Motorola MTR2000 T5544 Instruction / Field Service Manual page 281

CLN1223 – 250W DC-Only Power Supply Module
4
FUNCTIONAL THEORY OF OPERATION
The following theory of operation describes the operation of the power supply circuitry at a functional level. The
information is presented to give the service technician a basic understanding of the functions performed by the
module in order to facilitate maintenance and troubleshooting to the module level. Refer to Figure 2 for a block
diagram of the power supply module.
Supply Circuitry
Note
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Input Reverse-Voltage Protection
The Power Supply Module includes protection from input dc voltage with
reverse-polarity.
The power supply is protected from damage and ensures that no reverse
polarity voltages are supplied to the station modules. If a reverse-voltage
is present, the in-line fuse will blow. This fuse is in line with the input
power cable and not part of the station.
Output Over-Current Protection
An over-current condition on the 14.2 Vdc output is limited by an external
in-line fuse or by the external power source. This fuse is in-line with the
input power cable and not part of the station.
The 5.1Vdc regulator is protected by internal current limiting. The trip
point for the 5.1 Vdc output is greater than 115% of the maximum current
specified for the outputs. The 5.1Vdc recovers automatically after the re-
moval of the overload condition.
Over-Voltage Detection and Shutdown
The 5.1 Vdc output is protected from continuous over-voltages by detec-
tion circuits that cause the supply to shutdown and then try to restart it-
self.
68P81096E52-A
09/30/05