
40 Electric Motors and Drives
VOLTAGE CONTROL - D.C OUTPUT FROM D.C.
SUPPLY
For the sake of simplicity we will begin with the problem of
controlling the voltage across a resistive load, fed from a
battery. Three different methods are shown in Figure 2.2. The
battery voltage is assumed to be constant at 12 V, and we
seek to vary the load voltage from 0 to 12 V. Although this is
not quite the same as if the load was a d.c. motor the con-
clusions which we draw are effectively the same.
Method (a) uses a variable resistor (R) to absorb whatever
fraction of the battery voltage is not required at the load. It
provides smooth control, but the sna