[time-nuts] Parallel voltage regulators

Bruce Griffiths bruce.griffiths at xtra.co.nz
Thu Oct 25 02:20:12 EDT 2007

Don Collie wrote:
> Bollocs, Bruce! If National say it will do it, you can bet that it will. An 
> LM338K will do the job too, but in my opinion it`s overkill, and in the 
> event of a short circuit on the output of the regulator the current for the 
> LM338 will only be limited to [.......he gets the book......] 8 Amps [Typ], 
> as against 2.2 Amp [Typ] for the LM317T. This would probably be too much for 
> the transformer, rectifiers, and smoothing capacitor, effectively meaning 
> that you would have no current limiting. If the input/output differential 
> was kept in the range of 5 to 10 Volts, while the oven was stabilising, and 
> the LM317 had an adequate heatsink, it would do the job nicely [and cheaper 
> too!] Actually, it wouldn`t matter if the oven supply went unregulated while 
> the temperature was stabilising, because you wouldn`t be using it for 
> measurements during this time anyway - or is that a bit radical!?
> All the best!,..................................................Don.
> ----- Original Message ----- 
> From: "Bruce Griffiths" <bruce.griffiths at xtra.co.nz>
> To: "Don Collie" <donmer at woosh.co.nz>; "Discussion of precise time and 
> frequency measurement" <time-nuts at febo.com>
> Sent: Thursday, October 25, 2007 5:42 PM
> Subject: Re: [time-nuts] Parallel voltage regulators
Show me where that is actually guaranteed on the datasheet.
Only the inexperienced and the gullible fall into the trap of assuming
every regulator (or any other device) will meet its typical specs.
The designer of this particular regulator actually cautions against this
cavalier approach to design.

If you worried about the transformer a simple fuse (resettable or
otherwise) will surely cure that problem.


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