01-02-2016, 10:40 AM
If you wanted to be "belt and braces", you could add a series 10k resistor at the input of the gate, but after the catch diodes.
This limits the current that could flow in the intrinsic diodes should they have a lower Vf than the IN400x you've got (not impossible), and should they switch faster than the 1N400x (quite likely).
I've never looked up the current rating of the intrinsic diodes for regular 4000-series - I prefer not to rely on them for anything. On many ICs, specific ratings and guidance is given, but even so, it strikes me as dubious practice to include them as part of the circuit.
I'd probably use 1N4148 for the catch diodes (faster).
Good call on the VR37. I suppose a MOV between L and N might be worth considering if any doubt lingers...
At 50Hz, 1n looks like 3MΩ; 25M and 470k gives 6V peak, so you should be OK after a fair few cycles.
An easier way to control time constants might be to let the first gate ackle at 50Hz and use that to discharge a C - said C can charge in the absence of cycles, and can do so quicker if desired. That's the sort of thing that's needed for power-fail detect in audio amps, where you need to release the loudspeaker relay before any pops and clicks are heard. I usually just have a simple transistor (fed from a sniff of a secondary winding) to discharge the C every cycle...
Presumably the CMOS IC has Schmitt inputs
This limits the current that could flow in the intrinsic diodes should they have a lower Vf than the IN400x you've got (not impossible), and should they switch faster than the 1N400x (quite likely).
I've never looked up the current rating of the intrinsic diodes for regular 4000-series - I prefer not to rely on them for anything. On many ICs, specific ratings and guidance is given, but even so, it strikes me as dubious practice to include them as part of the circuit.
I'd probably use 1N4148 for the catch diodes (faster).
Good call on the VR37. I suppose a MOV between L and N might be worth considering if any doubt lingers...
At 50Hz, 1n looks like 3MΩ; 25M and 470k gives 6V peak, so you should be OK after a fair few cycles.
An easier way to control time constants might be to let the first gate ackle at 50Hz and use that to discharge a C - said C can charge in the absence of cycles, and can do so quicker if desired. That's the sort of thing that's needed for power-fail detect in audio amps, where you need to release the loudspeaker relay before any pops and clicks are heard. I usually just have a simple transistor (fed from a sniff of a secondary winding) to discharge the C every cycle...
Presumably the CMOS IC has Schmitt inputs
