Spagbol

Unitrode produce a switch mode IC specifically for Lead acid charging, the bq2031. If you still want to use one of those PWM ICs you mention you could always have a look at the application note for the bq2031 to see how it works: http://focus.ti.com/lit/an/slua017/slua017.pdf

Presumably output taken from top of C7 in new circuit rather than emitter of Q4, just to clarify.

Not sure I understand about Q1s emitter, looks ok in original cct to me. It is a safeguard against there being no -5v rail isn't it? So when there's no -5v the transistor (Q1) conducts and pulls U2 to ground so there's no drive to the output transistors??

Aha, suppose I must read thru the thread again. Nice photos by the way, I've never made a PCB before but maybe I will try it.

What's the Q2 emitter modification you mention? I've skimmed this thread, maybe I missed something? I've built the Op-amp bits with a pair of TL082s with their supply rail clamped at 22v by a zener. So far so good, but not sure how to change the output stage to give it some voltage gain? Audioguru: thanks for the suggestion for temp sensing with a diode, will have a go at this once I get the PS working.

Could try putting a bulb in series between the rectifier/cap and the regulator. (eg a 12v/21w car brake bulb?). Shouldn't affect the cct at low current but if you get a short it'll light up and take some power away from the regulator!? Haven't tried it mind....

Sallala, before you blow up another transistor...... If you test with a 1 Ohm resistor at 2-3 volts as you say, the 2N3055 will have to disspate a lot of power! (~100W!!) You really need to use more than 1 2n3055 (like in the cct in the thread for the 5A version) and they will need a very effective heatsink!

Don't forget the diodes in a bridge only conduct up to 50% of the time, halving the average current, so you might get away with 1n4000s, wouldn't use the 4001s though as they'd only be good for about an 18v supply!

Hi all, I like the design for this PSU and would like to build it, but with some changes. It seems only U2 needs a high supply voltage to drive the output to 30v, U1 & U3 would be happy with a lower supply voltage. I'm wondering about changing the transistor o/p stage to have a voltage gain of 3 and then clamping the opamps supply voltage at say 20v using a zener so that any stock opamps can be used? (I have loads of TL082s and LM358s etc. so I'd like to use those). I have 2 transformers I can use, a 24v ~100va and a 2x14v ~300va, as this limits the max o/p voltage I thought I'd add a preset pot to the top of P1 to limit the max output voltage according to what the transformer can cope with? As I'm using dual op amps I thought the leftover amp could become a comparator with a thermistor for a thermal shutdown if the pass transistor becomes too hot? I'm a bit rusty, so any comments on changing the transistor o/p stage (if feasible) would be welcome!