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substitute for HV mosfet ?

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paris

Thu Oct 22 2015, 01:47AM

Registered Member #3042 Joined: Wed Jul 28 2010, 12:36AM
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Posts: 121

Im looking around for IXTX20N150 power mosfet 1500 v 20A .

mouser have them , not cheap but I was wondering if a lower volt mosfet could be used with hyper fast diode on either the drain or source in order to bump its v rating up ????

does that sound like an idiot at work? or would it work?

cheers

dexter

Thu Oct 22 2015, 05:34AM

Registered Member #42796 Joined: Mon Jan 13 2014, 06:34PM
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Posts: 195

in what configuration do you plan to use those mosfets?

paris

Thu Oct 22 2015, 08:21AM

Registered Member #3042 Joined: Wed Jul 28 2010, 12:36AM
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just using 1 for an experiment FBT , I thought maybe if hyper fast diode was on Drain side , thatd compensate series voltage rate being fast acting....

the diode is RHRG30120 , 1200 or 1500 v rated

the mosfet NEEDED is IXTX20N120 , 1500v 20A , I thought maybe a lower volt mosfet + diode would make up for it .

Digikey has the mosfets but 30 @ $520 is steep for a play around

the circuit was drawn up by EE to try to substitute SITh thyristor by NGK which is unavailable to the public !

Ill prob have to shell out for 20N150 thru mouser just thought there might be a way around it

dexter

Thu Oct 22 2015, 11:39AM

Registered Member #42796 Joined: Mon Jan 13 2014, 06:34PM
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i don't think a series helps that much

the single case i used diodes with the mosfets is when i want to bypass the mosfet internal diode but this uses 2 diodes in this configuration

but with the current day mosfets i doubt it justify the extra cost

Wolfram

Fri Oct 23 2015, 01:53PM

Registered Member #33 Joined: Sat Feb 04 2006, 01:31PM
Location: Norway
Posts: 971

The suggested diode will not help. For the flyback circuit, you want a high forward breakdown voltage in the off-state. The diode will increase the reverse breakdown voltage which doesn't help. The suggested bypass diode will shorten the reverse recovery time but it will also not help with the forward breakdown voltage.

I would suggest an IGBT instead of the MOSFET. When you want a high breakdown voltage, IGBTs generally have significantly lower conduction losses. The MOSFET you suggested has an Rdson of 2.3 ohms at 125 degrees junction temperature (not unrealistic). If the RMS current is 10 amps, conduction losses alone will be 230 watts.

If you instead use the IHW30N160R2 1600V IGBT for example, the voltage drop at 10 amps is ~1.4 volts at a junction temperature of 175 degrees, giving conduction losses of 14 watts. Switching losses will be somewhat higher than the MOSFET, but unless the frequency is extreme then the total losses will be way lower. Another bonus is that the IGBT is less than 1/4 of the price of the MOSFET.

jdub1581hv

Sat Nov 14 2015, 05:26AM

Registered Member #55219 Joined: Tue Jun 09 2015, 11:21PM
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Posts: 80

Well you could go this route.. STGWT28IH125DF
10 for $40 'aint to shabby..
Very stable and cool running in my ZVS and very large arcs at lower voltages

paris

Sat Nov 14 2015, 08:49AM

Registered Member #3042 Joined: Wed Jul 28 2010, 12:36AM
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Posts: 121

I ended up getting the 20N150 from mouser via local bussiness , not cheap
those 10 for $40 , on my screen is nz$71.30 :0(

GrantX

Sat Nov 14 2015, 12:58PM

Registered Member #4074 Joined: Mon Aug 29 2011, 06:58AM
Location: Australia
Posts: 335

paris wrote ...

I ended up getting the 20N150 from mouser via local bussiness , not cheap
those 10 for $40 , on my screen is nz$71.30 :0(

Is the switching frequency too high for IGBTs? I would imagine the heat dissipation in such a high resistance MOSFET would be annoying in a typical flyback circuit. A big heatsink and perhaps a fan would definitely help, and if the input is only a couple of amps it may not become an issue. I recently purchased some 1200V IGBTs which were very cheap compared to the equivalent MOSFETs.

paris

Sun Nov 15 2015, 09:20PM

Registered Member #3042 Joined: Wed Jul 28 2010, 12:36AM
Location:
Posts: 121

gonna use big heat sinks . freq up to 240khz

Id like to know which , and where you got IGBTs
OZ supplier?
Ive been aware of the "Fake parts" threads on here , gives me the willies

hen918

Sun Nov 15 2015, 10:49PM

Registered Member #11591 Joined: Wed Mar 20 2013, 08:20PM
Location: UK
Posts: 556

paris wrote ...

gonna use big heat sinks . freq up to 240khz
...

240kHz sounds too high for almost all IGBTs. The new SiC MOSFETs at 1200V should do well, even if they are a little expensive!

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