power supply

[integra]

I am trying to build a 5V power supply with battery back up for one of my projects that involves TTL ICs. I need help in the battery change over part due to the following reasons:

1. The battery that i have is a 6V (5Ahr) rechargable lead acid cell (i cannot directly supply it to the ICs since Vccmax=5.25V)
2. I need a glitch free change over circuit.
3. I am not sure about the current that should be provided for trickle charging the battery.

pls post ur valuable suggestions.

 

[Hero999]

Us an LM317 regulator to charge the 6V lead acid battery to about 7V and a low dropout regualtor like the LM2940CT-5.0 to supply your digital circuit from the battery.

Don't worry about limiting the battery charge current, the LM317 has built-in over current protection.