26-06-2015, 01:23 PM
Looks really good 
I've done similar things in the past, but "discretely" with an MOC3049 opto-coupler driving the gate of a triac directly. The MOC3049 takes care of the zero-crossing switching, and is dead cheap. At the time, I was stuck for space and couldn't find an SSR that was small enough, but the S202S02 would probably have done the job if I'd discovered it (was it around in 2004, or did I just fail to notice it?). The MOC3049 has gone obsolete since then, but there are many suitable equivalents...
I think I'd want to add a resistor feeding into the diode in the SSR. Yes, there might be a penalty in voltage drop terms (might need a 4th diode), but that poor LED is a slave to the Vf drops of D1, 2, 3 and 5. Can you predict exactly what the LED current would be in all circumstances? Not sure I could
Doing so would allow you to use a smaller capacitor, as its TC is currently set by the slope resistance of the LED (guess a few 10s of ohms), and because there is no "padding", the capacitor only has to discharge very slightly between charging pulses before it goes out (which is no-doubt why it ended up being so large in value).
Just 100 ohms or so might make the difference - the voltage dropped would swamp the variations in the Vf of the various diodes and the LED itself.
In the past, I've idly considered using a current transformer for this. Passively achieving the required sensitivity while still dealing with the highest current could be challenging, to say the least, but it might be a fun project
I've done similar things in the past, but "discretely" with an MOC3049 opto-coupler driving the gate of a triac directly. The MOC3049 takes care of the zero-crossing switching, and is dead cheap. At the time, I was stuck for space and couldn't find an SSR that was small enough, but the S202S02 would probably have done the job if I'd discovered it (was it around in 2004, or did I just fail to notice it?). The MOC3049 has gone obsolete since then, but there are many suitable equivalents...
I think I'd want to add a resistor feeding into the diode in the SSR. Yes, there might be a penalty in voltage drop terms (might need a 4th diode), but that poor LED is a slave to the Vf drops of D1, 2, 3 and 5. Can you predict exactly what the LED current would be in all circumstances? Not sure I could
Doing so would allow you to use a smaller capacitor, as its TC is currently set by the slope resistance of the LED (guess a few 10s of ohms), and because there is no "padding", the capacitor only has to discharge very slightly between charging pulses before it goes out (which is no-doubt why it ended up being so large in value).
Just 100 ohms or so might make the difference - the voltage dropped would swamp the variations in the Vf of the various diodes and the LED itself.
In the past, I've idly considered using a current transformer for this. Passively achieving the required sensitivity while still dealing with the highest current could be challenging, to say the least, but it might be a fun project
