Re: LED at 60 HZ? (was RE: Radio Shack Strobes)

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: Jerry Chamkis <jchamkis-at-bga-dot-com> 

It's true- an LED will work fine.  Regular LEDs turn on and off plenty fast
for this application but there might be some question about -some- white LEDs
that use a UV-excited phosphor.

Two things to keep in mind though-

1.  You must protect the LED from reverse voltage.  You can either put a diode
in series or a diode in parallel facing the opposite way of the LED.

2.  You must limit the current through the LED so a series resistor is also
required.  You may get away with powering it directly from a (very) small
transformer because it can't supply a huge amount of current, but that LED
won't die of old age!  You can probably get away with 50 - 100 ma peak
current through a full-size LED and of course it's perfectly acceptable to
use multiple LEDs for increased brightness.

Jerry

On Tuesday 24 February 2004 02:10 pm, Tesla list wrote:
 > Original poster: "Daniel Kline" <daniel_kline-at-med.unc.edu>
 >
 > An engineering friend says a high-brightness LED on a
 > low-voltage transformer, like 6 Volts, connected through
 > a suitable resistance, should flash at 60Hz in sync with
 > the 60Hz mains. (50Hz for you all over there :)
 > It seems too easy to me...he thinks that the LED may have
 > a "persistence" issue. In other words, just because it
 > turns off quickly doesn't mean it stops emitting quickly.
 > Comments?
 > Thanks,
 > Dan K

-- 
Jerry Chamkis
jchamkis-at-bga-dot-com