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From: jfw@ksr.com (John F. Woods)
Newsgroups: sci.electronics
Subject: Re: NEGATIVE VOLTAGE?
Keywords: polarity
Message-ID: <2657@ksr.com>
Date: 13 Mar 91 15:55:19 GMT
References: <1991Mar8.140031.20095@uncecs.edu> <1991Mar8.182508.15573@zoo.toronto.edu> <4662@osc.COM>
Sender: news@ksr.com
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jgk@osc.COM (Joe Keane) writes:
>In article <1991Mar8.182508.15573@zoo.toronto.edu> henry@zoo.toronto.edu
>(Henry Spencer) writes:
>>I'm not sure why -12 is such a problem.  The circuits for negative supplies
>>are no more complex than those for positive supplies, and IC regulators are
>>just as available.
>Unfortunately, this last statement is not true.  For some reason, positive
>regulators are more common.  You can probably find what you want in a negative
>regulator, but you won't have as much of a choice.

Digikey has 79L12's, 79M12's, and 7912's.  In fact, their 79xx series has
almost as much variety as their 78xx regulators (I don't see a 79L09 or
79L10 to match the 78L09 and 78L10, but there are 79M{09,10} and 79{09,10}
models).  You won't find negative regulators surplus all that often, that
is true, but hey, Digikey has no minimum order and pretty reasonable prices,
too.