The dissipation will remain the same irrespective of the type of series pass
device used (to all intents and purposes) - I'd probably choose  plastic
power bipolars, as they're cheap, have plenty of current handling
capability, and don't need to be isolated from their heatsink.

Chris

----- Original Message -----
From: "A.J. Tufgar" <tufgaraj@MUSS.CIS.MCMASTER.CA>
To: <PICLIST@MITVMA.MIT.EDU>
Sent: Thursday, November 28, 2002 5:57 AM
Subject: Re: [EE]: 15, -15V @~3A PSU.


> Sorry I'll clarify a little.  :)
>
> I'm assuming AC mains in, so I need a step-down, etc yes.
> I don't need variable but I also will be using 12V, -12V .1A regs on it
> as well, so I prefer the 18V, -18V transformer Chris suggested.
> I would prefer to keep noise down to <5 mV.
> Load is varying anything from 3ma to 3A.
> Efficiency isn't really important but I'd like to get away with smaller
> heat sinks, but oh well if not.  :)
>
> I don't mind describing the application but I wanted to keep the post
> as short as possible.
>
> Could I use a hexfet as a pass-transistor so it won't get as hot or is
> this a bad idea for some reason?
>
> Thanks,
> Aaron
>
> >There are a zillion ways of doing this (most very similar)
> >Useful info would include:
> >
> >- Variable or fixed.
> >- If variable, tracking or independent.
> >- Do you have existing input supply or transformer etc? If so what?
> >- What is the load?
> >- Noise important.
> >- Efficiency important?
> >
> >The better people understand your need the more likely it is that they
> >can
> >help
>
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