4-51
Figure 4-49.—Full-wave voltage doubler.
Q38.
A half-wave voltage doubler is made up of how many half-wave rectifiers?
Q39.
If a half-wave rectifier is added to a half-wave voltage doubler, the resulting circuit is a voltage
____.
Q40.
In a full-wave voltage doubler, are the capacitors connected in series or in parallel with the
output load?
Short Circuit Protection
The main disadvantage of a series regulator is that the pass transistor is in series with the load. If a
short develops in the load, a large amount of current will flow in the regulator circuit. The pass transistor
can be damaged by this excessive current flow. You could place a fuse in the circuit, but in many cases,
the transistor will be damaged before the fuse blows. The best way to protect this circuit is to limit the
current automatically to a safe value. A series regulator with a current-limiting circuit is shown in figure
4-50. You should recall that in order for a silicon NPN transistor to conduct, the base must be between 0.6
volt to 0.7 volt more positive than the emitter. Resistor R4 will develop a voltage drop of 0.6 volt when
the load current reaches 600 milliamperes. This is illustrated using Ohm's law:
