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Topic: Did I kill the LEDs with an incorrect resistor position ? (Read 1 time) previous topic - next topic

DaveO

I recently read that in a series string of LEDs, it doesn't matter if the resistor is on the Vcc or Ground side.

My ( self appointed ) logic deduced from this was that the resistor just had to be in the string somewhere.

I have 15 LEDs, split into 5 series strings of 3 LEDs each.

Vf = 3.2v
Current = 20mA
Source = 12.43vDC

I am using a 150ohm resistor per set of 3 LEDs.

Due to the layout of the wiring connecting the LEDs, I chose to position the resistor on the Vcc line between the 2nd and 3rd LEDs.
On power up, the first 2 light for a second, then die.

Did I have the resistor in the incorrect position ?  Does the resistor position matter ?

oops, just realised, I have the 3 LEDs in each string connected in parrallel ( 3 Vcc connected, and 3 Gnd connected, with the resistor on the Vcc line of the 3rd LED. )

I guess that's why they died a spectacular dead as the magic smoke was seen escaping.

Would still like to know about the resistor position once I correct the wiring to 'in series'.

So is this correct :
Vcc ..... LED+ .. LED- .. LED+ .. LED- .... R150 .... LED+ .. LED- .... Ground

or MUST it be either :
Vcc .... R150 .... LED+ .. LED- .. LED+ .. LED- .. LED+ .. LED- .... Ground
or
Vcc ..... LED+ .. LED- .. LED+ .. LED- .. LED+ .. LED- .... R150 .... Ground


RuggedCircuits

You are correct in that the position of the resistor in a series connection of LED's doesn't matter. Your parallel connection of LED's does explain why two of them died.

--
The Ruggeduino: compatible with Arduino UNO, 24V operation, all I/O's fused and protected

DaveO

Thanks RuggedCircuits

I'll put this experience down to "School Fees".

Just glad it wasn't something with my Arduino Mega connected to it.

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