# Power LED module and finding the correct resistor...

#### Ftwist

Joined May 14, 2019
2
Hello All,

I have what must be a very simple problem but I'm struggling to get my head around it.

I have these TruOpto OSPR6XW5-W4XZE1E1E White 6500K 6x1W Power LED 600lm and I am running each module of a 12v 3a DC power supply however I feel as though my working out is wrong while calculating the value of the resistor I need to use in the circuit for current limiting purposes.
So I am hoping you will be able to help me and show me where I am going wrong!

So...

R = (Vs - Vf) / If
Resistance = (Source Svoltage - Forward Voltage) / Current
Fill with info from the datasheet:

R = (12v - 10v) / 0.35
R = 5.7

Am I shooting in the right direction?
There is no mention of 'Forward Voltage' on the Datasheet so I have used the typical operating voltage.

Then I presume I have to work out a Power rating for the Resistor once I have the correct resistance value?

#### Ftwist

Joined May 14, 2019
2
Bump?

#### ericgibbs

Joined Jan 29, 2010
9,528
hi Ftwist,
E

#### djsfantasi

Joined Apr 11, 2010
6,121
Hello All,

I have what must be a very simple problem but I'm struggling to get my head around it.

I have these TruOpto OSPR6XW5-W4XZE1E1E White 6500K 6x1W Power LED 600lm and I am running each module of a 12v 3a DC power supply however I feel as though my working out is wrong while calculating the value of the resistor I need to use in the circuit for current limiting purposes.
So I am hoping you will be able to help me and show me where I am going wrong!

So...

R = (Vs - Vf) / If
Resistance = (Source Svoltage - Forward Voltage) / Current
Fill with info from the datasheet:

R = (12v - 10v) / 0.35
R = 5.7

Am I shooting in the right direction?
There is no mention of 'Forward Voltage' on the Datasheet so I have used the typical operating voltage.

Then I presume I have to work out a Power rating for the Resistor once I have the correct resistance value?

Where did you get these values? Particularly If and Vf? I see you explained how you picked 10V for Vf, but why?

Re: power rating, yes, you do! How are you going to do that?

#### LesJones

Joined Jan 8, 2017
2,493
Post a schematic of how the 6 LEDs are wired to the power supply. (You will probably have to trace the etch on the PCB.)

Les

#### Jony130

Joined Feb 17, 2009
5,145
Looking at the PCB photo it seems to me that your LED's are arranged this way:

Can you confirm it?