Is a zener in parallel with the LED required?

[fabiodl]

Reading this datasheet for the VLMU1610-365-135 uv LED, I stumbled upon the wiring diagram on page 4. Why is there a zener diode in parallel with the led? Should I really place a protection (?) diode in parallel with each LED? isn't a curent limiting resistor sufficient?

[Zero999]

The LED already has a built-in diode, so there's no need to add one. It's there to provide protection against reverse polarity, which can easily damage InGaN LEDs, especially the more exotic UV types, which are more delicate. A series resistor will suffice.

I don't know why it's a zener, rather than an ordinary diode, since the LED is bound to turn on first. Perhaps it's faster than the LED, so will absorb high current ESD, before it gets to the LED?

[rpiloverbd]

I think they suggested adding the Zener diode for reverse polarity protection.

[Zero999]

I think they suggested adding the Zener diode for reverse polarity protection.

Where does it say that?  I couldn't find anything about adding an external zener diode.

The internal schematic shows a zener diode is built-in

Reverse voltage ⁽¹⁾    I_R = 10 μA    V_R  1.2 V

⁽¹⁾ Reverse  current  is  applied  for  reverse  voltage  test  only  (function test  of  Zener  diode). The device  is not designed  for  reverse  operation. 
     Operating the LED under reverse current condition for long time might result in damage or failure of the component

Also refer to figure 7.

[nigeltron]

A zener may be placed in parallel to pass current to other leds that it may be in series with if the led fails.
Also, it has some use in esd protection.
Also, there are "led protectors" that you can buy to do the same thing as the zener...onsemi make them...

here is one...
https://uk.rs-online.com/web/p/tvs-diodes/7737891p?cm_mmc=UK-PLA-DS3A-_-google-_-CSS_UK_EN_Semiconductors_Whoop-_-TVS+Diodes_Whoop-_-7737891P&matchtype=&pla-806308433405&gclid=EAIaIQobChMI74nRu8jX9QIVSuztCh29_gA3EAQYAiABEgJopfD_BwE&gclsrc=aw.ds

NUD4700SNT1G

[Zero999]

A zener may be placed in parallel to pass current to other leds that it may be in series with if the led fails.
Also, it has some use in esd protection.
Also, there are "led protectors" that you can buy to do the same thing as the zener...onsemi make them...

here is one...
https://uk.rs-online.com/web/p/tvs-diodes/7737891p?cm_mmc=UK-PLA-DS3A-_-google-_-CSS_UK_EN_Semiconductors_Whoop-_-TVS+Diodes_Whoop-_-7737891P&matchtype=&pla-806308433405&gclid=EAIaIQobChMI74nRu8jX9QIVSuztCh29_gA3EAQYAiABEgJopfD_BwE&gclsrc=aw.ds

NUD4700SNT1G

That's a good idea, but it's not a zener diode. It's a crowbar circuit, consisting of an SCR and most likely a zener diode in series with the gate. It has a high impedance, as the voltage across is is increased up to around 5.5V to 7.5V, then the impedance drastically falls to the point, when there's roughly 1V across it, irrespective of the current. The idea is so a string of LEDs will not all turn off, just because one of them fails open circuit.