Motorola MTR2000 T5544 Instruction / Field Service Manual page 276

CLN1222 – 500W 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 28.6 Vdc output is limited by an external
in-line fuse or the external power supply. This fuse is in-line with the input
power cable and not part of the station.
The trip point for the 14.2 Vdc and 5.1 Vdc outputs is greater than 115% of
the maximum current specified for the outputs. The power supply recov-
ers automatically after the removal of the overload condition.
Over-Voltage Detection and Shutdown
The 14.2 Vdc and 5.1 Vdc outputs are protected from continuous over-
voltages by detection circuits that cause the supply to shutdown and then
try to restart itself.
Also, the 14.2 Vdc output is protected by a crowbar circuit if failure of any
part causes the 28.6 Vdc output to connect directly to the 14.2 Vdc output.
The trip point of the over-voltage detection circuit is less than 16.8 Vdc for
14.2 Vdc, and less than 6.0 Vdc for 5.1 Vdc.
68P81096E51-A
09/30/05