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Cordless Phone
Backup |
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Normally
the base of a cordless phone has an adaptor and the handset has
Ni-Cd cells for its operation. The base unit becomes inoperative
in case of power failure. In such conditions, it is better to
provide a backup using Ni-Cd cells externally. Here is a simple
circuit which can be used with cordless phone SANYO CLT-420 or
similar sets.
The working is simple. When AC mains is present, Ni-Cd cells are
charged through IC LM317L, which is wired as a current source.
Also, diode D3 is reverse-biased, which keeps Ni-Cd cells isolated
from positive rail. When AC mains goes off, the Ni-Cd cells
provide supply to the cordless phone base unit through diode D3. A
green LED is used to indicate the presence of AC mains.
Each Ni-Cd cell costs around Rs 34, and the cost of the backup
unit, including the box and cells, would not exceed Rs 300. Hence
the circuit is well worth the investment
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Click
Here For Circuit Diagram
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