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Help with 16-channel 12-bit PWM downlights prosject

by Thastian on Wed Jul 04, 2012 6:24 pm

Hey.
I have a huge cool project going on. Going to have my whole appartment fitted with LED downlights, and im planning to controlling(dimming) all of the downlights invidually. Have gotten a lot of help from another on another forum, but now im stuck at a problem. First the facts, then the problem.

Facts:
63902d1336042531-help-transistors-pwm-led-prosject-6w-led-driver.gif
Schematics
63902d1336042531-help-transistors-pwm-led-prosject-6w-led-driver.gif (11.13 KiB) Viewed 1988 times

Driver: 320mA, 3W, about 9v-10v
Ardurino Uno. and the PCA9685 on the schematics are the Adafruit 16-Channel 12-bit PWM/Servo Driver

problem:
When i set the frequency of dimming to 500Hz and start dimming, the driver makes a loud buzzing sound. but only when its dimming or not at max or mix. if setPWM is 0 or 4096 its quiet. What is making this sound. Tryed fitting a capasitator between the positive and ground on the driver output, but did not help. The sound gets louder the higher frequency i set on, but the LED is starting to flash/flicker under 200Hz.
I also did not have this problem when i tryed dimming the LED with PWM directly from Ardurino.

Very gratefull for all help.

For refrence the old forum thread on the other forum that helped me with the procject is here: http://www.electro-tech-online.com/elec ... sject.html
Thastian
 
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Re: Help with 16-channel 12-bit PWM downlights prosject

by adafruit_support_bill on Thu Jul 05, 2012 4:45 am

Is the sound coming from the PWM/Servo Driver, or the MOSFETs that are switching the LED current?
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Re: Help with 16-channel 12-bit PWM downlights prosject

by Thastian on Thu Jul 05, 2012 6:36 am

The sound is comming from the LED driver, not the MOSFET
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Re: Help with 16-channel 12-bit PWM downlights prosject

by adafruit_support_bill on Thu Jul 05, 2012 6:58 am

Can you post a diagram showing how you have everything connected?
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Re: Help with 16-channel 12-bit PWM downlights prosject

by Thastian on Thu Jul 05, 2012 7:34 am

Like this? =
downlightoppsett.png
downlightoppsett.png (565.5 KiB) Viewed 1961 times
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Re: Help with 16-channel 12-bit PWM downlights prosject

by adafruit_support_bill on Thu Jul 05, 2012 8:03 am

Some vibration in a PWM driver is expected. I suspect that the PWM switching frequency or one of its harmonics is exciting some resonance on the board. Often these resonances can be controlled by mounting the board to something solid and/or damping the enclosure with foam tape or other lossy material.
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Re: Help with 16-channel 12-bit PWM downlights prosject

by Thastian on Thu Jul 05, 2012 8:06 am

Okey. So its not "dangerus"?
But why dident this accur when i controlled the pwm directly from the Arduino board?

Thanks for the help =)
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Re: Help with 16-channel 12-bit PWM downlights prosject

by adafruit_support_bill on Thu Jul 05, 2012 8:10 am

No. It is not dangerous.
But why dident this accur when i controlled the pwm directly from the Arduino board?

On the Arduino, the PWM signal is generated by a more massive chip mounted to a more massive board. It will have a different (probably much lower) resonant frequency.
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Re: Help with 16-channel 12-bit PWM downlights prosject

by MEC Group on Thu Aug 09, 2012 9:23 pm

Nice project you got there. Down lights are really good especially on the banned and bathroom, My electrician in Melbourne told me that.
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Re: Help with 16-channel 12-bit PWM downlights prosject

by bboyes on Mon Sep 17, 2012 2:23 pm

What controls the current through the LEDs?

If your "driver" module in your diagram is a constant-current source LED driver, it may not be designed to be PWM-ed. Check its data sheet.

Bruce
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Re: Help with 16-channel 12-bit PWM downlights prosject

by gamer boy on Thu Sep 20, 2012 2:15 am

Nice thread... very nice information.....

Thastian wrote:Hey.
I have a huge cool project going on. Going to have my whole appartment fitted with LED downlights, and im planning to controlling(dimming) all of the downlights invidually. Have gotten a lot of help from another on another forum, but now im stuck at a problem. First the facts, then the problem.

Facts:
63902d1336042531-help-transistors-pwm-led-prosject-6w-led-driver.gif

Driver: 320mA, 3W, about 9v-10v
Ardurino Uno. and the PCA9685 on the schematics are the Adafruit 16-Channel 12-bit PWM/Servo Driver

problem:
When i set the frequency of dimming to 500Hz and start dimming, the driver makes a loud buzzing sound. but only when its dimming or not at max or mix. if setPWM is 0 or 4096 its quiet. What is making this sound. Tryed fitting a capasitator between the positive and ground on the driver output, but did not help. The sound gets louder the higher frequency i set on, but the LED is starting to flash/flicker under 200Hz.
I also did not have this problem when i tryed dimming the LED with PWM directly from Ardurino.

Very gratefull for all help.

For refrence the old forum thread on the other forum that helped me with the procject is here: http://www.electro-tech-online.com/elec ... sject.html
gamer boy
 
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