Keeping a high output LED safe from a peaky PS

[norwegian]

Hi friends!

Im having some trouble with LEDs getting destroyed when used on a fixed current PS.
The project involves the following parts:
10pcs CREE XP-G2 Q5
1pcs LED driver 40 W, MeanWell LCM-40 DA

The design involves the switching in and out of leds while power is on.
The leds is coupled in series, and there will be from 1 to 10 led powered.

My problem is that there seems to be some sort of voltage peak when switching the number of LEDs, resulting in destroyed LEDs.

Ive drawn a circuit which i think will solve the problem, and save my poor LEDs.
it consists of a zener and a resistor in in paralell with the LED.

Thanks, and i hope anybody can help a very novice student

 

[BradtheRad]

Do the led's flash brightly (too brightly) just before they go bad? This means the forward current became too great. Your zener-resistor arrangement will not necessarily help in that case.

Or if the led's are destroyed by reverse voltage, then you can install a single plain silicon diode, rated at a sufficiently high reverse voltage to protect the entire string.

These suggestions assume the driver is not malfunctioning, and that you are using it properly. However if it ruins led's, then it may not be functioning properly.

 

[FvM]

The power supply output raises to 110V when the load is disconnected. Apparently the stored energy in the filter capacitor is sufficien to damage the LEDs. You can conclude that the power supply apparently isn't suited for this kind of load switching.

A make-before-break switch which doesn't disconnect the load could probably solve the problem.

Looking at the LED I/V characteristic, I don't believe that the shown circuit can protect the LEDs. A series resistor and parallel zener diode would be a better idea, unfortunately causing an additional voltage drop and power dissipation. A series connected current limiter to 400 or 500 mA, that only activates during load switching and doesn't cause a voltage drop in normal operation would be the ultimate protection.

As a more simple solution, limiting the power supply output to e.g. 33V with a power zener diode will probably reduce the stored energy during switching to a level that can be handled by the LEDs.

 

[norwegian]

Thank you both for reply.

The LEDs dont flash brightly, but turns of and on for half a second when the number of leds attatched is changed, and when the number reach 4 they are destryed.

Ive drawn a circuit based on both of your replys.
Do you think this could be the solution?
Whould the values of the resistors work?

**broken link removed**