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Trouble finding non-schottky SMD power diode

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magic:
So you have a wire which is part of some mains circuit carrying up to 10A and you want to detect when it conducts at least 10mA?
And you are absolutely sure that no other power supply can be made available? So where is the output signal going?
Do you realize that you cannot connect the output to ground as drawn, or to any other fixed potential for that matter?

MustardMan:
Yes, correct. Detect 10mA or above, up to 10A. No external power supply available.

The output could best thought of as an LED in an opto that indicates the circuit is active. In reality it is a little more complex than just an LED.

The only reason a ground is shown on my posted circuit is because Microcap requires it to perform a simulation: there is no (and will be no) actual ground reference.

I did not think of it till now, but you have made me think 'current transformer', and using its' output to drive "the LED". 1000:1 though, I would have to think about a core that could give me enough output at 10mA but not go up in smoke at 10A, or produce so much output at 10A that it would make clamping it down to something usable worse (dissipate more power) than the diode idea.

Cheers, MM.

EDIT: I don't like playing with mains, so I am leaning pretty heavy on the simulation at present. When it gets real I will be working with 24 volts (AC) to do real world tests... as long as my voltage is above the drop of the "diode sensor", the actual voltage should not be of much importance, only the current. Final stage, after *all* verification, mains connection.

mikeselectricstuff:

--- Quote from: MustardMan on August 20, 2020, 10:26:59 am ---
I did not think of it till now, but you have made me think 'current transformer', and using its' output to drive "the LED". 1000:1 though, I would have to think about a core that could give me enough output at 10mA but not go up in smoke at 10A, or produce so much output at 10A that it would make clamping it down to something usable worse (dissipate more power) than the diode idea.


--- End quote ---
If you can get a CT to detect at 10mA without too much primary dissipation, then that may be a good choice - chances are the core will just saturate at higher currents, which shouldn't be a problem.
The challenge is to get enough voltage - current is less of an issue as you can use a micropower pulsing circuit if necessary to drive LED/Opto etc. if all you want is to detect on/off state, i.e. charge up a capacitor until you have enough energy to pulse the LED.

MustardMan:
I am currently following two investigative paths...

First: Looking at datasheets for different TO220 diodes. None yet with a curve that looks as good as the S10AL, but I am rather dubious about that particular datasheet anyway so I have a few from digikey on their way.

Second: Dismantling a commercial RCD. Since they are sensitive to an imbalance of 30mA (or better) and can trip a solenoid at that sensitivity, and handle significant overload (more than 10A), I could run one deliberately unbalanced (one core wire) and see what comes out of it.

Both methods involve current detection, so I can easily get away with 24 volts and not have to play with mains. Whew!

I have not looked much at RCDs except out of interest. From the little I've seen, it is unclear if they output  a high voltage/low current to trigger the solenoid, but that is most likely. Hence I would also require a buck converter to step whatever down. I suspect the CT solution will be larger, but by how much remains to be seen.

Has anyone here done a proper investigation of the current transformer in an RCD? Everything I've seen so far on the 'net says things like "and this is the sense coil that is connected to this over my head circuit". Nothing about what waveforms/voltages/currents appear and when.

Cheers, MM.

mikeselectricstuff:
Modern rcds use electronics, with a capacitive dropper low voltage supply, and don't power the trip device direct from the ct output

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