LEDs in O22s

First question I have is upon a visual inspection, is the actual LED burnt out, usually signified by a black dot on the die? If not, it likely is the accompanying driving circuitry failed and not the LED itself. Depending upon the LED manufacturing/design, it could be that they are intended for a nominal 12V operation and use in our nominal 18V environment is stressing them. With solid state items like this, the best thing to do is lower their temps and stresses by somewhat under driving them. Also, the solenoids of the switch machine can generate voltage spikes that the touted TVS diodes are to help suppress. Do you have TVS protections on your accessory circuit for these O22s?

@bmoran4 posted:

First question I have is upon a visual inspection, is the actual LED burnt out, usually signified by a black dot on the die? If not, it likely is the accompanying driving circuitry failed and not the LED itself. Depending upon the LED manufacturing/design, it could be that they are intended for a nominal 12V operation and use in our nominal 18V environment is stressing them. With solid state items like this, the best thing to do is lower their temps and stresses by somewhat under driving them. Also, the solenoids of the switch machine can generate voltage spikes that the touted TVS diodes are to help suppress. Do you have TVS protections on your accessory circuit for these O22s?

Good points, bmoran4, thank you! I have no TVS protection on my accessory circuit for the 022s. Will get that protection soon. Arnold

@Arnold D. Cribari posted:

Good points, bmoran4, thank you! I have no TVS protection on my accessory circuit for the 022s. Will get that protection soon. Arnold

Arnold,

I agree with what bmoran4 has said above. The below is a nice visual representation of how a typical LED works (Current on the y-axis, Voltage on the x-axis). Once the LED has exceeded the rated values, the p-n junction will breakdown and the LED will be destroyed.



Do you have a data sheet of the LEDs that you have purchased? It will state the maximum voltage and current that the LED can accept before it enters the breakdown region.

Bryce

I recall Arnold is using the drop in LEDs from Town and Country. I'm not aware they have published true data sheets or details on their driver circuitry. This is not a dig against T&C because I'm not aware of any other vendor that does either.

Another thing that will kill an LED is reverse voltage. Unlike most common rectifier diodes an LED has a low reverse voltage rating, maybe only 5 volts or so. When powering with AC you should have a diode in series with the LED to prevent the reverse voltage from damaging the LED. My guess is the ones you are using simply have a dropping resistor without the diode.

Pete