[ILUG] OT: stepping down from 12v to 9v

[Kenn Humborg]

> This is very OT, but I don't know of other lists that might be as useful
> for this sort of thing. :)
> 
> We're trying to find an easy way to convert a 12v DC current to 9V DC
> for a community wireless broadband scheme.  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.
> 
> I found that a 3.1V zener diode would do the job, but a) I've found no
> one in Ireland who sells them, and b) it would require a bit of a
> hardware hack to put it together which doesn't feel like it'd be the
> safest approach.

You'd get them from Farnell or Radionics or Maplin.  But they're
not the right solution.  Zeners are meant for very low-power
applications, or for generating reference voltage level for a
bigger regulator.

> 
> Anyone know of a device already available that would take a 12V DC
> signal (like comes in a car's 12V adapter) and step it easily 
> down to 9V DC?

You want something like a 7809 voltage regulator strapped to a
decent heatsink (the old-fashioned way) or a DC/DC converter.
Radionics/Farnell/Maplin might be able to help you out.  Call
them and ask to speak to technical sales support and tell them
what you want to do.  Alternatively, get your hands on their
catalogues and look for DC/DC converters.

Maplin is a bit DIY, so they might only be able to sell you
the components, while Radionics/Farnell may have a pre-built
product for you.

BTW, a DC/DC converter is just a 3 or 4-wire component and
doesn't generate much heat, so, depending on your soldering
skills, it might be feasible to put something together 
yourself.  

Later,
Kenn