Self running coil?

[gotoluc]

Hi Mark,

But Luc has been putting the 100 Ohm resistor in series into the gate circuit you must have missed that.   He showed actual scope shots already taken directly across the series 100 Ohm, see here the waveforms (click on the quote's link in bold just in next line):

Yes Mark! the 100 Ohm resistor has been there for some time.

It is unusual to place a series resistor into the Ground wire instead of the "hot" gate wire BUT it is equivalent as long as the circuit to be measured is GND independent and the signal generator GND does not meet with the GNDs of any other measuring instruments used. In Luc's setup this is nicely met.  This way Luc solved the problem that his two channel scope inputs have a common GND.

rgds, Gyula

Yes Gyula! exactly why I have it on the SG ground, so I can use both probes at the same time since they have a common ground.

Luc

[mscoffman]

@ everyone,

what do you think of the following mosfet specs.

www.irf.com/product-info/datasheets/data/irlml2502.pdf

www.irf.com/product-info/datasheets/data/irlml6402pbf.pdf

www.irf.com/product-info/datasheets/data/irf7700.pdf

I'm looking for a 20v mosfet that I can buy on ebay and the above are available

Luc

---

You should try a termination resistor on your signal generator
with the 2Sxxx transistor. to see if you can clean up its operation.
This transistor is the best you've tried in terms of lowering
gate energy but input noise is now beginning to get the best
of it. Any overunity detected?

---

Boy, these are a mixed bag;

www.irf.com/product-info/datasheets/data/irlml2502.pdf
- Yes, Moderate Ciss = 760pf (could do better but is OK)

www.irf.com/product-info/datasheets/data/irlml6402pbf.pdf

- P channel mosfet is a different device!...Would require wiring changes
to put mosfet towards positive battery above coil...gate pulls down
to turn On. Compatible with opto NPN bipolar output transistors. Check
Drain, and Source connections Specs are OK. Ciss=644uf Moderate,
I am not against it. Compatible with NE555 output...Don't
know about SG3525 compatability (probably not -circuit maybe
reconfigurable)

www.irf.com/product-info/datasheets/data/irf7700.pdf

- P channel mosfet a different device!...
Ciss = 4.3nf => no good, way too high, a high current DC device _
I am against it.

:S:MarkSCoffman

[gotoluc]

Hi Mark,

thanks for the reply.

My singal generator has a 50 Ohm impedance I think. Model Wavetek 134

Are you saying to add a 50 Ohm resistor between the hot and ground of the Wavetek and connect from the resistor to the gate?... if so, I did try it and still have the sine wave across the 100 Ohm current shunt.

Thanks for your input on the mosfets. I did not notice some of them were P channel. It should not be a problem but would use them only if the specs were great. Did not notice the other one was in nf

If you can have a look on eBay .com to find a better spec one then the irlml2502 would appreciate it.

Thanks for your help and time.

Luc

[gotoluc]

Hi Mark,

here are the scope shots. First is with 50 resistor and second is without resistor. I do agree that it makes the pulses square but it takes more current then without the resistor.

Both were adjusted to minimum voltage to trigger gate.

Any idea why this is ... this is the problem I have when I connect the 555. It keeps the pulses square and does not give as good of results compared to using the wavetek with rounded pulses.

Luc

[gotoluc]

@everyone,

decided to try Triangle wave to trigger the mosfet and it works!

With the scope shot below I have 0.26vdc on the pickup coil 1K resistor and -.000010 returning to cap bank with attached 12.88vdc battery.

Less current through the shunt. I also had to drop the volts division to 100mv to show more details.

Luc