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Chapter 17

Control Devices

One of the most efficient methods of electrical power control that is
circuit switching. When a switch is turned on, power is consumed by the
load device. When a switch in any circuit is turned off, no power is con-
sumed. This switching method of power control is shown in Figure 17-1
using a lamp as the load device. Since the switch is low resistant, it con-
sumes little power. When the switch is open, it consumes no power. By
switching the circuit on and off rapidly, the average current flow can be
reduced. The brightness of the lamp will also be reduced. In effect, lamp
brightness is controlled by the switching speed. Power in this method of
control is not consumed by the control device. This type of power control
is both efficient and effective.
The switching method of electrical power control cannot be achieved
effectively with a manual switch. The mechanical action of the switch will
not permit it to be turned on and off quickly. A switch would soon wear
out if used in this manner. Electronic switching can be used to achieve the
same result. Switching action of this type can be accomplished in a circuit
without a noticeable flicker of a lamp. Electronic control devices such as
silicon controlled rectifiers and triacs are used with the switching method
for controlling power. The operation of these devices is described in this
chapter.

Figure 17-1. Switch-controlled lamp circuit.