Anti-static electricity circuit

Thread Starter

q12x

Joined Sep 25, 2015
609
This is part of a bigger project I'm into. You can read all about it here if you like, but I suggest to concentrate on this particular problem I am describing here, since its a big subject and project already. In summary, in the summer and the autumn, this circuit had no problem when I changed its antenna length. But now, in the winter (and I understand its a seasonal thing) my 2N7002 transistor there gets burned if I touch it's antenna with my hand. I got a smaller length antenna until now, and the transistor got damaged, little by little, and I was troubleshooting something else, but now, me and a good friend here on the forums, mister @sghioto figure it out it was the electrostatic. I've already burned 4 transistors !
1613258433537.png
Ok, so I'm thinking to new approach, new tactics.
1- There are no anti-static electricity circuits? Already made? That I can copy and apply to my problem here?
Protection for static electricity, of any kind and any shape, not just electronic circuits, but materials perhaps?
2- Can't we invent such an anti-static electricity circuit? I imagine it should be with a rezistor and a zenner diode. I remember a zener diode needs a resistor, like a led, to limit current through it, or else will get burned. I think it was an article here on AAC. I dont usually use in practice very often the zeners, but I have a general idea about them and also I have a collection of them in my arsenal, all brand new and with many voltage values. I bought a set on ebay long time ago, just in case.
- If not with a zener, then with a voltage limiter, but it must be in form of "if voltage equal or greater than 15V, then limit it to this maximum of 15V".
3- Before breaking any more sensitive 2N7000 transistors, I would very much like to make a test circuit for this electrostatic problem. Something simple I imagine, with a couple of normal npn bc546 transistors and a led or multiple leds, to signal me when and how hard the electrostatic is occurring.
I dont have any circuit designed yet, I only have the ideas. Here I am asking for the circuit designs from you.
Or, if is too scify what I am imagining, then please explain it to me since its a new subject to me. I mean, its not new but I seriously treated now, than before.
Thank you !

PS> I got these ideas after you (@sghioto) mentioned " The maximum gate voltage on 2N7000 series is only 20 volts. " So in this context, it might be a chance.
 
Last edited:

Delta Prime

Joined Nov 15, 2019
998
Hello there :)
3- Before breaking any more sensitive 2N7000 transistors, I would very much like to make a test circuit for this electrostatic problem
Just to give you an idea of what you're in for you'll have to be able to absorb, deflect , insulate or attenuate.

Walking on a wall-to-wall carpet: 10 – 20 kV
Walking on a plastic floor (PVC): 2 – 5 kV
Walking on an anti-static floor: 0 – 2 kV
Lifting paper from a table: 5 – 35 kV
Rising from a chair: 10 -25 kV
 

Thread Starter

q12x

Joined Sep 25, 2015
609
Fantastic answer, thank you !
I also discovered what that SOI acronim means (Silicon On Isolation) that is often refer into the paper from the same website. http://www.ics.ee.nctu.edu.tw/~mdker/International Conference Papers/4.4-MDKer_Reprint.pdf
I got a similar answer in the original projekt page, and I asked my friend there what is the purpose of D2 but he abstain to answer. Now I understand why. I have many things to learn from you guys here.
Now Im worried if normal/common diode like 1N4001-7 or 1N4148 is enough, and if they are really using some special diodes just for this electrostatic discharge (ESD) problem. There are 3 types of diodes compared in this paper: a Lubistor diode, gated diode and non-gated diode. Lubistor diode is the normal diode used for ESD, while the other 2 are the new generation used or proposed to be used.
Screenshot_2.jpg
 
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MisterBill2

Joined Jan 23, 2018
8,752
Clampdiodes as shown will provide protection, but I advise adding a series resistor to limit current from any static that hits the antenna. a 1K resistor should be adequate.
 

Thread Starter

q12x

Joined Sep 25, 2015
609
Clampdiodes as shown will provide protection, but I advise adding a series resistor to limit current from any static that hits the antenna. a 1K resistor should be adequate.
Thank you ! In the original intervention from mister @sghioto he also added a 100ohm resistor as well and I included it in my real circuit. Actually is in series with a 1Gogm (reversed biased) diode. I will update soon the circuit I made and see how I put everything in it.
For now, it works. I wished the range to be greater than it is now... but im happy it works as it is.
I made a movie, a long one (12min), in which I present that it works. Nothing important in it. You can skip it.
 

MisterBill2

Joined Jan 23, 2018
8,752
The clamp diodes and resistor are a good start, but depending on the required frequency response a shunt capacitor also, between the diodes junction and common, would absorb the very fast rise portion before the diodes can switch on. The problem is that those static sparks do have an almost instant rise time, while most diodes have a measurable rise time. And there are even special capacitors with a loop thru made for exactly this purpose. But the ones that I have used are 0.001 MFD disc caps, usually rated for 100 volts, although 50 would be adequate.
 

Thread Starter

q12x

Joined Sep 25, 2015
609
The clamp diodes and resistor are a good start, but depending on the required frequency response a shunt capacitor also, between the diodes junction and common, would absorb the very fast rise portion before the diodes can switch on. The problem is that those static sparks do have an almost instant rise time, while most diodes have a measurable rise time. And there are even special capacitors with a loop thru made for exactly this purpose. But the ones that I have used are 0.001 MFD disc caps, usually rated for 100 volts, although 50 would be adequate.
Excellent idea with adding 2 additional 1nF capacitors. I really like it and I admire your thought of adding them. I could not think on adding them myself.
But for now is working and I will leave it a period as it is, in a test mode.
If I will remake this circuit module again, and is kind of in plan, because as discussed with mister @sghioto, he insisted on making the exact circuit as the original was. THough I encounter so many problems in the way of building this thing, I had to modify and dance around it until I see it work, so I got away a little bit from the original. But he pointed out to stick it to the original and thats why I say, it is most probably in plan to remake it. And if I remake it, I will definitely add the new caps as you are brilliantly suggesting here.
From what I understand, this is how to place them, correct?
1613463915729.png
 

MisterBill2

Joined Jan 23, 2018
8,752
Now you have the same input circuit as I used in an automotive tester box that I put into production back in 1979. There were a lot of those testers built, and they were very useful and never had any problems.
 

Thread Starter

q12x

Joined Sep 25, 2015
609
Now you have the same input circuit as I used in an automotive tester box that I put into production back in 1979. There were a lot of those testers built, and they were very useful and never had any problems.
What they were testing? Show me the circuit if you would like.
 

MisterBill2

Joined Jan 23, 2018
8,752
It was like the circuit you have, missing only that series diode. The resistor was 1K ohm, the capacitor was 0.001Mfd, and the diodes were 1N4148. They were protecting the inputs of a 74C04 , I believe.
 
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