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what is a freq/duty to pwm a LED?

 
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Nick
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what is a freq/duty to pwm a LED?
PostPosted: Fri Sep 03, 2004 10:04 am     Reply with quote
Just looking for a place to start. I wish I has a scope right now. I have a 1mhz clock.

Nick
newguy



Joined: 24 Jun 2004
Posts: 1907

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PostPosted: Fri Sep 03, 2004 10:23 am     Reply with quote
Not sure what your question is about. Are you asking how fast you should PWM an LED so that you can control its' brightness without any visible flicker?

If that is what you're asking, then you should pulse it faster than about 100 Hz. Most people can see the flicker up to about 20 Hz, but some people can see fluourescent lights flicker (that's 120 Hz).

Experiment and see for yourself.
Nick
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PostPosted: Fri Sep 03, 2004 10:50 am     Reply with quote
I want save current with the PWM, so I really dont care if it flickers at all. No matter what freq/duty I put it on, I still use .9 ma.

Nick
SherpaDoug



Joined: 07 Sep 2003
Posts: 1640
Location: Cape Cod Mass USA

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PostPosted: Fri Sep 03, 2004 12:40 pm     Reply with quote
The average light produced is proportional to the average current. PWM allows you to vary brightness by adjusting duty cycle, but for a given brightness it does not save any average current. If you use the PWM to drive a buck type switching supply you may save some current at the cost of some components.
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