AVR-Chat

I like the KISS approach... Depending on your needs, you can
use a SPDT relay with a mains powered coil. When the power
is on, the relay is energized and the N.O. contacts closed to make
the DC circuit from power supply to your MCU board.
(common to the MCU board, NO to the power supply +
and NC to the battery +).
 If the mains power cuts out, the relay will release and make
the NC contacts circuit which can is wired to the battery. A big
electrolytic cap across the DC input can be selected to maintain
the supply voltage while the relay switches over so that your
board doesn't drop out and also to help absorb the switching
voltage spike.

Hugh


jaythesis wrote:

>hi!
>
>does anyone have a circuit design on back-up power supply? like if 
>the main power is cut-off, the battery automatically takes over to 
>supply the MCU. can i have the design?
>
>thanks in advance.
>
>-jay
>  
>