Occasionally I need an LDO and I hate those things because of inherentinstabilities. So I usually do not use commercial ones. My own LDOdesigns sometimes contain depletion mode FETs when I don't have thespace for a charge pump or radio silence is required. Downside is thereseem not to be many folks doing that, not much of a variety of FETs topick from and the bigger depletion mode devices cost over a buck. Ouch.Why are there no commercial LDOs with depletion mode devices? Or arethere? At least I am not the only one with such "wicked thoughts",there's even some in Arizona:Of course there is the issue of channel saturation but for smaller stuffthey work.-- Regards, Joerg

I seem to recall that there's something about the construction of the usual power FET that makes it only work in enhancement mode -- so a depletion mode power FET would be considerably harder to make. This is probably why they're expensive and rare.The idea of an LDO with a charge pump so that you can go common-source is interesting -- are there any commercial devices that do this?-- Tim WescottControl system and signal processing consulting

Why no depletion mode LDOs?

May 06, 2012 102 Replies

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josephkk 14 years ago

prick exclude

Sub-par. And not in the golf sense.

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josephkk 14 years ago

scripts

I have had problems at 10 MB and success at over 100 MB. YMMV

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Jim Thompson 14 years ago

My copy of WSFTP is dated 1995, and I can't _ever_ remember a problem. ...Jim Thompson

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