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FAQ01990 of Power Supplies FAQ

FAQ No. FAQ01990

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The output voltage decreased while Power Supplies are in use. What is the cause of the problem and solution?


OperationOutput from
the Power
Supply has
Surge or other overvoltage has been
applied externally (e.g., load) to the
output side, activating overvoltage
Add a varistor and diode to the source of
the surge, and make sure that overvoltage
is not applied to the Power Supply's outputs.
The incorrect input voltage (applying
100 V when the setting is 200 V) has
been applied. (If 100 V is applied
when the voltage is set to 200 V,
although damage will not occur
immediately, damage will occur if
use is continued.)
Make sure that the input voltage is the same
as the voltage set using the selector terminals.
The internal circuits may be damaged. Replace
the Power Supply.
Output from
the Power
Supply has
stopped (close
to source of
vibration or
Cracks have occurred in the internal
soldering due to vibration in the
operating environment, preventing
electrical conduction. (The vibration
and shock are particularly close to
the contactor.)
If vibration occurs during operation, check the
installation location and reduce vibration or
consider inserting vibration-proof rubber
between the Power Supply and its mounting
Output from
the Power
Supply has
(close to
source of
strong, high-
Damage has occurred due to impulse
from the input line.
If impulse occurs in the input line, separate the
Power Supply's input line from the source of
the impulse. If separation is not possible,
connect a varistor either to the source of the
noise or to the Power Supply's input terminals.
Also incorporate a fuse that will provide
protection if the varistor is short-circuited and
Output from
the Power
Supply has
(the fan has
The fan's life has expired, preventing
forced cooling, and the internal
temperature has risen activating
overheating protection.
Perform periodic maintenance on the forced
cooling fan and replace the fan promptly if any
fault in the fan is found.
The fan bearings have been worn
down due to the operating
environment (e.g., dust or dirt).
Perform periodic maintenance on the forced
cooling fan and make sure that there is no
dust or dirt present in the operating environment.
The output
is unstable.
The terminals have become loose.Retighten the terminals to the specified torque.
The output
The life of the internal components
has expired.
The service life of the Power Supply's built-in
electrolytic capacitor depends on the ambient
temperature and load rate, and its structural
life depends on the operating environment
(vibration, shock).
Replace the Power Supply together with other
Power Supplies that were purchased at the
same time.

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