I don't think anyone has said it, but dimming a halogen lamp is not a good idea. Halogens need to operate a full power to produce the heat necessary to maintain the halogen cycle. Lower power will darken the glass and shorten the lamps life.

Very good point! I had completely forgotten about that.

 

Why can't use a chip 6N139M + resistor at 200 kilohms? Can take a double chip, then it will be clear whether the positive or negative half-wave. Or am I wrong?

 

That's three times that circuit has been recommended. Do we have a quorum?

Make that four times.

 

I tried to simulate a circuit with a 6N136. The error is approximately 500 microseconds.

I also checked the diagram from message #19. It turns out a little better.


It remains to collect these schemes and look under load.

 

if you switch ON the triac at 0V terminal ... it does not remain ON -- you must hold it until the "forward" current increases enough
about https://www.st.com/resource/en/appl...an-important-parameter-stmicroelectronics.pdf

 

Made the Board from post # 19. Suitable for controlling thyristors.