Kapanadze Cousin - DALLY FREE ENERGY

[Jeg]

Easily.  Connect a smoothing/storage cap to the output--do not exceed the size listed in the spec sheet and you will be good to go.  Remember, the gate driver isn't delivering full amperage to the MOSFET gate for the whole cycle of the pulse.  It's a typical capacitor ramp-up curve; once it overcomes the initial charge disparity, voltage takes over and amperage drops off to nothing.

You are very right! I was always wondering how a simple lm7812 can provide 9A at gate side through a mosfet driver, the moment that 7812 itself can not give more than 1A.

Now if you really want to overcome the ringing associated with a MOSFET connected to an inductor, you can use a bipolar arrangement of these DC2DC convertors to force the MOSFET off.  How?    Just put two in series, this is your drive swing.  Say you use two 12 volt modules, in series this is 24 volts delivered to the gate driver.  Now level set the MOSFET by attaching the Source in between to two DC2DC convertors.  Now you will have -12 volts on the Gate when the MOSFET is off and +12 volts on the Gate when the MOSFET is on.  Why would you want to do this...?

Is that possible to make a drawing for this connection? I try to visualize it but i can't.

When you drive an inductor, what happens when you turn off the switch?  Recall an inductor fights a change in current.  It fights by way of creating a massive voltage potential.  And where does this potential go?   You have one side of the inductor fixed to the positive rail and the other side is essentially floating since you turned the MOSFET off.  So lets say the inductor and MOSFET Drain now shows a potential voltage of negative 40 volts.  Say what?  Yeah, that's inductive kick, CEMF, Lenz Law, whatever name you want to apply to it.  Look at where the Source of the MOSFET is connected--ground.  That should be zero volts rights?  And the positive rail should be say 24 volts right?  From the perspective of the inductor though, ground is now been pushed to minus 16 volts.  For a brief moment, what do suppose the voltage is at the Gate?  That's right, positive 16 volts referenced to the inductor.  Sixteen volts for a nanosecond is just enough for the MOSFET to begin to trigger again, even though the MOSFET driver tells it to be off.  The issue here is charge and its propagation speed.  It can get to the ground rail faster than it can get through the gate driver and back to the MOSFET Gate, so the MOSFET begins to switch back on.  You'll see this ringing on the scope when the MOSFET turns off with normal/simple drive circuits.

Also a very detailed explanation. I hadn't think that the capacitance between drain and gate can affect gate (which is normal), and so a negative value at drain side can present a positive spike to the gate!! I was looking at my gate oscillation trying to minimize it with a use of a parallel diode, but i hadn't ever wondered about why it oscillates.

So pulling the Gate negative reference to Source is one way to help with ringing; the other way is to ensure you don't turn off the current to the inductor so fast that it kicks back.  Do both and you will have a nicely optimized drive circuit.  Attached is another "snubber" circuit that helps with kickback.  You will notice those resistors are 10 watts dissipation and they do heat up.  You can probe around with the scope all day trying to figure out why.   

D1, thanks man! I will start to use this kind of snubber in my circuits. Indeed the heat across resistance is very high as recently i tried it. But i thought it was a design error, and i omit it. 

[Jeg]

The parts mentioned can be found in digikey or mouser.Circuit breaker are more like medium to slow blow fuse.Only difference it is resettable.

The last year and during ruslan experiments i have burn about 70-100 fuses on my mosfet board. I'll search for this resetable fuse. It might be a helpful addition for the job of exploring Ruslan's head!

[itsu]

Dog-One,  Jeg,

that is basically the same snubber setup as in Olegs green box setup, he has only 1 resistor while you have 2, see blow up below (ignore the red circle).
I tried it but it did not work for me, i still had massive ringing (1.4MHz) when the MOSFETs shuts off.

It would be good to see if Jeg has better results.


Presently i am changing the snubber setup to use a RC configuration as calculated by this website (using my 1.4MHz ringing):
https://www.maximintegrated.com/en/app-notes/index.mvp/id/3835


Regards Itsu

[itsu]

I reworked my Yoke driver board (push pull) to give an as clean signal as possible to the yoke for any future PLL usage.

I used this website to calculate the snubber values of the RC components:
https://www.maximintegrated.com/en/app-notes/index.mvp/id/3835
I must say that it worked very well.

The present used components can be seen in the below diagram.
(i have disconnected the VD6/7 diodes (see my earlier post) from Oleg green box snubber setup so these components are not in below diagram)

The 1st screenshot shows the MOSFETs gate and drain signals when NOT in resonance.
Yellow drain MOSFET 1 
Blue gate MOSFET 1
Purple drain MOSFET 2
Green gate MOSFET 2

I am puzzeled about the drain starting signal which starts high, then falls of to the normal 48V. What is causing that?
Also puzzeled about the gate signals which seems to "lag" its drain signal, how can that be?

The second screenshot is across the 40W/220V bulb which is attached to the grenade.


Video here:  https://www.youtube.com/watch?v=5-vilYPhNn4&feature=youtu.be

Regards Itsu

[magpwr]

I reworked my Yoke driver board (push pull) to give an as clean signal as possible to the yoke for any future PLL usage.

I used this website to calculate the snubber values of the RC components:
https://www.maximintegrated.com/en/app-notes/index.mvp/id/3835
I must say that it worked very well.

The present used components can be seen in the below diagram.
(i have disconnected the VD6/7 diodes (see my earlier post) from Oleg green box snubber setup so these components are not in below diagram)

The 1st screenshot shows the MOSFETs gate and drain signals when NOT in resonance.
Yellow drain MOSFET 1 
Blue gate MOSFET 1
Purple drain MOSFET 2
Green gate MOSFET 2

I am puzzeled about the drain starting signal which starts high, then falls of to the normal 48V. What is causing that?
Also puzzeled about the gate signals which seems to "lag" its drain signal, how can that be?

The second screenshot is across the 40W/220V bulb which is attached to the grenade.


Video here:  https://www.youtube.com/watch?v=5-vilYPhNn4&feature=youtu.be

Regards Itsu

hi itsu,

The bi-directional TVS diode 54Volts is not applicable for mosfet rated 200volts.The protection resistor for the gate can be increased to 10kohms.Although no issue using 2.2k at 18volts (8mA ea)

Sorry i have just seen the video.At 5+Amps at 24volts 120watt for lighting 40watt bulb.40/120 =33% efficiency.

That's the thing about using lower voltage mosfet.Alot of thing to factor in.

I do recommend using IGBT 1.2kv 25Amps rated  FGA25N120ANTD.

My 220volts 2000watt induction heater was using mere FGA11N120ANTD.11Amps rated.Reason being at higher voltage(mains) lower current is needed.


Please remove TVS Diode 54volts and implement a 200volts varistor.It's killing your efficiency.

My prototype snubber circuit(Not found in internet) which was not implemented for my PWM generator shown in video merely consist of 2.2nf 2kv caps and varistor value choosen base on around 1/2 the Vpp of the Bemf spike in series.It's implemented in my variable dc voltage generator up to 1600volts using 12volts as supply.