Question regarding 78xx series devices

Not everything Larkin says is bad, but when it is and it's twisted to make it seem good, it deserves to be looked at through a Rochelle salt crystal.

John Fields

Well I want to see where the R's and C's are. I've done thing's like that, with lm317/337.

But I agree at the moment who knows. I hooked up "that" circuit w/o ground today....

Hmm. OK I better post the whole thing (there's not much) here tomorrow, certainly a "beer"* for every addition component I end up adding.

George H.

I wouldn't say bad. But much of what he posts here is a bit stupid. He implies that XO's and huge FPGA's are the universal loads. What???

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Geesh John F., I don't feel that way at all. I think JL is confused (polite, euphemism for wrong) about some things, but it's not a big deal to me. I mean there's some chance I'm wrong instead. Say 10%, whatever. (50%, if it's important to you, you spend time and become expert.) And 90% of his output I find stimulating... (circuit/ science/ life wise...)

George H.

The subject was minimum load and adjust pin currents of regulators. The load is relevant.

I do lay out a modest board now and then, but it takes weeks to lay out a serious multilayer BGA-studded board, so I have people who do that for me.

I did this, schematic and layout, in a weekend, which is about my attention span for a layout.

But no BGAs. I don't recall ever routing a BGA, or touting my ability to do so. I certainly could; there's nothing special about BGAs except that they tend to have a lot of connections.

I sometimes lay out breadboard sorts of PCBs, to test circuit ideas. It's not practical to breadboard some things any other way.

When I do one of these, I walk around and see if anybody else might want me to throw in a test circuit for them. When the boards come in, I shear them up and hand out the pieces.

You just don't like me, so you irrationally whine about anything that I do. That includes making suggestions to improve your circuits.

But most of it is good. I rarely post the bad stuff, unless it's especially interesting.

Those are the key elements. The reservoir caps handle load current imbalance in the very short term, leaving zeners to take care of all remaining imbalance. Enough gotchas to make many uncomfortable, but it does work.

NT

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well it started with him mentioning using two stacked regulators to get

-Lasse

Seems to me that would only affect opinions that were polarized in the first place. ;-)

--sp

I'd be more inclined to rail-split with an op amp and a couple of BJTs for a class-B buffer, like an LM324 on steroids. ;)

Probably more expensive than your approach though.

It would sure be nice if the TCA0372 came in a proper power package--it's a perfect rail splitter except that it runs really warm.

Audio power amps sometimes use a fun rail-balancing trick--you take an inductor with one end at ground, and switch the other end alternately to V_CC and V_EE. Any imbalance makes DC flow in the inductor to null it out, without a lot of loss.

Cheers

Phil Hobbs

Can you hang reservoir caps on the output of that? If not the whole thing consumes upto twice the power, depending on the current imbalance.

NT

Sure. You just have to pay attention to the frequency compensation.

Plus you can put the rail splitter ahead of the regulators.

Cheers

Phil Hobbs

I saw a switching rail splitter somewhere once. It was just an inductor switched alternately between the rails, to common.

I mentioned that just upthread. It's a cool idea.

Cheers

Phil Hobbs

As per my experience 7815 will not work if you connect the 9V input to it.

The input must be more than 15V. But you can make it 18V by putting the positive output from the output of transformer.

Your other setup is good but look for this. Share your setup schematic here if you can.

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