PWM flicker fix - add resistor to lower LED brightness

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sadbuttrue

Gawd
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Feb 16, 2008
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Most LED monitors need to be run at quite a low brightness to prevent blindness. Unfortunately this is where PWM becomes a major problem. If one placed a resistor before the LEDs, you could take the brightness down to such a level that 100% brightness on the display would be acceptable for every day use. This would remove all PWM flicker. If in a few thousand hours the display started to dim slightly due to age (LED has a long half-life so not a big issue), you could simply replace the resistor/s.

Anyone DIY proficient enough willing to try or at least detail how easy this is to do?
 
What about some sort of variable resistor with a knob sticking out the back of the lcd?
 
Druneau said:
What about some sort of variable resistor with a knob sticking out the back of the lcd?
Click to expand...

What you're describing is a potentiometer.

I don't know much about these PWM implementations but for an LED display you would want to use a current limiting resistor. I imagine it will get quite hot.
 
LEDs need a certain amount of minimum voltage to work.
So using a resistor/poti will likely not lower the brightness enough before the LED goes dark.

A better way is simply using a PWM dimmer that doesn't suck.
I've got a 2500hz dimmer that I've been wanting to put inside my Catleap for quite some time already.
But unfortunately I don't know the exact voltage they need and can't risk damaging my main work monitor atm.
 
You cant dim like that. LEDs need to current controlled not voltage controlled. Usually by a LED driver circuit. The upside is that LED drivers all support direct current control without PWM:
http://powerelectronics.com/lightin...nalog-dimming-any-led-driver-0112/index1.html

So its very possible. Problem is that its kind of a bitch to deal with factory made PCBs and such for hobbyists. An electronics professional could very easily and cheaply do it with the right equipment, though.
 
A simple low brightness/high brightness switch then? Heck, call it eco-mode and market to the green crowd.
 
The real fix would just be for monitor makers to use higher switching frequencies. I cannot understand why they are so low. Electronic ballasts for CFLs like you get in the store generally switch at 20-30kHz for efficiency reasons. If they had a similarly fast PWM circuit for the monitor LED backlights, there'd be no issue, it would be well beyond human perception. Also there wouldn't be any worry about it emitting noise, since it would be ultrasonic if it did.
 
or maybe they should just supply a working lcd with no backlight and let us hang it on the window to work in natural light. lol
 
Sycraft said:
The real fix would just be for monitor makers to use higher switching frequencies. I cannot understand why they are so low. Electronic ballasts for CFLs like you get in the store generally switch at 20-30kHz for efficiency reasons. If they had a similarly fast PWM circuit for the monitor LED backlights, there'd be no issue, it would be well beyond human perception. Also there wouldn't be any worry about it emitting noise, since it would be ultrasonic if it did.
Click to expand...

There would always be people that complained that it flickered, even at those frequencies!
 
Sycraft said:
The real fix would just be for monitor makers to use higher switching frequencies. I cannot understand why they are so low. Electronic ballasts for CFLs like you get in the store generally switch at 20-30kHz for efficiency reasons. If they had a similarly fast PWM circuit for the monitor LED backlights, there'd be no issue, it would be well beyond human perception. Also there wouldn't be any worry about it emitting noise, since it would be ultrasonic if it did.
Click to expand...

well, audio noise

the weak signal enthusiast ham operator next door might not be so enthusiastic
 
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