[time-nuts] paralleling regulator redux

Didier Juges didier at cox.net
Tue Nov 13 20:43:46 EST 2007


It's been my experience that most low-dropout regulators are worse than the
older generation high-dropout, not only for noise but also for ripple and
transients rejection, probably because of the unfavorable topology of a
power PNP transistor as the pass element. It has low gain and low FT, and
yet the circuit is naturaly unstable unless particular decoupling caps are
used, so compromises in the loop response have to be made, resulting in high
noise. It's possible the reference internally is quiet, but the regulator
itself is bad.

I guess for most applications it's OK, so unless pressed by the market, the
vendors will do what sells. 

Didier

> -----Original Message-----
> From: time-nuts-bounces at febo.com 
> [mailto:time-nuts-bounces at febo.com] On Behalf Of Bruce Griffiths
> Sent: Tuesday, November 13, 2007 12:24 AM
> To: Discussion of precise time and frequency measurement
> Subject: Re: [time-nuts] paralleling regulator redux
> 
> Didier Juges wrote:
> > The point of these improved acuracy regulators is that in 
> most cases, 
> > trace resistance (the PWB) is sufficient as a ballast, so 
> there is no 
> > need for a separate component (if you have enough room for 
> the trace 
> > :-)
> >
> > Didier KO4BB
> >
> >   
> But they are still noisy.
> Note some plots are for 1V output.
> 
> bruce
> 
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