High Frequency PWM dimming of LEDs is OK?

[Flyback]

Hello,

We are wanting to do high frequency PWM dimming of the output of Resonant Inductive Couplers (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, needing a new thread due to new diagramatic info here)

Block diagram………………..
https://i46.tinypic.com/28151kz.jpg

….you can see the “shorting FETs which dim by stopping current flowing to the LEDs when the FETs are ON.
(-please ignore the number of secondary turns....as you know, there is a resonant coupling method)

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)
https://i47.tinypic.com/o9iv.jpg


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


LED lamp current with dimming with D = 0.33
https://i50.tinypic.com/1zofdzp.jpg

LED lamp current with dimming with D = 0.92
https://i49.tinypic.com/np5d91.jpg


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


Resonant inductive coupling…………
https://en.wikipedia.org/wiki/Resonant_inductive_coupling

 

[ronv]

I think you have to answer the last question first. What is the voltage and current in the primary?

 

[Flyback]

In the actual system the current in the primary is fixed 2.9 Amps AC 50KHz sinusoidal

 

[ronv]

If I understand correctly the primary is a single wire. If so what is the voltage of the primary and what is the load on it?

 

[Flyback]

the theory behind the couplers is "resonant inductive coupling"

https://en.wikipedia.org/wiki/Resonant_inductive_coupling

 

[ronv]

Maybe, but the frequency is wrong - see your other thread. It would help to know the answer to post 4. Perhaps it is just a single wire driven from a current source?

 

[Flyback]

Perhaps it is just a single wire driven from a current source?

This is the basic situation..but please ignore the detail of the turns in the coupler......this is where the top secret stuff comes into it.

https://i46.tinypic.com/28151kz.jpg


...As you say, it is pretty much a single wire driven by a current source