For an experiment a client needs a 3.3V/15A or larger supply, must be linear. Checked the usual suspects and at 10A there's pretty much the end of the rope these days. 5V/25A could be useful if I can get in there and hack it, should have enough SOA to deliver 3.3V/15A.
Does anyone know where to get one? Can be used/salvaged as long as it works and is linear.
A switcher might work if it has next to nothing in ripple. Most are
50-100mV, won't work. I want to avoid having to build a post-regulator. But if nothing's there, man's got to do what man's got to do.
Dang, I had two supplies 5V/30A until my wife said it's time to clean up the garage :-(
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Regards, Joerg
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Lostgallifreyan wrote in news:Xns9B696841912Bzoodlewurdle@216.196.109.145:
I should add that if you do it this way you can even use the commoned Adj pins to sense the far end to ensure you're really getting the set voltage there, with a small adaptation.
If I have to do that then I'll do it. But I found that load change reactions of such switchers when loaded with unorthodox loads (mine somehow always are ...) will usually be in the same level range as the ripple. No matter what the marketing guys put on the datasheet.
Yeah :-(
But: When we walked the dogs this afternoon a neighbor offered us his grandfather clock. I just would have to repair it. My wife was tempted but I remained firm, I just don't want to have yet another project on the never-ending honey-do list.
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Yes, plus you'd have to crank up the switcher a little. Meaning they either must release the schematic (which they won't) or it'll be a hack. The usual, find PWM chip, hope it's not filed off, try to decipher part #, get datasheet, flip red button on the Weller.
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Joerg wrote in news:sPkZk.1472$ snipped-for-privacy@flpi144.ffdc.sbc.com:
This is what transformers are for. >:) That aside (and the less said about the size they'd have to be, the better), this sounded like laser drive the first time you mentioned low volts and high current with no ripple, now it looks even more like it (gas this time), though I think if it had been either you'd have been after current control and some different voltages.
Joerg wrote in news:ohlZk.1475$ snipped-for-privacy@flpi144.ffdc.sbc.com:
I second that one. It might even be possible to use some linear regulator for the reference and internal op-amp, if it lets you get at them the right way.
I once tweaked a computer SMPU to get about 7 volts out of the 5V line. I traced a pair of resistors that were a divider, and shifted the value with an added preset pot. It worked ok. I looked into trying it with another, and no such easy trace existed, so it's pot luck. Yes, really said that. Anyway, if you can do this, you might tweak it high enough to let ganged LM338's work fairly efficiently fed off the was-supposed-to-be-5V line.
Well, that's her next birthday present sorted - a clock repair tool kit.
You mean that /she/ can't design you a 3.3v 15A linear supply? I won't ask what she *is* good for :)
3.3v is /just/ within the minimum voltage spec of a "standard" 15A lab variable power supply. Do you not have Government Surplus Stores? You might pick up one there for a song (and a hernia..).
It also, (if my memory at twenty to two in the morning serves me right), is the voltage used on early Cray and CDC Cybers to power the ECL chips. So, if you could pick up a surplus power supply for one of those, you would have amps and plenty.
Talking of which, I do happen to have a couple of 5v 50A modules from a Cyber mainframe. 110v in. Not much use to me here in the UK but, hey, I have a barn and what else would I put in it? Hey..barn..oh, never mind. it's late.
However, if you do go to the hack-a-5v-supply approach, you may simply be able to offset the *ground* reference of the regulator by a couple of (negative) volts. With any luck, you will be able to use the same transformer/transformer winding as the main positive output, which will mean that you will *decrease* the offset voltage as the load increases - thus potentially *reducing* the ripple. You could even end up with a power supply with ripple that decreases as load increases :).
DJ Delorie wrote in news: snipped-for-privacy@delorie.com:
Nothing, it was a joke. If he'd applied it in concept, the total voltage from in to out would be same as with one. But the ripple might be better, I don't know, haven't calculated it. Three-terminal variables have better regulation than the fixed types you mention anyway, do if you must chain them, do it with variables, you get to choose your voltages to share the waste heat load better, as well as using fewer devices for a given ripple reduction, but in the end I think it's better to use as few devices as possible in a chain, if it were necesary to do what you suggest, people would do it, and it's rare. I've seen two chained, to get a low rail off a higher one, but not for ripple reduction.
Well, sure, if I build the whole chebang myself I know how to do that. But that's what we try to avoid. There used to be off-the-shelf supplies like this and I actually had two of those (until a garage clean-up day mandated by SWMBO).
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Regards, Joerg
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