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Cordless Phone Backup

Discussion in 'Electronic Basics' started by Animesh Maurya, Oct 14, 2003.

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  1. 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.

    Circuit is here

    My problem is that Iam using Panasonic KX-TC1000BXB which is having a
    9V adapter rather than 12V, so what changes should be made in the
    circuit for proper operation.

    Thanks in advance
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