# Led driver - constant current or constant voltage

I have an LED driver that ins't working. i have tried to search for the actual part, and been over to RS to find what I need.

There are two possibilities on RS - but I am not sure if I need the constant current or the constant voltage variety. ([two led drivers on RS])2

It is going to light two strips each with 36 leds in a mirror that was bought from bathstore - who don't seem to want to help.

What is the voltage of the driver output when connected to a strip? 12V
What are the values of the resistors? they have '241' printed in tiny letters.
How many resistors? 12 per strip
Are there 32 or 36 LEDs per strip? defo 36 strip (my bad!)
Are the strips wired to the driver in series or parallel?  I am not sure - the two strips are connected together via a 3mm jack plug/socket


What I would say is that the pictured LED driver did work for about 3 years. One day the main fuse box went (due to toaster). The LED mirror has never worked since. I have replaced the IR sensor - which now works.

RS is 'radio spares' a place to buy electrical components. The link shows two drivers that I thought might work????

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Full strip Close up

• In the end per LED you want constant current, but if they are equipped with current limiting resistors, you achieve that by applying constant voltage. We can't know. – PlasmaHH Apr 13 '18 at 14:25
• thanks Would it be possible to tell if I posted a photo of the led strips - there is nothing on them that looks like a resistor (well to me anyway) – maxelcat Apr 13 '18 at 14:48
• Your current draw per LED might be as much as 20-30 mA per lamp, so 20 mA/LED * 32 LEDs = 640 mA, which is greater than the supply can handle, which may be why it failed. A picture would be good. – schadjo Apr 13 '18 at 14:49
• added a couple of pictures of the LED strips – maxelcat Apr 13 '18 at 16:31
• Is that a picture of the not-working driver? I would indicate it's a constant current device with no dimming capability whatsoever? – Barleyman Apr 13 '18 at 16:42

Your driver has an output of 416 mA @ 12V and is constant current (CC).

You need to know the voltage input to the LED strip.

Based on this picture it appears there is one current limiting resistor for each three LEDS. What make this more difficult is, in the photo, the ends of the strips are cut off, you say there are 32 LEDs, and the PCB says 36 LED. Three LEDs per resistor makes more sense if there are 36 LEDs (12 resistors) than 32 (10.666 resistors). I cannot see how the strips are wired.

The five needed unknowns

1. What is the voltage of the driver output when connected to a strip?
2. What are the values of the resistors?
3. How many resistors?
4. Are there 32 or 36 LEDs per strip?
5. Are the strips wired to the driver in series or parallel?

I am going to assume the power supply should be 12V constant voltage. Although a CC driver may (or may not, depends on the value of the resistors) work with one strip. If the strips are wired in series, the pictured driver would not work becasue you would then need 24V.

If the driver does not light up one strip by itself then I would guess the board needs more than 416 mA. 5 watts seems to be very inadequate for even one strip with 36 LEDs. They appear to be high power LEDs like a Cree Xlamp with a 350 mA test current. So the strip may be trying to draw more the 416 mA which drops the driver voltage below 12V and the LEDs do not have enough voltage to light up.

I do not know what RS means.

## UPDATE

The 241 on the resistor mean 24 x 101 or 240Ω
So the current flowing through each resistor is about 37 mA Which means the 3 LEDs and resistor = 444 mW
.444 W x 36 resistors = 5.328 W x 2 strips = 10.656 W

You need a plain old power supply, not an LED driver.
Power Supply Needed: 12VDC out and at least 1 Amp or 12 Watts.
RS 12V Power supplies