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Figure 14 illustrates a typical SCR regulated supply whose output is continuously variable down to near zero
volts. Circuit operation is very similar to the SCR preregulators described previously, except that the SCR
control circuit receives its input from the voltage comparison amplifier. The control circuit computes the firing
time for the SCRs, varying this in a manner which will result in a constant output despite changes in line
voltage or load resistance. The control circuit is capable of making a nearly complete correction within the first
half-cycle (8.3msec) following a disturbance.
Figure 14. SCR Regulated Power Supply
CONSTANT CURRENT POWER SUPPLY
The ideal constant current power supply exhibits an infinite output impedance (zero output admittance) at all
frequencies. Thus, as Figure 15 indicates, the ideal constant current power supply would accommodate a load
resistance change by altering its output voltage by just the amount necessary to maintain its output current at a
constant value.
Constant current power supplies find many applications in semiconductor testing and circuit design, and are
also well suited for supplying fixed currents to focus coils or other magnetic circuits, where the current must
remain constant despite temperature-induced changes in the load resistance. Just as loads for constant voltage
power supplies are always connected in parallel (never in series), loads for constant current power supplies
must always be connected in series (never in parallel).