Page 190 - Electrical Equipment Handbook _ Troubleshooting and Maintenance

POWER ELECTRONICS, RECTIFIERS, AND PULSE-WIDTH MODULATION INVERTERS

POWER ELECTRONICS, RECTIFIERS, AND INVERTERS 9.17

FIGURE 9.25 The voltages across the capacitor, SCR, and load,
and the current through the load, when switches S and S are closed.
1 2

FIGURE 9.26 The effect of decreasing R on the output voltage
applied to the load in the circuit of Fig. 9.23.

extreme end of the half-cycle. Figure 9.25 illustrates the voltage and current waveforms
for the circuit.
The power to the load can be changed by decreasing R. The capacitor will charge more
quickly at the beginning of each half-cycle, and the SCR will fire soon. Since the SCR will
be on for a longer period in the half-cycle, more power will be supplied to the load (Fig. 9.26).
The resistor R controls the power flow to the load.

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