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

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

Original poster: Terry Fritz <teslalist-at-twfpowerelectronics-dot-com>

Hi,

You can't use just straight AC since the sine wave voltage will spear the 
image.  You need very fast bright "short pulses" to freeze an object's 
motion.  Here is a simple circuit for an LED strobe that works ok.

http://hot-streamer-dot-com/TeslaCoils/Misc/STROBE.ZIP

Cheers,

         Terry


At 01:46 PM 2/24/2004, you wrote:
>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