TC 9-62
Figure 4-48. Voltage Tripler
Figure 4-49. Full-wave Voltage Doubler
SHORT CIRCUIT PROTECTION
4-131. 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
can 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. Figure 4-50 shows a series regulator with a current-limiting circuit. You should
remember that in order for a silicon NPN transistor to conduct, the base must be between
0.6 volts to 0.7 volts more positive than the emitter. Resistor R4 will develop a voltage
drop of 0.6 volts when the load current reaches 600 milliamperes. This is shown by using
Ohm's law:
E 0.6volt
=
= .6 amphere or 600 milliamperes
I=
R 1 ohm
4-42
TC 9-62
23 June 2005
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