Hello,

We are wanting to do high frequency PWM dimming of the output of current transformers (which feed LED lamps) hooked up to a twisted pair bus.
Do you think the “gap toothy” resulting waveform (see below) will be a cause of any problems?

(This is a different question on a subject discussed elsewhere here)

Block diagram………………..

….you can see the “shorting FETs which dim by stopping current flowing to the LEDs when the FETs are ON.

We do NOT want to do low frequency PWM dimming, (~200Hz) because the low frequency of this dimming causes problems for the current source. (-it means the current source is switching from high power to low power output which causes problems)

Therefore, we wish to do dimming at a much higher frequency (83.3KHz). But do you think that the resulting current waveform (as below, when D is not equal to 1) is going to mean problems?


LED lamp current with no dimming (D = 1)

LED lamp current with dimming with D = 0.083
http://i48.tinypic.com/3ctas.jpg


LED lamp current with dimming with D = 0.33

LED lamp current with dimming with D = 0.92

(Also, how would you reduce dissipation in the current source by correcting the power factor in the twisted pair?)

 

Do you think the “gap toothy” resulting waveform (see below) will be a cause of any problems?

I don't think it'll be a problem. We'll see if someone else has a different idea.

 

Thanks, sorry, i got my rectifiers the wrong way round in the above block diagram....

..it should be

Block Diagram
http://i46.tinypic.com/28151kz.jpg


Sorry in the first post , i said "current transformers".....theyre actually "Resonant Inductive Couplers"
http://en.wikipedia.org/wiki/Resonant_inductive_coupling

...please ignore the number of secondary turns....its actually a resonant inductove coupler.