Negative discharge effect

[ayeaye]

Ahh, a Zener diode, but then the backward current through it is also somewhat restricted. Drain-source breakdown voltage? It's 200 V by the datasheet. When its open then i think it should be on its internal drain-source on resistance, 0.4 ohms. But i still didn't understand, is that internal diode active also when the mosfet is closed, because during the back-emf the mosfet is closed.

Yes i ripped all my components from my old CRT monitor. The core is the deflection yoke core, and the wire i also got from the degaussing coil of the monitor.

[TinselKoala]

Ahh, a Zener diode, but then the backward current through it is also somewhat restricted. Drain-source breakdown voltage? It's 200 V by the datasheet. When its open then i think it should be on its internal drain-source on resistance, 0.4 ohms. But i still didn't understand, is that internal diode active also when the mosfet is closed, because during the back-emf the mosfet is closed.

Yes i ripped all my components from my old CRT monitor. The core is the deflection yoke core, and the wire i also got from the degaussing coil of the monitor.

At the end of the video I show the body diode of the mosfet being checked. Select "diode check" function on the DMM and place the Positive probe on the Drain pin of the mosfet. Make sure the mosfet is off by touching the Negative probe from the DMM to the Gate pin. Then put the Negative DMM lead on the Drain pin and the Positive lead on the Source pin. The DMM should read the fwd voltage drop of the body diode, something around 0.45 or 0.5 volt.

[ayeaye]

Ok, i understood now that the internal Zener diode is also active when the mosfet is closed. But we are talking about reverse current. So as i understand, this Zener diode opens when the reverse voltage in the circuit is more than the drain-source breakdown voltage of the mosfet, 200 V in the case of IRF630.

I don't know whether the back-emf is more than 200 V. But it's not only that. As i understand, a Zener diode acts reversely almost the same way as a normal diode acts when there is a forward current. That is, it always has the voltage drop equal to the breakdown voltage, which i understand is 200 V. But this does not explain why the voltage on both the source capacitor and the charged capacitor was almost equal, that is, the absolute value of the voltage was slightly greater on the source capacitor. If this were the reason of the negative charge, then likely the source capacitor had to have much less voltage on it, than the charged capacitor.

[TinselKoala]

Can you confirm the inductance value of the coil?

[ayeaye]

Can you confirm the inductance value of the coil?

The problem is, i have no good tools to measure. I measured it by connecting the coil and a potentiometer in series to a 12 V AC wall adapter, it was really 14.4 V. Then i adjusted the potentiometer so that the voltage on that was half of it, 7.2 V AC. Disconnected the potentiometer, measured its resistance and calculated the inductance by the 2. method there http://www.wikihow.com/Measure-Inductance , when changing the resistance instead of frequency. And with that method i got the inductance 6.6 H.

But then i tried to check that method and measure a known inductance. I had only a small known inductor though, and i don't have so small potentiometer, so i had to use small resistors. I also had to use a 100 ohms resistor to restrict the current of the adapter, to not to burn the adapter. This 100 ohms resistor went so terribly hot that i thought i can use it as a soldering iron. I measured the voltage of the inductor and a combination of resistors in series, and choose resistors so that their voltage was half of that voltage. I got that way 80 mH, but what was written on the inductor was 8,2 mH , that is, 8, what looked like a short vertical line, and 2. I thought that means 8.2 mH but i'm not entirely sure that the thing in between there was a dot, so maybe it was 82 mH.

The core is the core of the deflection yoke of a CRT monitor, and there is 900 turns of a 26 gauge magnet wire on it. I calculated the inductance, and got only 0.16 H. Assuming that the relative permeability is 100, but for such ferrite core it is likely much higher.

So this is what i could get with my primitive tools. As much as i remember,  the potentiometer was 2.2 k when the total voltage was 14.4 V, and there was 7.2 V on the potentiometer. Frequency should be 50 Hz. I measured in the 200 V AC range of my multimeter. So this is how it is, with primitive tools it is not possible to get too good results.