[ILUG] OT: stepping down from 12v to 9v
junk_mail at iol.ie
Mon May 1 20:58:46 IST 2006
On Tue, 2006-05-02 at 15:15 -0300, Snowbat wrote:
> On Thursday 27 April 2006 20:32, Brendan Kehoe wrote:
> > We've got a tiny Ethernet
> > switch that wants 9V, but a 230->13.6V transformer, who has two contacts
> > (+13.6V, and a ground). A junction box feeds one device, a WRAP board,
> > that wants 12V. But the switch wants 9V.
> It may want 9V but you may well find the 9V supply goes directly to an
> internal 7805 and the whole device runs off the 5V output from the 7805, in
> which case you can run it on anything from 7.5V to 28V. That's the case with
> an old 8 port hub I have here.
> 9V is perfect for feeding a 7805 but it's an 'odd' voltage for a switch to run
> on directly, so worth checking.
Is this still going around?
7809s are rare & old. They standardised on 7805, 7808. Get the 7808, put
approx 500 ohms (some) or 1K (the rest) in the GROUND pin and you have
9V. A capacitor (1 - 10uF) would be nice on the output, to prevent
oscillation. Use the TO220 variety
With Best Regards,
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