Re: 12V regulator

On Tue, 21 Oct 2008 01:03:42 -0400, "Paul E. Schoen"
<pstech@xxxxxxxxx> wrote:


"Rich Grise" <rich@xxxxxxxxxxx> wrote in message
news:pan.2008.10.20.23.37.10.447840@xxxxxxxxxxxxxx
On Mon, 20 Oct 2008 17:17:10 -0500, Steve wrote:
On Mon, 20 Oct 2008 19:18:16 GMT, Rich Grise <rich@xxxxxxxxxxx> wrote:
On Mon, 20 Oct 2008 01:59:51 -0400, Paul E. Schoen wrote:
"Steve" <s@xxx> wrote in message
...
led switch, but it's proving a bit more difficult than I wanted for
this particular application. Thanks for the replies,
Steve

You should be able to use about a 10k resistor (about 1-2 watt), and a
1N4004 or higher rated diode, in series with the LED.

It's not necessary to put a diode in series - the LED is alreaady a
diode.
But it _is_ necessary to put a diode in antiparallel with the LED so its
reverse voltage stays belos its limit.

But the OP has already said that he doesn't have access to the resistor/
LED junction, so he's just going to spring for the neon switch.

So, would putting the diode in reverse across the switch terminals not
provide enough protection for the LED? Thanks for all the help,

Now that you mention it, yes - the other diode will clamp the voltage
across the resistor/LED series circut, which will serve the same
function as only clamping the LED - i.e., very limited reverse
voltage.

And don't forget the series resistor! :-)

I suggested the series diode so that the circuit will only conduct during
positive half-cycles, and thus reduce power and heating in the series
resistor. The reverse current through the diode should be low enough to
avoid damage to the LED when the circuit is reverse biased. A diode across
the LED will conduct during the negative half-cycles and just waste power.
You could use a bridge rectifier and a higher value resistor, but that adds
more complexity.

It's a good idea to use a fusible type resistor that is rated for line
voltage use, and the entire circuit should be well insulated and protected
from human contact or damage. The neon lamp is the best, but that means
getting a new switch or making major changes in the existing one. And you
can't get a blue neon lamp. You're stuck with red or yellow (except for
special green lamps).

Paul


Actually just use store bought LED illuminated switches.

.

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