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From: panek@hp-and.HP.COM (Jon Panek)
Newsgroups: sci.electronics
Subject: Re: 12 to 9 volts dc
Message-ID: <13650002@hp-and.HP.COM>
Date: 12 Feb 91 16:03:30 GMT
References: <1991Feb10.220719.17078@cbnewsl.att.com>
Organization: HP Andover Division (Massachusetts)
Lines: 19

I'd have to agree...  my Toyota Celica voltage meter regularly floats around
15-16V while the engine's running.  A constant voltage drop setup, like the
in-line zener, or the chain of Si diodes is not a very robust solution.
The simple solution is the 7809.  Make sure the power rating on the '09 
is enough to handle the expected dissipation:  P = EI, where E is the
voltage *difference* between the engine (use 15-18V) and the output of
the device (9V) -- this gives E of ~9V.  I is the current
needed by the discman.  This gives you power in watts.  Note that devices
higher than about 0.5W require proper heat-sinking to achieve their max
ratings...

I sure wouldn't want to risk *my* discman on a junkbox solution...

Good luck!

Jonathan Panek
Hewlett-Packard, Andover Division
panek@hp-and.an.hp.com
(508) 687-1501