Motorola MTR2000 T5544 Instruction / Field Service Manual page 257

DLN6622 – 500W 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
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Output Over-Current Protection
An over-current condition on either the 28.6 Vdc or 14.2 Vdc outputs caus-
es the total supply to shutdown and try to restart. If the over-current con-
tinues to exist, the power supply will 'hiccup' until the overload condition
is removed, and will not be damaged by the overload. The 28.6 Vdc out-
put is protected by a primary current sense method such that its current
limit point varies depending on the load on the other outputs at the time.
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 28.6 V and 14.2 V dc outputs are protected from continuous over-volt-
ages by detection circuits that cause the supply to shutdown and then try
to restart itself. 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 14.2 Vdc and the 5 Vdc outputs are protected by crowbar cir-
cuits.
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 a TTL compatible output ca-
pable of sinking 1 mA, and is routed to the Station Control Module. The
active-low state indicates ac operation. For the nominal 120 Vac operation,
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 voltage
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.
68P81011Y31-O
03/10/06