Kapanadze Cousin - DALLY FREE ENERGY

[Hoppy]

The Transorb or Transil can have several nF of internal capacitance that needs to charged and discharged, even if the Transorb does not avalanche and this capacitance will degrade the gate signal. I read somewhere about Transorbs with pF internal capacitance, but I never used them.

I don't think Itsu has a problem with overvoltage at the gate.  His MOSFET driver cannot exceed the maximum voltage rating of his MOSFET's gate and any eventual Miller effect, caused by the drain-gate capacitance, is effectively attenuated by the 10Ω between the gate and ground.
That 22Ω resistor would form a voltage divider with Itsu's 10Ω gate-source resistor and that would degrade the gate voltage significantly during the on-time.
Itsu's gate driver is strong enough to ovecome the 10Ω resistor and charge the gate quickly during the on-time, but without this 10Ω resistor Itsu's driver is not strong enough to discharge the gate quickly and turn-off the MOSFET quickly.
Some of the newer MOSFET drivers address this problem by providing 2 times more gate discharge current than gate charge current (e.g. the UCC27511 )
Ferrite beads might help, if Itsu has problems with gate breakdown due to high voltage spikes on the gate, ...but does he?
Maybe. He already is pulling 25A for 40ns with his MOSFET - that;s pretty good.
Do you think he needs more current?
Regards
Hoppy

Fair point about the 22R resistor. I had not realised that Itsu had a 10R between gate and ground.

The transorb must be rated at a minimum of 24V and preferably 30V. I have used both the P6KE 30A and SA24A and from my findings, both exhibit negligible degradation of the gate signal.

At the moment we have little idea of how much current is needed to saturate a toroid of the size and build specified. Looking at average currents I listed for my setup, rather than extremely short duration peak pulse currents, I cannot see how current at this level is going to heat the core sufficiently to warrant a heat sink as specified by Dally. Based on this, then more current may be necessary but the inverter shown in the schematic is IMO inadequate to provide a lot more power. If core heating is an indication of core saturation at the required level for this application, what temperature range should we be looking for?

Regards
Hoppy

[itsu]

Hoppy,

Сергей Ð'. wrote in this thread on 3 Oct.:

To make several kV Nano-Pulser pulses use several diodes serially. Ferrite ring i think you can find easy. You may use bigger ring up to 2 cm outer diameter.  Ðœ6000НМ or better.
Ferrite is going hot so must be sealed or glued on KT926 radiator. And connecting wires must be as short as possible if you want nano pulses !! For Ferrite ring use quality teflon wire or wire which isolation can handle more than 200 degrees temperaure. This is important coz Ferrite ring, Transistor and DSRD will running continuously. Use good radiator for DSRD diode!!

So i guess the toroid can heat up till 200 degrees Celsius.



Black_Bird,

Are you using the 220uH at the VDD line with the 2 uF capacitor to ground?

no i am not as i thought this would only be needed in the final circuit and not while testing for saturation.   
But i could add it anyway, perhaps it helps.


Regards Itsu

[Black_Bird]

@itsu

I think it will help, at least may avoid burning your MOSFET again.

[Hoppy]

Hoppy,

Сергей Ð'. wrote in this thread on 3 Oct.:

So i guess the toroid can heat up till 200 degrees Celsius.


Regards Itsu

My teflon wire is rated up to 200 degrees C but that's mighty hot! I just cannot see how that could be achieved with Dally's inverter. The 220uH choke will also get mighty hot.

Regards
Hoppy

[Black_Bird]

@hoppy

I don't think the 220uH will get that hot, because it actually averages the current on the toroidal transformer. The duty cycle is very low, so that the average current will be low.