[Elecraft] Building a power supply

Wed Dec 18 06:15:01 2002

Julian,

Your 2 x 9V windings in series into a a bridge rectifier (two diode
drops) and a fat input capacitor say 4700uF is going to present the
regulator with about 24V --- if you are shooting for 13.8V there is
more than enough head room for the regulator which will need some heat
sinking.
The LM388K regulator (+3-35V @ 5A) looks like a good choice but a bit
pricey, the alternative would be an LM317 type with a pass transistor.

Bill Scovell / VK2SOE
----- Original Message -----
From: "Julian (G4ILO)" <[email protected]>
To: "Elecraft List" <[email protected]>
Sent: Wednesday, December 18, 2002 8:03 AM
Subject: [Elecraft] Building a power supply

> I'm just about getting round to building the power supply for my K2
into
> the EC2 enclosure I bought a long time ago, when I discovered that
the
> transformer I was thinking of using is a few millimetres too tall.
This
> transformer has a single output winding which measures about 17V,
which
> would have been fine as I'm going to be using a bridge rectifier.
>
> I'm looking at a toroidal transformer to fit into the EC2 case but
I'm not
> quite sure what I need, as the ones I can buy all have *twin*
secondary
> windings. Should I get one described as 2 x 9V and connect the two
> secondaries in series? Looking on the web for guidance the only
power
> supply circuit diagram I found showed two secondaries connected in
parallel
> which seems to me (perhaps wrongly) as not the best thing to do. If
the
> windings weren't exactly matched you'd get current flowing from one
into
> the other, wouldn't you? If it is possible to use paralleled
secondaries,
> can I go for a current rating half what I want?
>
> Also, is the magnetic field greater or less with a toroidal
transformer?
> The VFO of the FT-817 I had used to "warble" when sat on top of its
power
> supply, because of this.
>
> The transformer supplier's web page is at
> http://www.antrimtransformers.com/80VA.htm.
>
> Thanks in advance for any help.
> --
> Julian, G4ILO. (K2 #392)
> Homepage: http://www.qsl.net/g4ilo
>
>
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