CFAG16080A-TMI-TZ pwm dimmed backlight flickering

[bfrigon]

Hi,

I use a pwm dimmer (PCA9530) to control the backlight on my CFAG16080A-TMI-TZ. There is flickering on the backlight when i set the duty cycle below 30% and it gets worst as it goes down. I can see the flickering even more if i look the lcd at an angle.

Since the PCA9530 outputs can't handle large currents, i used a NPN transistor (BST39) to switch the backlight.

The PCA9530 is located about 5 inch away from the transistor on an another board. It looks like there is jitter on the pwm signal. I don't know that for sure since i don't have an oscilloscope to test it.

What can i do to filter the signal?

Thank you

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[cosmicvoid]

What frequency is your PWM signal? You should probably use at least 200 Hz.

 

[bfrigon]

152Hz. This is the maximum frequency the PCA9530 can provide... nothing i can do about it...

If i understand correctly, the flickering is due to the lcd refreshing the display faster than the pwm signal causing a strobe light effect that allow me to see the "scan line"

This makes sense, because when i set the duty cycle to the lowest setting, i can actually see the "wave".

I'm going to try to find a faster PWM. but before i do so, is there something i can do to fix this?

 

[bfrigon]

I found the solution...

I can't make the pwm go faster, but i found a way to make the lcd to refresh slower. I set the LCD display duty to 98 instead of 80 and re-adjusted the contrast... It works great now.

Thanks CV.