal Considerations Power Input = Power Dissipated as Heat + Power Output Power Dissipated = (1 - h)/h x Power Output Power Input x Efficiency (h) = Power Output Heat is removed through the flat metal baseplate on top of the module The baseplate is thermally coupled to, but electrically isolated from heat generating components Methods of cooling: Conduction Convection Radiation Efficiency Performance of a Typical V48C12C150B Electrical Performance Thermal considerations Heat sinks Transverse fins Longitudinal fins How to get the lowest noise For thermal reasons the power semi-conductors are mounted onto a metal surface. An insulating layer (Kapton or ceramic tab) guarantees galvanic insulation. The MOSFET and the diodes are coupled through parasitic capacitance. Primary Base plate CRectifier CFET AC VP ICM VP Secondary ICM On each switching cycle of the MOSFET an impulsive current (the common mode current) flows through the parasitic capacitors. This current flows on the protective earth connection and disturbs other systems on the same AC net. Primary Base plate CFET Secondary CRectifier IDM AC VP Cexternal Cexternal Y caps External decoupling capacitors and common mode chokes reduce the effects of the common mode current. EMI Compliance Common mode filter C1: 120µF 100V electrolytic capacitor C2, C3: 4.7nF ‘Y’ capacitors C4: 2.2µF polyester capacitor L: 2x 0.42mH Vicor P/N 36-00037 common mode inductor EMI Compliance Common mode filter 50% FL 100% FL V48C48C150AL EMI Compliance Implementation effect of bypass capacitors Bypass capacitors next to the module 100% FL Bypass capacitors far from the module V48C48C150AL