Self running coil?

[gotoluc]

He didn't state what the pictured circuit was, I see something resonating
nicely along at eight volts to the gate and and something else not resonating
very well as the load. The load Q~=1.0 and the phase shift is nearly 180
degrees out-of-phase with the input - that's hard to do. It reminds me of
that air core coil.

:S:Mark

Hi Mark,

the nice sine wave is the (Ferrite core) Pulse coil in Resonance. So the top peaks of the Sine Wave is what is switching the mosfet on and off.

I can now do this at any frequency from 5KHz to 50Khz

Luc

[gotoluc]

@Luc:

I just watched your video #13. Did i understand it correctly that the circuit runs without the function generator connected (only for starting it) and without any other outside connections ?

Yes skywatcher, you understood correctly. I can even start it just by tapping the positive connection. No signal generator even needed.

Luc

[gravityblock]

The other interesting finding I have is, the mosfet can self oscillate (switch) itself IF the right combination of inductance between the main coil and pulse coil (added between gate & source) as long as the circuit is tuned to the resonance range. By using a 3vdc feed, my dual coil toroid, IRF640 and tuning coil have achieved resonance to any frequency I want between 5KHz to 50KHz WITHOUT the use of capacitors. Many of the frequency Inductance values have been documented and someone from here is working out a formula that will be shared with all.

The above is the description to the best of my ability at this time of what is going on in the circuit at this time.

Hope this helps some to better understanding what I've been trying to share.

Luc

It appears the IRF640 is changing in capacitance according to the frequency.  The input capacitance of the IRF640 is 6 times greater than the output capacitance according to the specific test conditions from the manufacture (which the frequency may have a relationship to this input/output capacitance ratio, so the two coils would have this relationship in their inductance).  But then, you have the reverse transfer capacitance also, which could play a role in the formula.  This is my best guess since you're not sharing the frequency inductance values with the rest of us.  I guess everybody else here is incompetent, except for the one person you shared the values with.

Could you please post the data, so others can work on a formula also.  I probably won't be able to figure it out, but I like a good puzzle.  We may have a better understanding if you share with the rest of us, instead of sharing with a single individual.  We don't have a diagram of the circuit or any data with this new setup.  This is B.S.  You call this sharing?  I thought we were a community, working together to find a solution.

Thanks

GB

[NextGen67]

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Hi Luc,

Thanks for the answers, please when you have time measure the toroidal coil's inductance you have had in the oscillator with the scope shots. Is it still 113.5mH? Also, would be good to know the pulse coil's inductance and DC resistance, when separated from the gate-source pins, ok?

I do not agree that the IRF640 does not use external energy for its operation, sorry. The 3.8 mW or so power must be the reactive power inside the pulse coil which must be parallel resonant with the gate-source and gate-drain capacitors. This resonant circuit receives energy kicks from the drain pulses via the gate-drain cap, (C_rss) the latter acting as a coupling capacitor.  The drain side voltage pulse has a low duty cycle and the toroidal coil is not in resonance. 

This circuit you tuned with excellent ingenuity to perform as the scope shot shows and consume just 14uA from 3V reminds me to a Class C oscillator circuit, here is such with a bipolar transistor:

http://www.tpub.com/content/neets/14181/css/14181_80.htm

Yours would be called tuned-gate Hartley oscillator. In the above link, the L2C1 circuit receives energy kicks from the collector side via the coupling coil, L1.

This is the key explanation there: "Once every cycle, the transistor conducts for a short period of time (class C operation) and returns enough energy to the tank to ensure a constant amplitude output signal."

In your case, the MOSFET is able to conduct when the positive voltage peaks across the pulse coil are just over the MOSFET V_th threshold gate source limit, this means when the positive sinus wave goes above 2V (lower limit for the IRF640) with respect to the source i.e. when it comes up from the negative values via zero crossing and climbs up to its peak value, just reaching and passing through the threshold limit, the FET switches ON. 

I agree with you that the MOSFET capacitances contribute to the operation of this oscillator, and at the gate source side the C_iss resonates the pulse coil at 20 kHz.

<...>

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Comments are welcome from other members too.

Regards,  Gyula

Hi Gyula,

The inductance of the main coil depends on the frequency specified for the resonance to happen... So at for example 8Khz, the main coil mH is much higher then when the circuit is operating at say 20Khz.  We might say it the other way around.. The inductance mainly dictates at which frequency the circuit would work [this is in combination with the given mosfet due to the mosfets Capacitance].

The pulse coils inductance is again depending on the inductance of the main coil... I *think* the resistance of the pulse coil was rather high... some 50 Ohm or so... not sure. Maybe Luc can tell.

I do not agree that the IRF640 does not use external energy for its operation, sorry. The 3.8 mW or so power must be the reactive power inside the pulse coil which must be parallel resonant with the gate-source and gate-drain capacitors.

Not sure how to interpret this? I think Luc refers to the fact that the switching energy needed for the mosfet itself, *might* be greater then what the circuit as whole is consuming.... Say at 8Khz, 3Vdc the circuit takes 0.000014A, which would be 42uW of consumption. Then *if* the mosfet would use some 3+mW or so for its *own* switching, then where is that coming from, because the circuit only uses 42uW in the first place. In other words, does the [in this case] IRF640 switched at 8Khz uses more or less then this 42uW of energy normally for it's switching. I agree however that this 42uW is coming from a battery or capacitor.

I think the key point in here is determine *exactly* what the IRF640 would theoretically consume in energy when it is being switched on and off at the 8Khz rate, with the given info, as we know the circuit energy usage as a whole.

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NextGen67

[NextGen67]

It appears the IRF640 is changing in capacitance according to the frequency.  The input capacitance of the IRF640 is 6 times greater than the output capacitance according to the specific test conditions from the manufacture (which the frequency may have a relationship to this input/output capacitance ratio, so the two coils would have this relationship in their inductance).  But then, you have the reverse transfer capacitance also, which could play a role in the formula.  This is my best guess since you're not sharing the frequency inductance values with the rest of us.  I guess everybody else here is incompetent, except for the one person you shared the values with.

Could you please post the data, so others can work on a formula also.  I probably won't be able to figure it out, but I like a good puzzle.  We may have a better understanding if you share with the rest of us, instead of sharing with a single individual.  This is B.S.  I thought we were a community, working together to find a solution.

Thanks

GB

Actually the capacitance [for any mosfet] is changing according to the given voltage, so you could actually keep the capacitance the same for any given frequency... Only need to adjust the coils inductance of course.

Yes, the two coils will definitely have their relationship, that is why the pulse coil it's inductance is depended on the main coils inductance. It *might* be possible maybe to come up with a pulse coil that adjust itself according to the inductance of the main coil.

I'm sure Luc will post some data later on, but I can imagine he's rather busy with things, and he might want to include some other models then only an IRF640? Because that would allow anyone to figure out better how to work out the relationships, so that a formula can be determined that works in any given situation and with any mosfet one plugs in [of course would need to know the mosfets specifics for that, and the capacitance of the mosfet would need to allow for a certain 'off' range].

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NextGen67