LED backward breakdown voltage and LED as a indicator lamp

[SemiconductorCat]

>> https://robot.lk/viewtopic.php?f=19&t=2725



I never done this partially, but I heard that LED's can't afford large reverse voltages, like more than 3-5V.
Is this circuit is stable?

I think indicator lamps are special kind of LED which engineered to handle large reverse voltages. I seriously
have no expertise in this. I need more research to be done. Any idea ? But wikipedia also told that they
have very low avalanche breakdown voltages.

if you know more info on this subject please share.


thanks in advance

[Neo]

Note that the circuit in that link is forward biased, not reverse biased. So this is nothing to do with that circuit.

However as you said, when a LED is reverse biased (connected in the wrong direction) there is a reverse breakdown voltage (avalanche) defined as for any semiconductor with a PN junction. This is marked as PIV (peak inverse voltage) in datasheets. The PIV of a LED is very low indeed. And since the supply impedance to LEDs is inevitably very low, a heavy enough current can damage the LED.

In such cases where reverse voltage is possible on an LED, it is a common practice to use a diode together as well to stop the reverse current flow through the LED.

[SemiconductorCat]

if I brought a local LED, which datasheet that I should refer.

I understand this, there's no point of killing a whole datasheet just to a indicator lamp.
But my father want everything very neet.

Which diode you suggest? What kind of considerations I should take into account when
selecting that diode?

from my basic things that I studied in university I could only figure out how to calculate it's min
peak breakdown voltage , which is root(2)*230 V.

What about other parameters? Such as recovery time?

and another problem , there's a shaded pole motor connected to same power rails. And the person who
shout on me does not used any device called 'soft starter' , and that motor is generating very bad 3rd harmonics.
,Never mind,but I need also to think about that rude environment around that LED.Any suggestions on this?

[SevenZero]

Hahhh.. Semiconductor... after a long long time.

if I brought a local LED, which datasheet that I should refer.

You need to get it from the seller as there is no other way to find which LED type you are buying. Basically it comes as a set of parameters, not as a datasheet. If you are looking for LEDs with datasheets, better try Cree. If the seller doesn't agree with you to provide even those parameters in minimum, then there is no option for you.

Which diode you suggest? What kind of considerations I should take into account when selecting that diode?

A diode which stops passing any reverse current except in extreme conditions. IN4001 could be enough. Refer to specs of both LED and Diode to comply with that minimum requirement.

For the last question.. it seems like you are referring to avoiding back EMF which can reverse bias the LED. This can be avoided by installing another diode in the opposite direction to the motor.

[Rksk]

Another easy solution here,
Just get two LEDs and connect their opposite sides (like paralle).

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