wallwarts and regulation..

John Speth johns at oei.com
Thu Mar 5 22:56:33 CET 1998

Or another way is to use a 7805 regulator with an as-close-to-8V zener diode (REVERSE biased - opposite from the 1N914 Jay recommends).

Does anybody know if using a zener like this introduces noise?

John Speth
Object Engineering, Inc.
johns at oei.com

-----Original Message-----
From:	Jay Martin [SMTP:jmar at intface.com]
Sent:	Thursday, March 05, 1998 1:31 PM
To:	'media at mail1.nai.net'
Cc:	'synth-diy at mailhost.bpa.nl'; 'cyborg0 at GlobalEyes.net'
Subject:	RE: wallwarts and regulation..

Better solution would be to use a 7805 with a diode forward biased in
the ground connection.  Should give you 12.7v with decent ripple
rejection (with the proper cap's off course)  I doubt that the .3v will
give you a problem.  If it ABSOLUTELY has to be 13v you could add a very
small trimpot to the ground or add 2 diodes forward biased..one silcon
(1N914) and a Germanium diode (germaniums have about a .3v forward bias
drop and silicon have about .7v).  Something like this:

IN -------7812------OUT

Again the diode would be FORWARD biased,,not REVERSED.  We are not
trying to block voltage, just trying to cause a slight voltage drop.
And don't forget filtering.  If you want me to CAD up a sample
schematic..let me know and I'll whip something up.

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