# Multiple Different Voltage LED's

Discussion in 'The Projects Forum' started by MrWuTangDragon, Jun 30, 2015.

1. ### MrWuTangDragon Thread Starter New Member

Jun 30, 2015
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Hello all! I have been working on custom gamecube controllers for a while now and i have just started experimenting with LEDs. I want to run three LED's (different colored) to the rumble motor on the controller. These LED's are red, green, and yellow with forward voltage of 1.9-2V, 2.9-3.1V, and 1.9-2V respectively. The power supply for the rumble motor is 5V according to online resources that I believe is credible. What I am having trouble with is distributing the power efficiently with minimal wiring, for there is not much space in the controller. I've been looking into parallel/series hybrid circuits. My thought was somehow parallel the red and yellow because they have the same Vf and series the green to even it out to approx 5V therefore I would not need a resistor. Any ideas are welcome!

2. ### Bordodynov Well-Known Member

May 20, 2015
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Bad idea to include diodes do not contain resistors. You need to know that the forward voltage of the LED depends on the temperature. Including two successive diode to 5 volts you can lose them. You need to use three resistors of approximately 150 Ohms - 1k. By changing the resistor you can adjust the brightness of the LED. You can connect LEDs in parallel if the actual forward voltage does not differ more than 10-30 mV (at the same current). Otherwise, the LED current will be very different.

Last edited: Jul 2, 2015
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3. ### #12 Expert

Nov 30, 2010
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With a 5 volt supply, the minimum resistance is:
150 ohms for a 2 volt LED
100 ohms for a 3 volt LED
for (2) 2 volt LEDs in series, 50 ohms.
These numbers will put the LEDs at 100% of their rated current.
Hint: There is no rule that you must run LEDs a the highest current they will survive.
For an indicator you will be looking right at, you might even run them at 1/2 to 1/4 their max. Just multiply the resistance by 2X to 4X what I said above.

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4. ### MrWuTangDragon Thread Starter New Member

Jun 30, 2015
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First off thank you for the help. I tried wiring the red and yellow LEDs together and the green parallel and gave appropriate resistors to each LED but now only the green lights up. I only have 200 ohm resistors but I'm pretty sure I can make the appropriate resistance via wiring the resistors in parallel and series. I might have messed up the resistors but i tried many different combinations at for some reason I cant get the red and yellow to light up.

5. ### #12 Expert

Nov 30, 2010
17,887
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Reality intrudes. Either you broke one of them, or one of them is backwards, or they aren't really 2 volt LEDs, or your power supply isn't good for 5 volts under load, or something like that. Because you are not the kind of person that has a dozen drawers full of resistors, just use (3) of your resistors, one in series with each LED, and be done with it.

6. ### KeepItSimpleStupid Well-Known Member

Mar 4, 2014
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with your 3.1 V LEDS, the most you can have with a 5 V supply is 1. 3.1*2=6.2 and you used up all of your voltage.

Your resistor would be something like (Vsupply-(Sum of all of the Max Vf's))/(operating current)
e.g.R<=( 5-3.1)/20E-3 A 3.1 V LED on a 5 V supply operating at 20 mA

7. ### ian field AAC Fanatic!

Oct 27, 2012
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When you have LEDs with different voltages, there is a trick that can save you a wire or two.

If you have a red LED at about 1.8V and a green at 2V, wire them both to a common current limiting resistor - you can rig it so the green LED is on by default, but if a transistor switches the red into parallel with the green, the red lower Vf clamps the voltage to less than the green needs and the green goes out.

AFAICR: each colour has a slightly different Vf, so you may be able to expand it to more than 2 LEDs - but I haven't tried it.

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8. ### MrWuTangDragon Thread Starter New Member

Jun 30, 2015
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I checked to see if they were broken or backwards and they weren't. Is there an easy way to test whether or not they are truly 2 volt LEDs or if the power supply is good for 5 volts under load?

9. ### MrWuTangDragon Thread Starter New Member

Jun 30, 2015
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I wired the red and yellow separately now and still they wont light even a little bit. I will now post a picture so you guys can do a better analysis. Also in the picture there are only 3 200 ohm resistors but initially i tried using 4 in parallel to get a resistor value of 50 ohms and i also tried 5 resistors for 40 ohms, but nothing worked. The green LED is on the right and it lights up fine. The one on the far right is the red and middle is yellow but neither seem to work. I looked it up on the sight i bought them and they say all the LEDs are approx 20mA.

10. ### MrWuTangDragon Thread Starter New Member

Jun 30, 2015
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Also there is not much space in the controller for that many separate wires. I rather not use more if I have to.

11. ### #12 Expert

Nov 30, 2010
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Place 1 resistor in series with one LED. Do that three times. When you get done, you can measure the voltage across each LED to find out what its real voltage requirement is.

Do not use the instructions for [2 LEDs in series] for a reason to place 4 resistors in parallel and feed all that current to [one LED]. Throwing triple or quadruple the recommended current through an LED tends to burn it out.

12. ### ian field AAC Fanatic!

Oct 27, 2012
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To get real serious about making those measurements, a constant current source would ensure comparing all the different LEDs on the same basis. 20mA is probably as good a starting point as any.

The TS shouldn't have any great difficulty finding simple current limit circuits online, you can also use a JFET just by shorting gate to source - there are JFETs with Idss that high, but most have quite a tolerance spread - as long as the current it limits is the same every time, that's all that's needed.