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1. 10:07 AM - Re: Flickering on PCA9685 PWM controller with 3W RGB LED (Paul Bryant)
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Subject: | Re: Flickering on PCA9685 PWM controller with 3W RGB |
LED
Chuoi,
I do know too much about electronics, but a good friend of mine is an electrical
engineer. I asked him if he had any ideas to help you. Here's what he said:
Tell him.
The way this works is to get the LED to "dim" your turning it on for 50 % of the
time. Real dim= the LED is on for 25% of the time. What I think is happening
is the 200 hz is too low for the DIM mode without flicker. Try 1000 hz. Using
a cap on the LED side is a bad idea but it might help (prob not) on the 12V
side. Also get a VHF handheld and scan the comm band for noise when you are
running this. It is possible for these PWM switches to put out a lot of noise
if not properly designed. You don't want to be dimming the lights to find
out you got no comm receiver anymore!
Mike Dwyer
-----Original Message-----
From: Chuoi <xiao46260@gmail.com>
Sent: Thu, Jan 12, 2017 3:34 am
Subject: Lightning-List: Flickering on PCA9685 PWM controller with 3W RGB LED
I'm hoping someone here has some experience with the PCA 9685 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.
PCA 9685 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.
here What am I doing wrong?
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=465002#465002
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