Solution for dimming an array of LEDs

[edaedaeda]

Ok,
I have designed a circuit using a current limiting capacitor in series, driving an array of leds. for 120VAC .47uF 200v cap. It seems to work pretty good. Now I would like to dimm the leds. How can I do this using a dimmer switch that is off the shelf. One way I am considering is by using a rheostat. Will this work?

Eda

 

[pranam77]

Re: ac LED project

Using a rheostat is a straight forward approach. It will surely work but may not that accurate as you expect it to be. Mean the dimming may not be in a linear fashion.

 

[edaedaeda]

Re: ac LED project

Thanks for the input pranam.
Here is another approach I am considering>>
Rectify current to DC. Once I do this I am wondering if it would be easier to use any type of dimmer. The important thing on this project is that any type of household dimmer switch will work with device. Whats your take on it?

Regards,
Eda

 

[pranam77]

Re: ac LED project

When your operating voltage across the LED's is above 30+, a rehostat is highly expected to get a good result. and if your voltage is below 30, you can use a variable regulator such as LM317 to drop it to required potential. This will work in a linear way. The dimmer switch used as fan regulator just works on chopping the waveform and may not work up to your expectation. Just put your circuit here so that i can get a clear picture instead of hunting in the dark. Hi hi...

 

[edaedaeda]

Re: ac LED project

pranam,
Thanks for the great feedback!
Here is the initial idea for rectified version. I will put the AC version up if you would like to see as well.

I need to be able to use the waveform chopping type of dimmer. (that is the most common type these days right?)
I am wondering if I can simply take a sample of the rectifed input voltage before it goes into regulator to adjust led driver. But this probably creates other problems.

Eda

 

[pranam77]

Re: ac LED project

Thatz nice. In your schematic, you get 24-30 volts rectified DC. Just feed this in to a LM317 which is a voltage regilator which will vary the regulated voltage from 1.2 to 27 volts. I think this is a simple and hazard free idea instead working on mains. An application example can be taken from the related doccument attached here.

 

[edaedaeda]

Re: ac LED project

Ok Pranam,
Here is a real simplified idea. Is there a way to adjust the output by sampling the input?

 

[edaedaeda]

Re: ac LED project

Ok Pran,
I promise to quit bugging you about this.
But here is another idea for adjusting output.

 

[pranam77]

Re: ac LED project

Thanks for the input. I think the last PDF i sent, is simpler than the ones what you have sent. Coz it will have only 3 resistors to control the output. Here in your circuits the base bias is adjusted to pull the AdJ pin of th regulator to ground. If you choose to use your design, i think it will also work but i strongly recomend a resistor say 100K from the base of the transistor to ground to keep the biasing stable in the first circuit. Ohh.. ok in the second circuit it is corrected. Go ahead. Good luck.

 

[edaedaeda]

Re: ac LED project

Pranam,
You rock!
Let me know if you ever need anything. I will keep you posted on outcome.

Eda

 

[edaedaeda]

Re: ac LED project

Hey Pranam,
By the way what does that mean? P.M. me if ya wanna tell.
Going back through the post trail I had promised AC version of Array.
Here it is in all its simplicity...

Eda