This is done by creating a voltage divider of a resistive element in the regulator and the resistance of the
load. Regulation is achieved by varying the resistance of the resistive element in the regulator.
A SERIES REGULATOR uses a variable resistance in series with the load. Regulation is achieved
by varying this resistance either to increase or to decrease the voltage drop across the resistive element of
the regulator. Characteristically, the resistance of the variable resistance moves in the same direction as
the load. When the resistance of the load increases, the variable resistance of the regulator increases;
when load resistance decreases, the variable resistance of the regulator decreases.
SHUNT REGULATORS use a variable resistance placed in parallel with the load. Regulation is
achieved by keeping the resistance of the load constant. Characteristically the resistance of the shunt
moves in the opposite direction of the resistance of the load.
The CURRENT LIMITER is a short-circuit protection device that automatically limits the current
to a safe value. This is done when the current-limiting transistor senses an increase in load current. At this
time the current-limiting transistor decreases the voltage on the base of the pass transistor in the regulator,
causing a decrease in its conduction. Therefore, current cannot rise above a safe value.
TROUBLESHOOTING is a method of detecting and repairing problems in electronic equipment.
Two methods commonly used are the VISUAL CHECK and SIGNAL TRACING. The visual check
allows the technician to make a quick check of component problems, such as shorts, discolored or leaky
transformers, loose or broken connections, damaged resistors or capacitors, smoking parts, or sparking.
The signal tracing method is used when the technician cannot readily see the problem and needs to use
test equipment. Component failure is also important in troubleshooting. In transformers and chokes, a
winding can open, or two or more windings can short, either to themselves or to the case that is usually
grounded. In a capacitor only two things can occur: either it can short and act as a resistor, or it can open,
removing it from the circuit. A resistor can open, increase in value, or decrease in value.
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