Self running coil?

[gotoluc]

Thank you Luc, and please one more data: a single layer of (any) number of turns gives ? uH or mH,  I know somewhere it could be found too...

Thanks, Gyula

Okay Gyula,

I wound 12 turns (first layer) of the 30AWG or 0.25mm wire on the toroid core which takes 35mm of wire length per turn and that gives 187uH / 12 = 15.58uH per turn on first layer

Luc

[gyulasun]

Thank you Luc, now using your OD=34.5mm ID=20.67mm and (average)height=10.6mm 

the software gave  for A_L=1298,61nH/N²

and for permeability it gave u=1195.7 

Thanks,  Gyula

[gotoluc]

At everyone,

I think I found something important that is preventing the circuit to show its full potential.

I decided to reproduce as close as I can the sine wave signal the self pulsing coil produces when connected between the gate and source of the mosfet. Using my Signal Generator in sine wave I matched the frequency and adjusted the output to the exact vpp the pulse coil produces. Once I had them matched up as best I can I pulled out the pulse coil and connected only the generator. To my surprise the current draws is exactly the same as when the Pulse coil is connected and self pulsing. I would of though it would use less current since the switching is now powered by the generator! However this is not the case and I also found something even more important.

See the first 2 scope shots below to see first the pulse coil (self pulse mode) shot and next the generator pulsing the circuit.
All tests are using the same 3vdc feed and IRF640 mosfet with same dual coil toroid @ 1075mH (no magnet)
Green scope probe is between mosfet drain and source and Yellow scope probe is between mosfet gate and source.

Why is this important!... because ever since I've been using the pulse coil I lost the ability to control the mosfet switch on timing. If you look at all the scope shots I posted before, when using the pulse coil you will see it has this delay. However if I use the generators I can adjust the on time timing.

So without changing the setup I only turned the micro frequency adjustment on the generator to make the mosfet turn on time sooner and bingo!... no current used and as I keep going it starts to send back current (up to a certain point). See those scope shots below the first two.

It is clear that the pulse coil is delayed too much. We will not get it to use no current or send back current this way. We need the mosfet on pulse trigger to be earlier for this to work.

What do you think?... any ideas how to solve this?

@Gyula, please notice that the main coil bump is still there (without the pulse coil) so this is not what we think it is!... notice it goes away when on time is advanced to starting to come back but in negative as it send most current back. What could this be?

Luc

[chadj]

At everyone,

I  I found something important that is preventing the circuit to show its full potential.

I decided to reproduce as close as I can the sine  signal the  pulsing  produces when connected between the gate and source of the mosfet. Using my Signal Generator in sine wave I matched the  and adjusted the output to the exact vpp the pulse coil produces. Once I had them matched up as best I can I pulled out the pulse coil and connected only the generator. To my surprise the current draws is exactly the same as when the Pulse coil is connected and self pulsing. I would of though it would use less current since the switching is now powered by the generator! However this is not the case and I also found something even more important.

See the first 2 scope  below to see first the pulse coil (self pulse mode) shot and next the generator pulsing the circuit.
All tests are using the same 3vdc feed and IRF640 mosfet with same dual coil toroid @ 1075mH (no magnet)
Green scope probe is between mosfet drain and source and Yellow scope probe is between mosfet gate and source.

Why is this important!... because ever since I've been using the pulse coil I lost the ability to control the mosfet switch on timing. If you look at all the scope shots I posted before, when using the pulse coil you will see it has this delay. However if I use the generators I can adjust the on time timing.

So without changing the setup I only turned the micro frequency adjustment on the generator to make the mosfet turn on time sooner and bingo!... no current used and as I keep going it starts to  back current (up to a certain point). See those scope shots below the first two.

It is clear that the pulse coil is delayed too much. We will not get it to use no current or send back current this way. We need the mosfet on pulse trigger to be earlier for this to work.

What do you think?... any ideas  solve this?

@Gyula, please notice that the  coil bump is still there (without the pulse coil) so this is not what we think it is!... notice it goes away when on time is advanced to starting to come back but in negative as it send most current back. What could this be?

Luc

Gotoluc,

First, I think you should be driving your MOSFET with only rectangular pulses. Any time the MOSFET is partially on the resistance increases and you burn power.

The drive current on a MOSFET is next to nothing because the gate is capacitive. It takes current to fill the capacitive gate but it should not pass through to the source. Make sure the drive voltage is as close to the positive rail as you can get or you may not fully switch the gate. A driver circuit is good at doing this because you can take a weak 3V pulse and drive a 50V MOSFET with it.

Am I correct to assume that your signal generator can't change the duty cycle? This is a problem as I predict you will get better performance with a high volt, narrow, and correctly timed pulse. Can you do this with your 555 circuit?

Also, if you want the coil to trigger the MOSFET at a different delay you can drive the 555 in monostable mode to adjust the timing however you want.

I use a Rigol DG1022 signal generator and it is awesome if you have $700 to burn. Absolutely the best buy out there...

http://www.tequipment.net/RigolDG1022.html

Chad.

[gotoluc]

Gotoluc,

First, I think you should be driving your MOSFET with only rectangular pulses. Any time the MOSFET is partially on the resistance increases and you burn power.

The drive current on a MOSFET is next to nothing because the gate is capacitive. It takes current to fill the capacitive gate but it should not pass through to the source. Make sure the drive voltage is as close to the positive rail as you can get or you may not fully switch the gate. A driver circuit is good at doing this because you can take a weak 3V pulse and drive a 50V MOSFET with it.

Am I correct to assume that your signal generator can't change the duty cycle? This is a problem as I predict you will get better performance with a high volt, narrow, and correctly timed pulse. Can you do this with your 555 circuit?

Also, if you want the coil to trigger the MOSFET at a different delay you can drive the 555 in monostable mode to adjust the timing however you want.

I use a Rigol DG1022 signal generator and it is awesome if you have $700 to burn. Absolutely the best buy out there...

http://www.tequipment.net/RigolDG1022.html

Chad.

Hi Chad,

thanks for posting these details

I do agree with you on what you posted if this was a normal electronic circuit. However this is not a normal circuit. I have tried the suggestions you have posted before.

The thing is the circuit naturally creates the sine wave once the main coil starts to resonate and doing the things you suggest above I've concluded will affect the natural way the circuit wants to function.

The 1st Scope shot below is so far the best score mosfet IRFBC20
With 3vdc at 10KHz with main toroid at 337mH and pulse coil at 225mH the circuit operates with just 4.3uA

The 2nd Scope shot below is the next best mosfet IRF640
With 3vdc at 10KHz with main toroid at 165.3mH pulse coil at 96mH the circuit operates with 9.4uA

So it does look like a mosfet of a lower capacitance like the IRFBC20 is better for what I'm trying to do.

Thanks for sharing.

Luc

ADDED

I added a red circle to each shot so you can see for yourself that it is in fact the advance timing of the pulse coil that gives the saving as I stated in my post above.