Lambda EMS 7.5-75 Operator's Manual

Contents

Lambda EMS 7.5-75 Operator's Manual Manual pdf 32 page image

4 THEORY OF OPERATION4.1 PRINCIPLES OF OPERATIONThe basic principle of operation is outlined in this section. A simplified diagram of theEMS power supply is shown below in figure 4.1. The power supply is made of the inputsection ( rectifier and the filter), the inverter (A200 Bd.), the output section, and the controlsection which is made of the A100 Bd. The input AC voltage is rectified and filtered toproduce an unregulated high voltage dc. The unregulated high voltage dc is then convertedby the inverter (A200 Bd.) into a high frequency ac square wave. This waveform is steppedup or down by a high frequency isolation transformer. The secondary output is rectified andfiltered to produce the required low ripple output voltage. The output is attenuated down andcompared against a reference voltage, thus regulating the output. Regulation is achievedthrough modulation of the pulse-width generated by the control stage (A100 Bd.).Figure 4.1: Simplified EMS Power Supply4.2 INPUT SECTIONThe AC input enters through TB2 on the rear of the unit. It passes through the power linefilter on the A300 board. The purpose of the Power Line Filter is to attenuate high frequencyconducted emissions generated inside the unit, thus reducing the high frequency currentemitted onto the power source. The load side of the line filter connects to a DPDT switchwhich allows power to pass through to the rectifier bridge to supply the DC bus capacitorsC1 and C2. At turn on, the contact of K1 is in the open position, limiting the inrush currentthrough the rectifiers. After a delay of about 3 to 4 seconds, the contact closes allowingnormal power transfer. The input AC voltage is rectified and filtered producing anunregulated high voltage dc.4.3 A200 INVERTER BOARDThe unregulated high voltage DC is fed into the A200 Inverter board, which consists of a setof power transistors configured as a half or full bridge inverter (half bridge for the600W/1KW). The DC bus is locally bypassed by two capacitors minimizing the area of high83-473-000 Revision J4 - 1 Theory of Operation