Need linear supply 3.3V/15A or 5V/25A

Those aren't LDOs. There is an imaginary sign here in the hallway: "No cheap beer and no LDOs beyond this point".

A well designed regulator will completely kill the ripple in just one stage, no need to chain them. All you really need is a LM317 and a few beefy transistors. Plus a huge heat sink, #10 screws, and so on. That's what I want to avoid.

Not around here :-(

That's the kind of machine my two supplies came from.

Linear supplies? Why does everything useful have to be 6000 miles away ...

Usually when I do that I also try to pry off some of the secondary windings of the transformer, whether on a linear or a switcher. Makes everything run happier and less hot.

Addendum: If anyone is aware of a huge surplus place in the US (preferably with a web site) that still has mainframe era stuff let me know. That's how I used to get such supplies but it was in Europe.

The 78xx-series are not LDOs, but...

Lower ripple at the output is the result. Each regulator adds xx dB of ripple rejection.

No need for all those big caps, just the input cap will do.

Cheers, James Arthur

True, but he was asking about 78xx ;-)

(They're spec'd near 70dB each, which ain't bad.)

Cheers, James Arthur

Yeah, I know, but I figured everyone would know what those devices

With adjustable LDOs you could use a switcher to get to 6v (or less), then two LDO stages to get to 5v, minimizing heat loss.

:Hello Folks, : :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 :-(

It is unlikely you will find off-the-shelf linear PSU's rated at 3.3V.15A these days so the best I can suggest is a medical grade switcher with around 80mV p-p ripple, eg. VRPS-75-3.3.

Excess Solutions in Milpitas, but geez, I haven't seen linears that big. All I own in linear land with that much current is 10A. I'd hate to pay the freight on those big Lambda linears.

BTW, while everything thinks in terms of LDO, I always thought they should make HDOs. What is an LDO but an amp and a pass device that acts like a resistor. If a fet pass, it is in the linear (triode) region. This is not the best place to be if you want "natural" regulation. OK, by natural, I means what you get when the hit to the system is above it's bandwidth, so all you have for regulation is that of the capacitance in the system, i.e the thing resistive to movement. Now if you had a HDO, then the fet could be saturated. With a whack of capacitance from the gate to ground, the device can regulate at high frequency to the tune of how much transconductance you have in the fet.

In chip design, I like to look at how the circuit will react at high frequency, i.e. nothing but junction capacitance. Often you can add parasitic devices that balance capacitive paths and thus improve PSRR.

Maybe I shouldn't try to explain this kind of stuff after midnight.

How about this one?

EA-PS 3016-40 B, should work in the US too, costs in AT around

- Michael Wieser

"Joerg" skrev i meddelelsen news:OCkZk.8406$x%. snipped-for-privacy@nlpi070.nbdc.sbc.com...

You want "Linear" without the "Linear Look & Feel"?

You may have a look at this

Pere

Oh, I want the linear feel, just not this much feel :-)

Thanks, checked their power supplies. The usual, all 31 they've currently got are switchers. The Coutant supply at 5V/100A ain't a bad deal at $50 if someone needs real muscle.

:-)

That's too much ripple. No big deal to filter it out but in this setup we've found that no matter what you do a few microamps of ripple will find its way into the signal path.

There used to be 5V/30A supplies. I know that for a fact because I had two until a couple years ago. But, gone ... I just didn't know that I'd ever need something like that. They were made in California, black and gold-brushed enclosure but can't remember the brand.

Hooray! Thanks! Looks like it might be a classic uA723 design so a hack should be a piece of cake.

Thanks. A bit pricey and not easy to get into the rack. But I am quite pleased with the Instek brand, got a scope from them. Maybe we'll get one of those 0-18V supplies for bench experiments.

I also have had good experiences with Instek scopes. We recently equipped a students lab with them. Good quality vs price. Recently I had the occasion to briefly test one of the power supplies and they looked quite good -although not that cheap.

Pere

Thanks. Interesting, I've worked together with Elektroautomatik in the