PCA8685 16CH 12Bit Shield and LED Current

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ELNewb
 
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PCA8685 16CH 12Bit Shield and LED Current

Post by ELNewb »

I am trying to utilize the PCA9685 PWM Shield to drive multiple strings of LED fairy lights. I have 3.3V at VCC because that is the logic level from the microcontroller. The board works well when wired like in the datasheet but as noted only supplies about 10ma to the LED. I would like to drive around 20ma and noted the PCA9685 should be able to sink up to 25ma but I cannot figure out the correct wiring. Applying >5v to the V+ line (on a common ground to VCC) and sinking through the board works but anything over 5.5V and I am unable to turn the LED completely off. I have tried various configurations of MODE2 on the PCA9685 chip to no avail.

I assumed if the LED string has a forward voltage of 2.5V, I should be able to press 7.5V or so through V+ without issue and get a max of 23ma to the LED (7.5V-2.5V/220=.023) and limit the voltage to the chip to <5.5V on its pin (due to the voltage drop from the LED) but I suspect I am not comprehending something about how this works. Should I be able to pass 20ma through this board or are the 220 ohm resistors limiting the ability?

Thanks!

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adafruit_support_bill
 
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Re: PCA8685 16CH 12Bit Shield and LED Current

Post by adafruit_support_bill »

The PWM/Servo shield is optimized for driving servos. The 220 ohm series resistors will limit the current available for driving LEDs.

The TLC59711 is a better match for what you are trying to do: https://www.adafruit.com/product/1429

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