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Triac Angle Detector and Dimming

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Full Member level 3
Aug 21, 2006
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triac angle detect

Can anyone give me a good reference for a Angle Detector, DImming Decoder and Controller for LED Driver? The only reference I have is the National Semiconductor DataSHeet which is **broken link removed** .

It is in figure 1 page 7 and the explanations are in page 10 and 11 respectively. I already finished my design for the constant current for LED. Now I need to study and design my own Angle Detect :(
Please Help. I need to finish my design till this November. I will tape out my IC layout soon ..

I'm assuming you're asking how to design this from the ground up.

There's two ways it's commonly done.

Professional way: (high power statcoms, active rectifers, inverters, etc) Use a PLL. It can be implemented in hardware or software and locks on to the line frequency.

Hobbyist way: (light dimmers, ...) Use an optocoupler to detect your zero-crossing point. Use software from there.

I'll assume you're going the hobbyist route.

So, get an AC optocoupler and connect it directly to the AC line (with limiting resistors, ofc). Hook the output to a microcontroller. You should see a '1' 99% of the time, with a small '0' spike when the line crosses 0.

Measure the time between pulses and use this as your base. Note that you do not need real units! For example, run a timer interrupt when you see a zero crossing and then interrupt again to stop it when you see another zero crossing. You should have caught either the positive or negative half of the waveform (doesn't matter). Say, for example, that your uC did 1000 timer ticks between 0-crossings. If you want to fire at 45 degrees (half power) you would reset the timer at every 0-crossing and fire the next time your timer reaches 500 ticks.

Hope that helped...

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