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From: whit@milton.u.washington.edu (John Whitmore)
Newsgroups: sci.electronics
Subject: Re: 12v dc -> 9v ac converter
Message-ID: <16555@milton.u.washington.edu>
Date: 17 Feb 91 00:16:40 GMT
References: <91043.135514UD186413@NDSUVM1.BITNET>
Organization: University of Washington, Seattle
Lines: 29

In article <91043.135514UD186413@NDSUVM1.BITNET> UD186413@NDSUVM1.BITNET (Space Studies Student Organization) writes:
>I'm interested in building a converter that would allow me to run a
>Commodore VIC 20 computer from a 12v motorcycle battery.  The
>computer needs a 9v ac input.  Is it possible to synthisize this
>easily?  The current load is less then 3 amps max. 

	There were two slightly different VIC-20 designs; one used
an external 5V/3A power supply and had 9VAC input only for some low-power
internal uses (like the RF modulator).  The earlier VIC-20's had
only an external transformer, and only 9VAC input (2-pin power socket).

	If yours is the recent design (DIN multipin power plug), you
can just regulate your +12V externally to +5, and try a '555 at 1 kHz
with a moderate size coupling capacitor (20 to 50 uF) to make it
AC for the 9VAC pin.  It'll be marginal, but probably will work.
	If yours is the older design, consider taking out
the old power transistor, and connecting a 5V regulator from the
battery (or use a 6V battery and one diode to get it to about 5V).
Again, a couple of places need the AC, but you can do that with
a '555 (or do without; does a robot really need the TV output?)
	The VIC uses that 9VAC to generate +5 and some +12, but
you'd have an easier time not trying to make AC; the VIC only needs
it to get some DC power, so give it the DC and forget the AC.

	The 'VIC Programmer's Reference Manual' has a foldout
schematic in the back, which will be well worth perusing.
My copy is at home, or I'd be more specific.

	John Whitmore