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Registered Member #89
Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145
Also when I was saying Ohm, I was using the diode test, but now I understand that a zener isn't showing a reading of 1100~Ohms, it's it's forward voltage rating? 11v.
Actually 1100 mV would be correct - seems a bit high according to what I said before, but I don't even remember when I actually took notice on zener's forward voltage (so I might be wrong, it might be higher than of tipycal diodes). I'd give it a pass at 1100mV...
I also used this Nothing though.
Can you elaborate your "nothing" by the way? Don't use your meter for this, but a 9V battery, resistor and LED. Or a small incandescent bulb. If the mosfet doesn't have the particular "memory" on it's gate, which is a capacitor, it's fried - if it conducts D-S even if you shorted G-S, it's fried. If it conducts from gate to anywhere, it's fried. (note there's a diode in S-D direction, which will actually test as a diode with your meter when the device is off!)
I'm sure that with a few more attempts (try using a new mosfet first) you'll get a good feeling of it. I'm surprised you haven't already became fascinated with possibility of making a "touch switch" with a mosfet this way!
BTW, is there really any particular reason you insist on buying from digikey rather than a local shop? I wouldn't want to pay their postage just for a few mosfets and zener diodes, even if the local electronics shop wasn't closest to me :P
Registered Member #89
Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145
Platinum wrote ...
The source can conduct to drain, but not gate, this is also the same with the other 250n.
I don;t have a 9v bater so I used a 3.8v battery, and nothing happened.
Well, 3.8V is too low to turn the mosfet ON properly, if at all. That's why I advised against using a meter to test mosfets - they likely won't put out sufficient voltage to drive the gate on. 8-9V is about the minimum I'd use for these tests.
I guess you could pull a 9V battery from your meter though, or use your 12V supply/wall wart/ anything you have there.
If you don't think LED is clearly visible, you can use anything like a bulb, small motor, a beeper, etc...
Registered Member #3926
Joined: Fri Jun 03 2011, 08:32PM
Location: UK.
Posts: 525
I'm nearly crying atm, I put the MOSFET's back on, removed bad zener, turned my 19v 3.25a PSU on, and my arcs are back, I don't know wth happened but I'm very happy, I must thank you Marko, thanks very very much!!!
Does this mean I must add a 12v zener to the gate of the other MOSFET?, yet it's working on 19v.
Also arcs in the flyback haven't degraded, still same efficient.
Registered Member #89
Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145
I'm nearly crying atm, I put the MOSFET's back on, removed bad zener, turned my 19v 3.25a PSU on, and my arcs are back, I don't know wth happened but I'm very happy, I must thank you Marko, thanks very very much!!!
Well, then your mosfet testing methods aren't right probably. If you still can't locate the mosfet pins, I guess then it's time to learn that every mosfet has a datasheet! :P With a clear picture in it. I bet your led was kept lit just because you swapped the D-S again.
I think you should make that your next project, finally learning how mosfets work and how to test them properly! :p
The zener in this circuit serves to protect the mosfet gate. The circuit will work without it until the gate voltage gets too high for whatever reason and kills the mosfet. So buying a handful of zeners (rated 1W + ) probably wouldn't be a bad idea at all. I wouldn't run the circuit from 19V supply with the osfet gates being rated for 20V.
Registered Member #89
Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145
Platinum wrote ...
Yes, I will buy some zeners, thank you though!
No problem sir :P
BTW, just noticed the link you posted.. the circuit in the picture honestly looks somewhat shitty to me. IMHO if you really paid 30 pounds for it, you were ripped off :)
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I've now ACTUALLY got an ignition coil.
