Dead LED's

[KRe8ive]

I have a circuit with 4 3w LEDs in series. There is a Voltage regulator on the + end with an incoming voltage of 24v. The voltage regulator appeared to be dead so i replaced it. The LEDs still do not work. Is it possible that when the voltage regulator died (win tested it had 24v on the output) it has killed the LED's? Is there an easy way to test if the LED's are ok?

 

[donkey]

there is an easy way to test the power supply, if it works then assume at least one led is blown.
the only way i can think of to test the leds is grab a battery pack, resistor, and test each one individually.

 

[(*steve*)]

Is there a resistor in series with the LEDs? If not, they may have expired due to excessive current.

Or is it a current regulator?

 

[KRe8ive]

It is a Variable Voltage Regulator, all the resistors are still ok on it. there is no resistor immediately in series with the LEDs... but very possibly further down the line. I have not looked that far down the line yet. Although I suspect there is not as on the -ve side i think it goes directly to what looks like a mosfett.

I didn't think of using a battery to test individual LED,s will give that a go, and see what I find.

Cheers guys

 

[junlee]

there is an easy way to test the power supply, if it works then assume at least one led is blown.
the only way i can think of to test the leds is grab a battery pack, resistor, and test each one individually.

I agree with this view.

 

[KRe8ive]

Hi Guys, Thanks for your help, checked it with a battery and indeed 1 LED in the circuit was dead, swapped it out and all working fine now.

 

[(*steve*)]

You may suffer the same fate again if the LEDs are being driven from a voltage source.

If it's a variable voltage regulator, then it *may* be set up as a current source. If this is so, your LEDs should be safer in the long term.

(Considering that a current regulator requires fewer parts than a voltage regulator if using a common three terminal regulator, I would hope it's a current regulator!)

If it's a three terminal regulator (like an LM317) and the circuit has a single (generally low value) resistor, it's a current regulator. If there are 2 resistors (generally one will be between 220 ohms and 560 ohms, than the other, some number of kOhms) then it's a voltage regulator.

If it supplies more than just the LEDs it is also more likely to be a voltage regulator.

 

[KRe8ive]

You may suffer the same fate again if the LEDs are being driven from a voltage source.

If it's a variable voltage regulator, then it *may* be set up as a current source. If this is so, your LEDs should be safer in the long term.

(Considering that a current regulator requires fewer parts than a voltage regulator if using a common three terminal regulator, I would hope it's a current regulator!)

If it's a three terminal regulator (like an LM317) and the circuit has a single (generally low value) resistor, it's a current regulator. If there are 2 resistors (generally one will be between 220 ohms and 560 ohms, than the other, some number of kOhms) then it's a voltage regulator.

If it supplies more than just the LEDs it is also more likely to be a voltage regulator.

It is an LM317M, With 2x Resistors, Have not got it infront of me so cannot give more specific details. There is what looks like a mosfett down the line on the -ve side of the LEDs. Chinese made Item made very poorly, these are keeping me occupied with constant repairs. (in total is 24 LEDs on 1 Heat Sink). there is a fan for cooling, with a sleeve Bearing, they are al giving out pretty quickly, we have 22 of them (well 20 now that I have used 2 for parts). Oh well, am learning lots playing with them