Description Of Internal Sequences In The Power Supply Unit - Siemens S5-155U System Manual

Power Supply Units
4.3.5
Description of Internal
Sequences in the Power
Supply Unit
Behavior upon failure of the
system supply
When the system supply fails
If the 5 V supply drops below
the 4.75 V limit
Redundant data backup
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Given in this section is background information on internal sequences
in the power supply unit.
The behavior of the power supply unit after a system supply failure is
governed by the duration of the failure:
IF the system THEN...
supply failure...
lasts up to the PSU output voltages are within tolerance
20 ms, ranges; no indication appears on the front plate
and no signal is sent to the S5 bus.
lasts longer than a data save routine is initiated on the CPU/CPUs
20 ms, and an output inhibit is issued.
If the 5 V supply drops below the lower limit (4.75 V), the power
supply also activates the output inhibit, and the data save routine on
the CPU is thus initiated.
Your CC and EU 185 are provided with a lithium battery for data
backup, and the power supply unit also contains a rechargeable
battery.
In the event of system supply failure or switch-off, data backup is
guaranteed by the lithium battery and, in the event of battery failure,
by the rechargeable battery which is constantly being charged to its
full capacity.
After replacing a defective lithium battery, the new one resumes data
backup and on exchanging the battery you should acknowledge the
error indication.
As the rechargeable battery is also removed when the power supply
unit is replaced, data backup is temporarily performed by the lithium
battery.
System Manual
C79000-B8576-C199-03