Do I need anything in the circuit to stop the flickering?

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Do I need anything in the circuit to stop the flickering?

Postby Ashleee » Wed Nov 15, 2017 10:22 am

I'm hoping someone here has some experience with the PCA9685 PWM controller (16 channel, I2c interface). So far everything is working pretty well after getting the circuit connected properly. I'm using a Picobuck LED driver to drive this high power RGB LED.

PCA9685 datasheet:

The PCA9685 allowed for a PWM frequency of between 40Hz and about 1500Hz. The default is 200Hz. After setting this frequency, I can choose the pulse on and pulse off interval anywhere from 0-4096 (which is the pulse resolution). So if I want the LED on full brightness, I can set On=0 and Off=4095. This works fine and I get a nice solid LED.

However if I start to dim one of the LEDs to say 25% of it's brightness, I'll set the On=0, Off=1000. This dims the LED but sometimes it starts to flicker. I've tried a lot of different combinations of On/Off times and PWM frequencies. Even at 1000Hz it is flickering, and it gets worse when I start to use all 3 RGB components.

I'm driving the Picobuck with a seperate 12V DC source, and it has a heatsink. Do I need a resistor or a capacitor somewhere in the circuit to stop the flickering? All I'm trying to do is get the LED dimmable from 0-100% without any flicker, so I can combine the red, green and blue colors.

Here is a picture of the setup, there are no extra components - just PCA9685 board, Picobuck and the RGB LED. The red/black wires off the Picobuck are going to a seperate 12V DC supply.

AuFSj.jpg (56.27 KiB) Viewed 2978 times

What am I doing wrong here?
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