Driving a Voltage Regulator with PWM

[flotulopex]

Hi Ioannis,

I am making a lead-batteries charger.

In my opinion, it is not necessary to control the full voltage range of the batteries that need to be charged.

Important is to control the charging voltage (2,35V/element), the floating voltage (2,26V/element) and, of course, the timing (n hours for charging -depending on battery capacity- and then go to "float" or "trickle" mode).

So, if you have i.e. a 12V lead-battery (= 6 elements), the charging voltage will be 6x2,35V=14,1V and the floating voltage will be 6x2,26V=13,56V.

Roughtly, the voltage range to control is quite narrow: less than 1 volt. Thus. this should avoid the use of an OP-Amp. The current is limited by the transformer's capacity.

So this is what I would like to achieve now. It could look like this:
<img src="http://www.picbasic.co.uk/forum/attachment.php?attachmentid=1806&stc=1&d=118293647 1">

[Ioannis]

On the schematic you have to power with more that 15Volts. 2950-5 needs at least 0.45 volts at the input above from 5V. If your battery is discharged and request more current, the transformer might drop the voltage bellow 15V.

The circuit is quite economical but I am afraid that is quite a compromise too.

I have attached my idea in a hand schetch (sorry, no CAD here!).

Ioannis

[flotulopex]

CAD is not necessary - your drawing is well done

You're right, the Zener is going to be an 8,7V since I don't have another under my hand...

Maybe I'll go for your solution.

Have to make some trials.

Thanks a lot.