Kapanadze Cousin - DALLY FREE ENERGY

[TinselKoala]

Yep, the Schottky is a good idea.

Many folks who stress their mosfets will include a Zener gate voltage regulator diode, placed as physically close to the mosfet as possible, reverse biased, from gate to source. Since a solid 10 V is plenty to turn a mosfet on hard, I generally use a 12 or 15 V Zener here.  This will prevent the circuit's spikes from exceeding the gate-drain V limit and damaging the mosfet, usually.

The 840 is a workhorse, I use them a lot, but lately I have been liking the IRFP260N. It has much lower Rdss and if you are handling your spikes properly, seems rugged enough.

[verpies]

Many folks who stress their mosfets will include a Zener gate voltage regulator diode, placed as physically close to the mosfet as possible, reverse biased, from gate to source.

Zeners have small capacitance that increase the rise and fall times on the gate, because that capacitance must be charged and discharged by the MOSFET driver.  The capacitance is small but it's there.

Itsu's MOSFET driver can pull 8A down to ground so the Miller effect has no chance to add a significant voltage to the gate on the falling edge (especially if he tunes that "sink resistor").

On the rising edge, the Miller effect tries to pull the gate to ground as the MOSFET closes and pulls the drain to ground.
Itsu has some small ringing on the rising edge of the gate, but I think that's because his gate driver is too far away from the MOSFET (wire inductance).

I was going to suggest connecting a second identical MOSFET (Q2) with an non-driven gate shorted by a 1kΩ resistor (R4) to source, with drain connected to drain and source to source of the existing MOSFET (Q1).  The goal of this experiment would be to observe the voltage across the 1kΩ resistor (R4) and see how much influence the drain-gate capacitance can have on the gate of the second MOSFET (Q2).  This is only for curiosity and would have to be done when the first MOSFET (Q1) is loaded only by the 4.7Ω-10Ω load resistor (R3).

This experiment is not essential and it might be done only for curiosity.

P.S.
If the output of this circuit exceeds 3V then R4 should be decreased.

[mihai.isteniuc]

Hello 2 all. I think I have obtain the nanos we all are chasing ...

For references the scope settings are 0.5 microseconds/div with 2v/div and scope on 10x. supply tension is 150V with 100mA drawn from the source. Readings are done without any load exactly where the coaxial cable should be connected.

See the attached picture. Any opinions?

Mihai

[TinselKoala]

@Mihai:
So you are showing 0.5 microseconds per horiz div, which is 500 nanoseconds? You've got a falling edge that goes from its HV peak somewhere off screen, down thru the ringing back to baseline in around 250 or 300 nanoseconds. And the period of the ring appears to be around 100 ns or so.
Right?

Or does the "scope on 10x" statement apply to the horizontal sweep? , in which case you'd divide the numbers above by 10.  It's not clear to me just what you mean. Usually we use a 10x attenuating probe for voltage, so that's what I thought you meant. But if you  mean you've magnified the horizontal sweep by 10x, giving 50 ns per division, that brings your signal a lot closer to the "nano" range.

[Black_Bird]

Hello 2 all. I think I have obtain the nanos we all are chasing ...

For references the scope settings are 0.5 microseconds/div with 2v/div and scope on 10x. supply tension is 150V with 100mA drawn from the source. Readings are done without any load exactly where the coaxial cable should be connected.

See the attached picture. Any opinions?

Mihai

Are you triggering on the falling edge of the pulse or the rising edge? From my experiments, the fast rising pulse appears only with the load connected.