Kapanadze Cousin - DALLY FREE ENERGY

[itsu]

I was missing the scopeshot across the CSR when the primary of T1 was connected in series with it.

Well i did not make a video when i blew up my MOSFET, but this afternoon i succeeded again doing so.

I made a video with my Iphone hoping it was of a better quality, but i needed to turn it 90 degrees, so its kind of crappy, sorry about that, i will stick to my Sony.

New MOSFET   driver (max4420), 0.1 Ohm resistor in series with 12 turns secondary, first video with 40V on the drain,  2e video with 200V on the drain.
No spike suppressor (1nF   1KOhm resistor) attached, no 10 Ohm resistor from gate to ground.

Finally when i barely touched the pulse width multiturn pot, i blew up again my MOSFET (humming of the 200V transformer).

Now the pulse in use was only 20ns or so, so not sure why it blew now, luckily the driver is still OK.

Video's here:


http://www.youtube.com/watch?v=J2f2tvS5-2Q&feature=youtu.be

http://www.youtube.com/watch?v=BZsRQylvorU&feature=youtu.be

Regards Itsu

[verpies]

but, applying signal to the gate only allows the voltage equal to the gate to be on the emitter... it's not a relay, huh?

BJTs are not voltage devices - they are current devices. They don't have gates, they have bases.

They can be connected in three ways:
1) For emitter follower configuration V_OUT = V_IN - 0.6V
2) For common emitter configuration the transistor behaves like an imperfect relay if the base is saturated with sufficient current.
3) N/A

Read this if you want to understand more.

[verpies]

Now the pulse in use was only 20ns or so, so not sure why it blew now, luckily the driver is still OK.

Because when the MOSFET opened then the current flowing in T1 primary had nowhere to go, and T1 rebelled by trying to generate such a high voltage that the current could flow in it anyway. 
T1 won by forcing the current to flow in your scope probe's capacitance (causing those LC oscillations) or exceeding the maximum voltage rating of the MOSFET source-drain junction, breaking through it and forcing it to conduct current anyway.  This junction breakdown permanently damaged the MOSFET.

The more current you will allow to build up in T1, the harder it will rebell when you try to interrupt it. That's why even a tiny pulse width increase will lead to a higher amplitude of the flyback pulse.

Previously, you were blowing MOSFETs because you were exceeding their maximum drain current (by allowing the inductor current to ramp-up too high during excessively wide pulse) and now you are blowing MOSFETs because you are exceeding their maximum allowable voltage rating (due to missing snubbers or flyback recovery circuits).
Look up Safe Operating Area (SOA)

The solution to this overvoltage during the flyback pulse is still a snubber (e.g. a Transil with breakdown voltage lower than the maximum V_D-S of the MOSFET or an RC dumper like the one you removed) or flyback recovery circuits like the one in T2. 

In the end: current in any inductor cannot be interrupted - it has to go somewhere and it will find its own way!!!
That's why it's better to give it your way...

P.S.
I am waiting for d3x0r to run into a similar BJT overvoltage junction breakdown problem, because he is carelessly opening his inductive circuits, too
Fortunately for his transistors, his power transfer in T2 is soooo low, that he does not have enough power to do any serious damage, yet.

[verpies]

@Itsu
I could not see any sign of T1's core saturation on your video at this horizontal scale.
Try to decrease the ns/div on your scope

Also, try to measure the inductance of T1's primary with an inductance meter (at the highest testing frequency, if you have that choice) and with your scope using the calculation L=V*dt/di ,e.g.: 150V*5ns/10A = 75nH, and compare these two measurements.

[itsu]

@ verpies,

Because when the MOSFET opened then the current flowing in T1 primary had nowhere to go, and T1 rebelled by trying to generate such a high voltage that the current could flow in it anyway. 

ok, that i can follow, but why is it then that i can vary the voltage on the drain between 0 and 200V without any problem on a fixed pulse width (still opening the MOSFET and current to flow every 10Khz or so), but when i change the pulse width a tiny fraction it blows the MOSFET.

Remind you there is no heat at all noticeable at the MOSFET and/or heatsink.
(this confirms kind of that it is the voltage that kills the MOSFET, not the current).

Regards Itsu