Cordless Phone Backup

Normally the base of a
cordless phone has an adaptor and the handset has Ni-Cd cells for its
operation. The base unit becomes in-operative in case of power failure.
Under such conditions, it is better to provide a backup using Ni-Cd
cells externally. Here is a simple power supply back-up 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
cel ls 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.

Sorry, comments are closed!