Siemens S5-135U/155U - Manual (Page 115)

4-49
System Manual
C79000-G8576-C199-06
4.3.5 Description of Internal Sequences in the Power Supply Unit
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 supply failure... THEN...
is shorter than the stored energy time
for power failure the PSU output voltages are within tolerance
ranges; no indication appears on the front plate
and no signal is sent to the S5 bus.
is longer than the stored energy time
for power failure a data save routine is initiated on the
CPU/CPUs and an output inhibit is issued.
To ensure data backup, your CC and EU 185 are provided with a lithium
battery, and the power supply unit with a rechargeable battery.
In the event of system supply failure or switch-off, data backup is provided
by the lithium battery and, in the event of battery failure, by the rechargeable
battery which is permanently recharged to remain constantly operative.
After replacement of a defective lithium battery, the new one resumes data
backup and you must acknowledge the fault LED on the front panel.
As the rechargeable battery is withdrawn during the replacement of a power
supply unit, data backup is temporarily performed by the lithium battery.
Behavior Upon
Failure of the
System Supply
When the System
Supply Fails
Redundant Data
Backup
Central Controllers and Expansion Units Power Supply Units