Service Manual

GSM-204-323
MicroBCU power supply module (BPSM)
31st Oct 01
Technical Description: Horizon macro outdoor
68P02902W02-A
CONTROLLED INTRODUCTION
Tech. 4–37
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The BPSM is a switching type dc/dc power converter that converts the cabinet
+27 V dc power to the following regulated dc outputs:
 +3.3 V ± % at 10 A (full load current)
 +5 V ± 2 % at 10 A (full load current).
 +12 V ± 5 % at 4 A (full load current).
 –12 V ± 5 % at 2 A (full load current).
Internal BPSM circuits monitor the +3.3 V, +5 V, +12 V and –12 V outputs for the
following purposes:
 Output voltage regulation.
 Overvoltage protection - provides shutdown if the output voltage exceeds
1.1 to 1.2 times the rated output.
 Overcurrent protection - maximum output current has the following limits:
– 1.1 to 1.8 times full load rating of +3.3 V output.
– 1.1 to 1.8 times full load rating of +5 V output.
– 1.25 to 2 times full load rating of +12 V and –12 V outputs.
Circuit protection
Additional internal circuitry protects the BPSM:
 Input dc reverse polarity protection, achieved by an input series diode.
 Thermal protection by automatic BPSM shutdown. Normal BPSM
operation resumes after BPSM temperature returns to a safe level.
 A 10 A fuse is located near the backplane connector.
LED display
An active (green) LED mounted on the front of the BPSM is lit when all output
voltages are present and within specified limits. A functional diagram is shown in
Figure 4-22.
ig.275.rh
Green
LED
Power converter and
system monitor
VOUT (+5 V)
VIN (+27 V)
VOUT (+3.3 V)
BACKPLANE CONNECTOR
VOUT (+12 V)
VOUT (–12 V)
Figure 4-22 Functional diagram of BPSM