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# Trouble out putting a DC current to AC current? Answered

Im looking for a way to use a 9v DC current to regulate an AC current.  I have a set up a diagram of my problem:

I thought of using a relay but i would like the light to be able to dim not just either be on or off, then i thought of a transistor but im not sure if that will work with both ac and dc at the same time.  I could really use some help here.

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## 14 Replies

keeperrico (author)2011-02-10

I think i found the circuit im going to try and breadboard and go from there:
https://www.instructables.com/file/FCF9N53GJQEE4MC/

Questions or comments appreciated.  Thank you everyone for helping me out I truly appreciate it!

steveastrouk (author)2011-02-07

This is one of those things that if you have to ask the question, you won't understand the answer.

I'm really not sure what the point of that circuit is for what you want to do. why does it have a window comparator in it ? Where's the cicrcuit from ? It will drive a load in 8 steps of brightness for some reason.

keeperrico (author)2011-02-08

the circuit filters audio signals into specific frequency bands and then compares the voltages from the input to convert from a logarithmic function to a linear function so the lights will no be dim the entire time and then all of a sudden be really bright.
here is the same exact circuit using nixie tubes:
but instead of nixie tubes i want to be able to use regular lights!

Trust me just because i ask a question does not mean that i can not understand the answer. I asked this to get input from the community not to be flamed for asking a legitimate question

steveastrouk (author)2011-02-09

This circuit isn't the way to do it, with AC. I'm not sure I see how the anti-log function is generated, if you say its there. The traditional method usually involves using the transfer function of a BJT as a feedback element.

So, here is a main powered formula:

Take your mains sinewave, stick it through a transformer, and generate, say a 6V sine wave.

Stick that through a comparator, and clip the sine wave into a nice square wave.

Stick that into an integrator, and turn the mains-locked square wave into a mains locked sawtooth.

Stick THAT into another comparator, but this time compare it to your audio signal, possible from your previous circuit (just take the signal from that last opamp, before the transistor)

Take THAT and put it into something like a MOC3020 opto-isolated triac driver (I've guessed at the number: I'm warm, but I suspect without research that the 3020 is a ZVC part, you DON'T want ZVC)

Use the output of the 3020 to drive a nice fat triac to drive your AC lights.

Make sure you put adequate snubbing and filters for the AC, phase control is inherently noisy.

And although that all sounds complex, it should fit on a quad op-amp, or two - you don't need a very fast "comparator", so an op-amp will work fine.

Scaling will need to be adjusted by experiment.

Steve

Jack A Lopez (author)2011-02-07

I think I know what you want.  I think the thing  you want is a DC voltage controlled dimmer switch.  For some time I have wanted the same thing.  I have not yet got around to building one.

I'm pretty sure I've never seen anything like it on the shelves at Walmart(tm), and this makes perfect sense because most of the zombies roaming the aisles wouldn't want one, unless somebody told them to want one.  In that case, they'd have trouble keeping them in stock.

The closest thing I ever found to a clue, to a plan, as to how to build such a contrivance, was on page 20 of this document:
http://www.littelfuse.com/data/en/Product_Catalogs/PowerThyristorApplicationNotes.pdf

It shows how to drive the gate on your thyristor using a PIC(tm) microcontroller,and that might not be all that useful to you if you don't know microcontrollers. I don't. Not really. There might be some good stuff on the preceding pages... maybe back to page 15.  There are bunch of circuits on these pages, and maybe some clues here.

Of course as sort of a prerequisite to understanding all that junk, it'll help if you actually know how a lamp dimmer works. Um, here:

http://home.howstuffworks.com/dimmer-switch.htm
http://mysite.du.edu/~etuttle/electron/elect5.htm

keeperrico (author)2011-02-08

Thank you very much you have been the most helpful so far!

Re-design (author)2011-02-07

Use a relay to turn the light on and off.

keeperrico (author)2011-02-07

I do not wish for the light to either be on or off, I would like it to be able to be able to dim, not just be either on of off.

kelseymh (author)2011-02-07

Then buy a dimmer knob. The problem you've posed is incomplete.

ARJOON (author)2011-02-07

well stated as i did.

kelseymh (author)2011-02-07

Yep :-) I think we may have overlapped -- your answer is dated "9:00 am", mine is "9:05 am".

keeperrico (author)2011-02-07

the complete schematic is here: https://www.instructables.com/files/orig/FX3/YJZS/FXHJXRX0/FX3YJZSFXHJXRX0.png

But instead of using a 125 DC Circuit to power the nixie tubes (the far right of the schematic) , i would like a way to use an AC light strip(like christmas lights) to pulse, dim, flash to the music from the circuitry.

Re-design (author)2011-02-07

Power it with d/c then you can use a dimmer circuti. Google "dimmer circuit" to find those.

You "may" be able to find a d/c controlled a/c dimmer but that's going to be harder and if you don't know much about working with 120 a/c it's dangerous.

ARJOON (author)2011-02-07

use a relay like re's said. and add a dimmer to it. why do you want to do it with dc.just install a light dimmer or you want to go to some timing systems?