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1) An LED is diode; right? So that it conducts in one direction only?

2) LEDs are normally operated by DC, from a DC supply or battery such as in an LED flashlight?

3) What happens if I apply AC? Keeping in mind that the AC will have peak voltage 1.4 times that of a DC supply the AC supply could be at a lower RMS voltage?

4) So, for example if the DC in item (2) was at 12 volts with suitable dropping resistor etc. the AC could be at around 8.5 volts RMS, right? But in the reverse or nonconducting state of the LED that would result in 12 volts peak (backwards) across the LED.

5) However if the reverse voltage was limited to to no more than the forward voltage of the LED would that be OK?

6) No particlar application at moment; just curious!

Reply to
terryS
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The LED is indeed a diode. The reverse peak voltage it can tolerate is not what a diode designed to rectify could handle. Depending on the LED there is no guaranty that limiting the revese to the forward voltage would be OK. So you could exceed the reverse peak of the LED and burn it out. Why don't you look at some specs of LEDs?

Tom

Reply to
Tom Biasi

If the AC is more tahn a few volts, you will blow the LED. The reverse allowed voltage is quite low, but one of the tricks for using AC is to use two LEDS parallel, but one of them in the reversed direction. Each will conduct for half a cycle, and protect the other LED.

Reply to
Sjouke Burry

Or just a normal diode in the reverse direction has the same effect.

John G.

Reply to
John G.

I think most LEDs will tolerate about 5 VDC in reverse, and probably will not blow out unless the current is not limited to the usual forward current. There are also LEDs with built-in antiparallel diodes, sometimes one red and one green, so if DC is applied it will tell you the polarity, and with AC it will light yellow.

Paul

Reply to
Paul E. Schoen

it conducts better in one direction, forcing it to conduct in the other direction will damage it.

yeah, continuous, or pulsed, DC is the norm.

the led will blink really fast :)

not good for many leds.

most LED datasheets quote 5V as maximum reverse voltage, and forwards voltage will be less than that, so yes that would be OK.

they make some 2-colour LEDs like that, with a red and a greed led in antiparallel, connected one way it lights red, the other way green, and with ac you get both red and green and the combination appears yellow,

Reply to
Jasen Betts
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I tried this 3 years ago and made a movie. Have a look:

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Reply to
bos

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