Mosfet stack for higher breakdown voltage

[Jeg]

Wow gyulasun..i was trying many days to find this article. Tnks for the link.

Tinsel i finally did it. From what i learn until now...

1. I doubt that schematic in fig.2 in the link i posted above works as it is. It needs lowering the 10M resistances. The reason is the leakage current between Drain and source. With resistances so large like the 10M, the voltage that mosfet's share is not equal. With pots in the place of these resistances, i found out that my IRFP460 stack, equalize the voltage at about 80Kohm

2. 12V for pulsing is not a good idea. 18V is better because Ciss and Crss are much much smaller!

3. The 3904 and 3906 idea is fine up to about 2KHz in my 460 stack. After 2Khz the switch starts to close. The reason is that it needs power. MC1406/7 puts out enough Amber to charge quickly the input capacitance. The above transistors in the mA range are not enough. In addition, this transistor driver doesn't work with voltages lower than 120V as in my 48V case. In case of using this driver, you have to change the 470pF if you have different than 1500V supply.

Does anybody have a suggestion for a dc to dc boost converter? I'd like to make 12V to 500V or higher, for making a bigger supply for the stack.

Tnks
Jeg
     

[TinselKoala]

@Gyula: Thanks! That's a very interesting paper. I especially like the transmission line gate driver arrangement. My old TinselKoil 2 uses a similar toroidal gate transformer arrangement to produce the out-of-phase drive signals for the two halves of the final mosfet H-bridge which drives the primary. Supplying enough current to these transformers was a bit of a problem; I used another H-bridge of bipolar transistors as a current amplifier and they do run hot. I suppose I should have used mosfet driver chips...

@Jeg: Yep, I agree completely. Thanks for the note on the schematic; when I build I'll probably have to do a bit of optimizing and value substitution.  Good luck on your project, I really am curious as to what your final product will be.

[Jeg]

Tinsel do you have a proposal for making high voltage supply with mosfets? I don't like transformers for some reason!

In the attached picture you can see  a stack of 14 Mosfets capable for handling up to 7000V. At least in theory... cause until now i have burned twice the hole stack. (28MOsfets!!!) My electr. components supplier is making good business with me!

[fritz]

very cool. congrats.
Using a cascade with HV diodes in combination with a H-bridge would give you some flexibility on voltage (#cascades + h bridge supply voltage) as well as current limiting (switching frequency).
rgds.

[gyulasun]

...
Does anybody have a suggestion for a dc to dc boost converter? I'd like to make 12V to 500V or higher, for making a bigger supply for the stack.

Hello Jeg,

You may find this link useful:  http://electronics.stackexchange.com/questions/31833/3v-to-500v-dc-converter

It refers to an EDN design idea article on a 1kV DC upconverter from 12V: http://www.edn.com/design/power-management/4334168/1-kV-power-supply-produces-a-continuous-arc

This page may also serve some food for thought: http://www.eleccircuit.com/dc-power-supply-300v-from-battery-12v/

Gyula