Adv LED-64 voltage setting recommenations

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azamia12
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Adv LED-64 voltage setting recommenations

Postby azamia12 » Sun May 18, 2014 9:35 am

Hello,

I am planning on using the following LED's 3609_0 - 5mm Four Chip Super Flux White with
1032_0 - PhidgetLED-64 Advanced. I will eventually use all 64 outputs.

My question is the 3609 is rated at 3.0-3.2 VF, what should I set the anode voltage on PhidgetLED-64? Mid that I want to achieve maximum safe brightness from these LED's.

Currently I am running at 2.75V, 20ma, 100%

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Patrick
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Re: Adv LED-64 voltage setting recommenations

Postby Patrick » Tue May 20, 2014 9:30 am

Have a look at the LED Primer: http://www.phidgets.com/docs/LED_Primer ... e_Settings

You should drive your LEDs at 3.9V, or you won't get their full brightness. The extra voltage is just converted into heat on the 1032, it doesn't affect the LED.

-Patrick

aro
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Re: Adv LED-64 voltage setting recommenations

Postby aro » Thu Jul 17, 2014 6:01 pm

I have a similar question, but for a different LED. The datasheet that I have says the Max Fwd Voltage is 3.6V.

Do you mean that the board will sense the maximum voltage and not apply more than that (dissipating it as heat)? How does the board know how much heat to dissipate to not max out the LED?

Or do I need to just add a resistor to bring the voltage down from the closest level (3.9V) to either the max (3.6V) or the typical level (3.3V) listed on the datasheet?

Thanks!

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Re: Adv LED-64 voltage setting recommenations

Postby erik » Fri Jul 18, 2014 9:04 am

It's not so much as the LED-64 sensing the amount of voltage being applied to the LED, but the amount of current going through the LED (to control the brightness). You can think of it as the LED-64 internally setting a resistor to a value in order to achieve the desired current so that you do not need to add an additional one.



The Forward Voltage of an LED corresponds to the amount of voltage that needs to be applied in order for the LED to turn on. You can use any voltage to power an LED as long as it is higher than that voltage and as long as you choose a resistor that limits the current through the LED below its maximum rated current.

The min, typical and max Forward Voltage ratings that are listed in datasheets mean that the Vf can vary from LED to LED. On average, a random LED with that part number will have a Vf of around 3.3V, but some LEDs can have a Vf as high as 3.6V. This means that when you have an LED attached through a 220 Ohm resistor, the same LED part numbers can have some slight variations in brightness.

aro
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Re: Adv LED-64 voltage setting recommenations

Postby aro » Fri Jul 18, 2014 12:37 pm

Ah, so if I understand right given the manufacturing variability, the highest minimum voltage (or highest voltage needed to turn the LED on) I would need would be 3.6 V, so the 3.9 V setting would be fine to cover all manufacturing variability in the LEDs.

Thus, I don't need a resistor with the LED-64 and can just set it to 3.9V and 20mA (which is the max recommended current).


Thanks for the clarification.


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