Motorola MTR2000 T5544 Instruction / Field Service Manual page 264

CLN1221 – 250W 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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Output Over-Current Protection
An over-current condition on the 14.2 Vdc output causes the total supply
to shutdown and try to restart. If the over-current continues to exist, the
power supply will 'hiccup' until the overload condition is removed, and
will not be damaged by the overload. The 14.2 Vdc output goes into the
hiccup mode when its output current is greater than 18 A. The trip point
for the 5.1 Vdc output is greater than 115% of the maximum current spec-
ified for the output. The power supply recovers automatically after the re-
moval of the overload condition.
Over-Voltage Detection and Shutdown
The 14.2 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. If the over-voltage condition continues to occur, the supply goes into
a 'hiccup' mode of shutting down and trying to restart. If the over-voltage
condition is removed, the supply automatically recovers. In addition, the
5.1 Vdc output is protected by an over-voltage detect circuit that shuts
down both series regulators at the same time. 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.
AC Fail Detect
An AC Fail detect signal is provided to indicate (when used with battery
backup option) that the power supply is operating from an external dc
source rather than the ac mains. This signal is an open collector output ca-
pable of sinking 1mA, and is routed to the Station Control Module. The
active low state indicates ac operation. For the nominal 120 V ac opera-
tion, the signal is active-high impedance (indicating an ac mains failure)
when the ac voltage is less than 85 Vrms, but more than the minimum volt-
age that guarantees that all outputs will be in regulation at full load. For
the nominal 240 Vac operation, the detect point is less than 170 Vrms but
more than the minimum ac input voltage that guarantees that all outputs
be in regulation at full load.
68P81096E34-C
09/30/05