# Leveraging DC series circuit to power higher voltage LED panel

I have a IKEA RGB Dioder set where each channel requires 12Vdc (& 1.25W), I want to connect this to my Phidget LED 64 Advanced.

Each channel on the Phidget can provide a maximum of 5Vdc with 80mA, from what I understand I need a resistor in the series to connect three 3 channels to provide sufficient voltage for one LED panel? What type of resistor will I need?

EDIT: I'm currently using what @clabacchio suggested where 7.5Vdc is provided by one transformer and the Phidget bumps up the rest. Only the Red LED cannot achieve perfect on/off switching but I should be able to mitigate this via stepping down all Red LEDs

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If I understand correctly you would connect 3 output of the board in series to stack voltages? –  clabacchio Mar 6 '12 at 12:26
Because I couldn't get a series to work off linking 2 channels on the Phidget (the voltage was still around 5V), I decided to try a secondary power supply that provides 7.5V and then use the Phidget controller to make up the rest. –  Callum Jones Mar 6 '12 at 14:01
Of course it was! The channels are most likely ground referenced, and is not clear how did you "link" the two. One way could be to use the outputs as active low, connecting the LED between the 15V supply and the positive pin of the signal; but you have only a 5V swing and you won't obtain a perfect on/off switching –  clabacchio Mar 6 '12 at 14:03
Hey clabacchio, I tried linking them via series circuit. I'm currently using what you suggested where 7.5Vdc is provided by one transformer and the Phidget bumps up the rest. Only the Red LED cannot achieve perfect on/off switching but I should be able to mitigate this via stepping down all Red LEDs. –  Callum Jones Mar 6 '12 at 14:23

Fortunately, the Phidget seems capable of using an external power supply of up to 15V. They say

• Externally Supplied Current Consumption (max) VDC = 15V

It seems you can probably use an external 12V supply and no resistor with the Phidget doing the current control BUT you should talk to a dealer or the user commuinity who MUST have done this before.

Just possibly:

12V, 1.25 W. I = 1.25/12 ~= 0.104A

Use 15V and LEDs are 12V so.
R = (Vsupply-Vled)/Iled = (15-12)/.104 =~ 29 ohms.
27 ohm std E12 value probably OK. Use 0.5 Watt or higher.

BUT see dealer or user community.

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Thanks Russel! I've added some info in the OP. –  Callum Jones Mar 6 '12 at 14:24
@clabacchio Done! –  Callum Jones Mar 6 '12 at 15:17
@CallumJones seen! –  clabacchio Mar 6 '12 at 15:32