[time-nuts] Parallel voltage regulators

Magnus Danielson magnus at rubidium.dyndns.org
Thu Oct 25 18:59:47 EDT 2007

From: Bruce Griffiths <bruce.griffiths at xtra.co.nz>
Subject: Re: [time-nuts] Parallel voltage regulators
Date: Thu, 25 Oct 2007 17:42:51 +1300
Message-ID: <47201ECB.6050702 at xtra.co.nz>

> Don Collie wrote:
> > Hi Tom,
> >     If you really want to regulate the oven`s supply voltage, my National 
> > Voltage Regulator handbook shows that the LM317T will supply over 2 Amps, 
> > with an input/output differential of between 5, and 12.5 Volts. A single one 
> > of these should do the job OK.
> > Cheers!,.................................Don Collie jnr.
> >
> >   
> Never rely on typical specs always use the minimum spec which is 1.5A
> not quite enough.

You want design-margin. Some of that toll will be in less than optimum heating,
some will be in less heating in the first place (compared to upper limit) and
for a power regulating aspect, headroom allows better regulations.

In one design we had to parallel the regulators since the regulator the
designer put in just barely was able to regulate the CPU core voltage.
It worked, but at just rebooted at some vauge point an the memory tests.
What actually happend was that as soon as it started to actually do anything,
the regulator was running at its limit and output voltage dropped as the
current was rising and the voltage supervision pulled the RESET.

That's what you get from reading the typical reading on the CPU current and
match that with the maximum rating of the power regulator. A no margin design.
That designer had a few more flaws which was creeping around in that design,
but let's not bring that can of worms open here. :)

The 5A LM338 will be just fine. Infact, you can pull 8A out of it under
certain conditions.


More information about the time-nuts mailing list