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

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.

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Regards, Joerg

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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

*did* for the purposes of my example.

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?

"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 :-)

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Regards, Joerg

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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.

:-)

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Regards, Joerg

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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.

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Regards, Joerg

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

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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.

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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

What I really love with my GDS-2204 is the 25K sample memory. I could never really live with Tektronix' paltry 4K because I do a lot of pulse-echo stuff. Also, the screen is really, really bright. If they just hadn't chosen those bonbon colors.

Hey, teach your students analog stuff. We are losing those folks to retirement (or worse ...) left and right.

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oopere wrote in news:gh61j6$jof$ snipped-for-privacy@defalla.upc.es:

Oh, I thought you were a Yorkshire man from the the address. :) They might state an address of 'oopere' with some pride..

I know Excess Solutions has linear supplies, though I didn't see them on the website. They usually have one or two of a type of linear, so maybe web sales don't justify the time to enter the item. I go there for specifically for linears, though I buy switchers once in while.

The last time I was there, I got a Voltek (really Volgen) EX 50w, 24V,

2.1A, made in Japan switcher, new in the box, for $6. (Digikey sells the same brand for about $50). Excess Solutions is the last surplus shop in the bay area as far as I am concerned. Yeah, Weird Stuff and Halted still exist, but they have way too much junk. I go there and never buy anything, so I just stopped going.

I'd be leery about doing internet sales with Excess Solutions. Their bins are often mislabeled. I was looking for cables with SMA connectors on them. Now usually the problem with Excess Solutions is every freakin' RF connector is labeled SMA even it is something else. That day, there were no cables with SMAs on them, or the cable had no impedance labeled.

They had a box full of Tek adapters for $5, none of which I really need. However, they had a Tek tunnel diode pulser for $5 that I couldn't pass up.

Now you got me in the mood. I think I'll make a run today and will email or post if I find what you need.

Halted is (was?) the only one left here near Sacramento but I only went once. Not much there that I found useful.

Same with power supplies even at Digikey. When it says "linear" and then something like 80VAC-260VAC it was pretty clear it's really a switcher. I guess the folks doing web entry aren't engineers ;-)

I bet John Larkin would like to know if you see something like that again.

Thanks, no need anymore, JW pointed me to MPJA. They and some others still have a few huge 5V supplies so we are covered. To my surprise even Digikey has a few left, no idea why they did not show up there yesterday.

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