Re: Regulated 9 Volt DC Power Supply

On Fri, 28 Dec 2007 04:51:04 -0800 (PST), "Dave.H"
<the1930s@xxxxxxxxxxxxxx> wrote:

On Dec 28, 11:39 pm, John Fields <jfie...@xxxxxxxxxxxxxxxxxxxxx>
wrote:
On Fri, 28 Dec 2007 02:38:02 -0800 (PST), "Dave.H"

<the19...@xxxxxxxxxxxxxx> wrote:
Can anyone help me with information on building a 9 volt regulated
power supply that runs off 250 volts AC mains? Any help greatly
appreciated.

---
How much current?

--
JF

I'm not exactly sure. The radio uses 6 "D" cells. I'm not sure of the
current rating of "D" cells.

The Energizer E95 (D cell) data*** uses 10 ohms as the load for a
radio example. Assuming that is correct, you are talking about
(6x1.5V/10) or almost an amp load. But I'm sure that volume affects
this, too. Anyway, using that as a reference I guess that a solid 1A
or 1.5A supply would probably cover the need. Of course, that could
indeed vary a lot from radio to radio, so of course more is better.

Problem is, you can expect transformers delivering much more than an
amp on their secondary, at voltages enough higher than 9V to be useful
in linear circuits, to be expensive/big. You may be able to measure
your current draw, with an ammeter if you have one. But my guess is
that a largish wall wart supply should be okay for your use. I think
you can get to around the 1A to 1.5A you are probably looking at.

By the way, D cells are rated to operate over a range of current
loads. They are usually selected over C or AA, not quite so much
because they last longer (they do) but more because they are capable
of larger current draws without serious loss of lifetime. This
suggests that your radio really does want access to something in the
100's of milliamps rather than something in the 10's. So you really
do need to figure on estimating about .5-1A or so, simply because it
uses D cells.

Jon
.