Self running coil?

[gyulasun]

Hi Gyula,

thanks for the schematic. That's exactly how I had the 4N35 connected last night and I also had the 10K between the gate and source to shut the mosfet off.

I don't understand why it was only working at low frequencies I'll see if they really have the CNY17-3 in stock when I pickup the CMOS 555

Thanks for your help.

Luc

UPDATE

I just checked and they have the CNY17-3 in stock

Well, then probably the 10kOhm slows down switching, unfortunately. But if you reduce it to 1-2 kOhm or lower to increase speed, then power consumption from the capacitor goes sky high.

Yes I would agree with using the TC4804-05 opto MOSFET driver in itself, no need for the IRF640 then.  IF the TC4804 or 05 does not include the body diode for its output FET, you can connect a fast diode there instead.

rgds,  Gyula

[gyulasun]

Luc, I agree with Mike, I did not consider the flat on and off parts of the pulses, sorry.  This means that you would not have higher frequency success with the CNY17-3 either, maybe to as high as 10-15kHz.
Also the speed depends on the opto diode input forward current too. The higher the current is the speedyer the device is, up to the data sheet limits of course. And here we cannot spend current for speed.

Thanks, Gyula

[gyulasun]

Gyula,

Would it not be possible to simply attach only the signal generator to the mosfet and then connect the Cap to the source and drain, and just observe what goes into the cap ?

Actually a [known] voltage/amperage could be supplied to get it at the correct working point, but this can with a calculation be subtracted from the cap value later again?

EDIT: No need to attach battery I guess, since the signal generator can easily deliver enough voltage ?  Anyhow, after say 5 minutes of charge, one could see how much the cap collected.

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NextGen67

Hi,

After your message I have reconsidered what you suggested and I think a test would be worth doing as per your schematic in your above post.
I cannot forecast what the voltage might be in the cap.

If I recall correctly, Luc measured the drain source peak to peak AC voltage as about 3V in one of his videos. And then his input AC voltage was about 9V peak to peak across the gate source.  This would mean that just due to the gate source interelectrode capacitor (some hundred pF, voltage dependent) the 9V couples through 3V to the drain source side from the 9V but this is a guess from here because the schematic was the full circuit, not what you drew above.

Now that the high speed TC4804 or 05 MOSFET driver would make the IRF 640 obsolote in this circuit, maybe the question you pose is not a question any more? 

Thanks,  Gyula

[NextGen67]

Luc, I agree with Mike, I did not consider the flat on and off parts of the pulses, sorry.  This means that you would not have higher frequency success with the CNY17-3 either, maybe to as high as 10-15kHz.
Also the speed depends on the opto diode input forward current too. The higher the current is the speeder the device is, up to the data sheet limits of course. And here we cannot spend current for speed.

Thanks, Gyula

So, that means we are left over using the TC4804-05 opto MOSFET driver in itself (or similar types, this was the first one coming in mind).

It has a wide enough range for Frequency (up to 1.2Mhz), but you might want to take a look at the specs in the data sheet if there is no other obstacle... It's maximum voltage is also 20 volt.

The data sheet is attached in my message about the TC4804 earlier.

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NextGen67

[NextGen67]

Hi,

After your message I have reconsidered what you suggested and I think a test would be worth doing as per your schematic in your above post.
I cannot forecast what the voltage might be in the cap.

If I recall correctly, Luc measured the drain source peak to peak AC voltage as about 3V in one of his videos. And then his input AC voltage was about 9V peak to peak across the gate source.  This would mean that just due to the gate source interelectrode capacitor (some hundred pF, voltage dependent) the 9V couples through 3V to the drain source side from the 9V but this is a guess from here because the schematic was the full circuit, not what you drew above.

Now that the high speed TC4804 or 05 MOSFET driver would make the IRF 640 obsolote in this circuit, maybe the question you pose is not a question any more? 

Thanks,  Gyula

For me personally, I definitely would still like to do the test.  But it is up to Luc of course. It is a step that *could* be skipped using the Opto mosfet.  It is just that it would help me in estimating how great are the chances on success

EDIT: About the cannot forecast what the voltage might be in the cap, is exactly what I am searching for also, and this test would [likely] give some conclusions about that. Given a 5 minute time frame of loading or so, would give a really good indication of what is going on at the Gate side, and would help me to determine if my theory is correct.

[optionally, a voltage could also be supplied -together with the generator, to *simulate* a CAP charge-, as I mentioned in the previous message with the drawing, but then this *must* be a sharply defined voltage/amperage, so it can -calculative wise- later on be subtracted from the charge in the cap].

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NextGen67