Battery charger and power selector

picaxe battery charger

I must confess that I've been runing away from analog design for the last 5 years. Now I was forced to change my bits by coulombs, and it doesnt look very funny!

I have to create a power supply with the following specs:

230V AC mains supply
12V 400AH lead acid batery UPS
outputs - 12V 4A unregulated(to avoid efficiency loose with another regulation step)
12V 2A regulated
5V 4A regulated

Baterry charge can take up to 4 days, so a Max 8A float voltage charge should work.

The main idea is not very hard:

First a converter from 230V AC to 12-15V DC. That will be used for the baterry charger circuit and also for the 12V unregulated output when mains power is present.
Then there must be a charger circuit for the battery and a power selector to choose the source for the power output. That is the switching from Mains supply to battery on power failure, and total disconnection if lead acid battery is depleted to avoid overdischarge.
The last part is the 12V and 5V regulators.
I will also include if time permits a ADC for battery monitoring, but that is the easy part.

Switching mode power supplys must be used for efficiency.

I also only have 2 weeks for doing the prototype and SMDs are also a nightmare.

If someone know a not-very-expensive made solution my problem is solved...otherwise:

Any recommend charger ICs?
Any recommend power selector ICs?
Any recommend changes or stupid-corrections to my design idea?

Thanks!

baterry charger

I would use PICAXE-08M microcontroller (8-pin DIL, 10-bit A/D+I/Os) and 2 x P-channel MOSFETS to switch/select power from the mains and battery - see an example here:

Another PICAXE-08M and an external PNP or P-MOSFET can be used as "intelligently" controlled constant-current source to charge battery ..
Using PICAXE is not difficult and will make sure that the project is completed within 2-weeks ..

Rgds,
IanP

power selector

There are a few bulk charger circuits at:
**broken link removed**

or switching supply versions at:
**broken link removed**

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