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FACSIMILE SYSTEM
The diode bridge can also be represented as shown in Fig. 6-29.
6.1.4 Surge prevention circuit
AC
this reason, a large surge current flows when the power is turned ON. A
thermistor is used to prevent surge current from flowing as there is the dan-
ger that elements on circuits may be destroyed when surge current flows.
When the power is turned ON, the thermistor's resistance value is
increased to limit surge current. After this, current flow causes the ther-
mistor to self-heat which, in turn, lowers the resistance value, making it
easier for current to flow.
When the power is turned back ON immediately after it is turned OFF, the
thermistor's temperature has not sufficiently fallen. So, current flows more
easily, causing surge current to flow. For this reason, take care not to turn
the power back ON immediately after turning it OFF.
6–28
Fig. 6-29 Diode Bridge
input is rectified by the diode bridge, and is charged in capacitor C. For
AC input
Fig. 6-30 Surge Prevention Circuit
C
Thermistor
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