LED reverse breakdown voltage
LED reverse breakdown voltage
(OP)
Hello,
I'm wondering if anyone has any experience with subjecting an LED to a reverse voltage that is higher than its Vrbd.
The specific question would be this: How long before the LED would see catastrophic failure? Most LED datasheets that I've read specify a Vrbd of 5V. Hypothetically, if the LED was connected in series with a resistor and an 4VAC power source, and there was no reverse protection on the LED, then how long would it be before the LED failed? I specify 4VAC because at its peak, it would be just slightly higher than the Vrbd of 5 V.
Also, what generally happens to the forward voltage of an LED over time. Does it tend to decrease or increase? I have not found much discussion on these topics and was hoping someone had direct experience.
Thanks for any advice.
I'm wondering if anyone has any experience with subjecting an LED to a reverse voltage that is higher than its Vrbd.
The specific question would be this: How long before the LED would see catastrophic failure? Most LED datasheets that I've read specify a Vrbd of 5V. Hypothetically, if the LED was connected in series with a resistor and an 4VAC power source, and there was no reverse protection on the LED, then how long would it be before the LED failed? I specify 4VAC because at its peak, it would be just slightly higher than the Vrbd of 5 V.
Also, what generally happens to the forward voltage of an LED over time. Does it tend to decrease or increase? I have not found much discussion on these topics and was hoping someone had direct experience.
Thanks for any advice.





RE: LED reverse breakdown voltage
TTFN
RE: LED reverse breakdown voltage
If you are going to run AC to an LED you always put a diode in reverse across it(parallel). That way you will never subject it to more than ~1V backwards.
Use any old diode; 1N40xx or a 1N4148.
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: LED reverse breakdown voltage
My question about the forward voltage may have been a little unclear earlier. Let's forget about the AC example for a moment. Under normal operating conditions, does anyone know if Vf on an LED tends to increase, decrease, or stay the same?
RE: LED reverse breakdown voltage
So the actual diode's turn-on voltage probably does not change that much, but the amount of current drawn will continue to increase, until it's essentially impossible to turn on the diode itself, without running so much current as to destroy it anyway.
TTFN
RE: LED reverse breakdown voltage
Current screws with VF more than temperature.
Temperature screws with VF more then age.
And age will increase VF over a few thousand hours. On the order of 100-200mV.
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: LED reverse breakdown voltage
Dan - Owner

http://www.Hi-TecDesigns.com
RE: LED reverse breakdown voltage