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From: jeff@hpuplca.nsr.hp.com (   Jeff Gruszynski  )
Newsgroups: sci.electronics
Subject: Re: High current and PCBs/Question
Message-ID: <12780005@hpuplca.nsr.hp.com>
Date: 7 May 91 21:43:04 GMT
References: <846.2824a3ea@zodiac.rutgers.edu>
Organization: Hewlett-Packard Pleasanton Ca. Sales
Lines: 37


>/ hpuplca:sci.electronics / svanderschyf@zodiac.rutgers.edu /  6:31 pm  May  5, 1991 /
> Here's another one-
>
>
>    I've designed and prototyped a circuit which controls high current
>outputs.  I'm feeding a low voltage source through a few power MOSFETs that
>pass up to 8 Amps max.  I'd like to get a few PCB printed, and am doing the
>CAD work myself (ORCAD).  However, I am concerned about how to handle these
>high currents with a printed circuit board..  What is the usual technique
>when high current is involved??? The MOSFETs are housed in a TO-220 package.
>Thanks in advance.
>
>-- Nick
>----------

Quick & Dirty OK?  Traces that are too thin for the current is the
first problem.  

	1. find out the copper thickness of the boards you might use
	2. multiply by first pass line widths of high current traces
	3. divide this cross sectional area into maximum current
	4. take this current density and compare to maximum current
		_density_ limits for copper wire derived from electrical
		codes, handbooks, etc. (max I / circ. cross sect area)
	5. if pcb current density is too big, increase linewidth or
		use thick copper clad.

I did something like this for a switcher I built.  A secondary
consideration (at least for switching P/S) is RFI from switching mondo
currents.  That gets more complex.

Jeff Gruszynski
T&M STE SE
Santa Clara Sales
Hewlett Packard
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