Self running coil?

[MasterPlaster]

This is a very informative video on magnetic transfer.

http://www.youtube.com/watch?v=mLd_py1xTO8

[xenomorphlabs]

@Gotoluc: When you construct a coil of bigger dimensions and higher inductance, so that you can push the 555 frequency below 2-3 kHz then you could use an optocoupler or photovoltaic driver like PVI1050N and possibly exclude the suspicion of power being transfered from the 555 circuit via the MOSFET and being solely responsible for the operation of the circuit without battery. A tiny audio-application 1:1 transformer might work for higher frequencies to isolate the MOSFET but most likely it`s inductance will need to be taken into consideration for the oscillation circuit.
Just a thought, keep it up!

[mscoffman]

@xenomorphlabs

The optoisolator is a good idea...I'm sure there are some that operate
at 1Mhz. Any AC or DC flowing to the gate will have been developed all
on the coil side, except for a very small capacitive coupling as listed on
its specification sheet.

Also, he can use capacitive coupling to the mosfet. Assuming a 16percent
pulse duty cycle the low will sit at/near ground. Just increase the capacitance
until the signal looks about the same on both sides of the cap. That will
block any unwanted DC from flowing to the gate. Also, decrease the drive
signal until it is 2.5+0.7 = 3.2*vpp* using a resistive voltage divider on the IC
side. He is overdriving the mosfet that should have voltage gain of 1.0e^6.,
and at 19Khz the signal is not RF. The above is called interstage coupling.
The opto is the best idea though it will block DC and most AC from the driver.

:S:MarkSCoffman

[gyulasun]

Hi Folks,

I see this problem differently.

I think the problem is not 'overdriving' the MOSFET gate with DC and AC which then leaks through. 
The problem is the MOSFET itself that has interelectrode voltage dependent capacitances, so it is very far from an ideal switch in this respect.
If you accept Luc used the MOSFET's output capacitance as the C member of a resonant LC tank circuit, then it will be the same whether you use opto coupling at its gate input.  And the MOSFET's gate-drain capacitance will also remain the same value as the data sheet says, where the input pulses can leak through regardless of the input opto.

The better solid state switch would be like a low power photovoltaic relay, this still has an output capacitance of some hundred pF at low operating voltages but at least it has a high input-output isolation. Like this (but other firms may have a better product already):
http://www.irf.com/product-info/datasheets/data/pvg612.pdf

@Mark, I do not get this:

"Also, decrease the drive signal until it is 2.5+0.7 = 3.2*vpp* using a resistive voltage divider on the IC side."

What is the 2.5V and what is the 0.7V?

Thanks,  Gyula

EDIT:  The opto isolator is a good solution in input-output separation, but the power MOSFET high (nanoFarad) output capacitance with its voltage dependence stays the same.

[gotoluc]

Hi everyone,

I have some good news.

As I write this the coil is self running (NO BATTERY ATTACHED TO CAP BANK) and the voltage is at 19.45 Volts DC and rising

I also added a pickup coil with diode, capacitor and 50K Ohm load and it is at 1.03 volt dc.

I changed my MOSFET gate driver to a SG3525A circuit which I built some time back and immediately had much more success compared to the 555 PWM.

Here is the new video: http://www.youtube.com/watch?v=_sicsnUq_a4

The core of the toroid is a regular ferrite 1"-3/8 OD, 13/16" ID and 7/16" high. The coil is wound 5 layers of 24 AWG on each half. One wound CCW and the other CW. Inductance is 1,050mH and 7.6 Ohms with coils bridged together.

I will be limited in time to answer questions for the rest of the week.

Luc

Here is a base circuit for the SG3525A: