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I have a large array of LEDs that I need to be true to their datasheet light frequency emission (ex 635 nm.) The LEDs require Vtyp @ 20 mA ranging from 2.2 V to 1.2 V. Some are within 0.1 V of each other.

In the interest of minimizing the number of Zener power circuits I need to add, could I put both a 1.8 V and 1.9 V on a 1.8 V power source without much light frequency deviation? Any way to know how much or guess the direction of the deviation?

I just remember from past experience that over-volting orange LEDs color-shifted them to yellow. I never knew if this was a bandgap/voltage thing or just overheating LED caused it.

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Use a ready made LED driver. Based on the number of LEDs and current needed, you can choose drivers available. An example is this from analog devices.

enter image description here

Depending n type of power supply you have, you can narrow down to a suitable LED driver.

You can also build a constant current driver using one opamp and a transistor. I can suggest.

Wavelength vs Temperature Graph

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  • \$\begingroup\$ Yeah that would probably be the right way to do it, but as an ME I will spend all day finding a driver that supports 20mA and another day figuring out surface mount adapters ;-) I will probably go with the resistor method since variance in intensity is not as big of issue as variance in frequency, and based on the info you guys provided there shouldnt be any issue with frequency deviation as long as I dont overheat the LED. Thanks for the wavelength vs temperature graph, that is super helpful! \$\endgroup\$
    – ericnutsch
    Jan 24 '20 at 20:57
  • \$\begingroup\$ Hope you don't mind that I added a printscreen of the Added wavelength vs temperature graph to your answer. Might be helpful for future readers if the spreadsheet disappears in the future. Thanks again! \$\endgroup\$
    – ericnutsch
    Jan 24 '20 at 21:10
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You need to control the LED current, and let the LED choose its own voltage.

Typically, you use a constant voltage power supply somewhat higher than the highest forward voltage of the LEDs you are using. Add a resistor in series with each LED to limit its current to its typical value - generally somewhat less than the Absolute Maximum current listed in the datasheet.

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  • \$\begingroup\$ Hmmm, I didn't think about it like that. I always thought of resistors as a crude way of doing it. So I guess I could calculate each resistor with R=(Vs - Vtyp)/20mA. Or maybe putting them all in series and getting a constant current power supply would be the better route... With that knowledge though I guess my past overvolting experience must have just been overheating the semiconductor. Thanks for your super fast and clear reply! \$\endgroup\$
    – ericnutsch
    Jan 24 '20 at 7:41

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