A schematic for a 3.7 volt power supply

[p3aul]

I'm getting tired of looking all around the house for chargers for cameras, ebooks and cell phones I want to build a power supply that will deliver 3.7 volts DC at 4 amps. I found a transformer(12v), center-tapped that will deliver 4 amps. I found the transformer at MPJA but they don't seem to have a regulator that will produce 3.7 volts at 4 amps. I know that I will have to have a monster of a heat-sink and probably a fan. I need a schematic. Of course I will breadboard this project first anyway. Can anyone come up with any thing?
Thanks,
Paul

[I_Daniel]

[url]http://www.google.co.za/url?sa=i&source=images&cd=&cad=rja&docid=Va2luam6GTRBmM&tbnid=gEcgUGRgFyfSUM:&ved=0CAgQjRwwAA&url=http%3A%2F%2Fwww.circuitstoday.com%2F13v-5a-adjustable-regulator-using-lm338&ei=FVsnUabOLcOwhAec44CIAg&psig=AFQjCNEaGiiqvGgxQsEbVubVRSKV0suPNg&ust=1361620117788135[/url]

The above is a link to a LM338 5 amp adjustable regulator 1.5 Volt -->

(The 13v they mention is the maximum output voltage based on their transformer and not the minimum which is adjustable with the variable 4k7 Ohm resistor.

You can always check the output with or add a voltmeter and adjust the output to what you require.

If you require a circuit using a few resistors, large smoothing capacitor, a zener diode/one sensing transistor (BC147 etc) and a 2N3055 power transistor then I could possibly give you a circuit diagram of an old variable Citizen Band home base radio's power supply that will handle 5 amp or more.

The LM338 however does have overload and overheating control built in.

My problem is I will have quite a search for where I stored those old circuit diagrams and some of my books were never returned so rather go for the LM338.