abc_de
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Due to cost point of I am using mosfet irf740Use IGBT's with the highest current rating you can get - put a fast fuse in line with each phase - check the dead time is 500nS under all conditions - make the turn on of the devices slow to limit RFI getting into the control
Sir I am not using bldc motor its acim motor not hall sensor no back emf etc.A BLDC inverter without a current sense is just a plain bad idea.
Especially at eg start up when there is no back emf on the motor coils.
FETs are very bad at breaking high currents...IGBTs are better.
But without current sense?...its like telling a car forum that you want to drive your car without engine oil.
Hi,
my guess (that´s all I can do with this little bit of information):
* bad PCB layout --> overvoltage spikes --> destroyed MOSFET isolation barrier --> shorted MOSFET.
* a current monitor will not avoid killing the MOSFETs
A schematic and a PCB layout would be helpful.
Klaus
100ohmWhat is Ron & Roff on the gate drive?
YesAre the mosfets properly heatsunk ?
180vdcAre there more than 400V at turn off? - across the mosfet's
110vac, 2ampwhat is the motor power?
180vwhat is the DC bus ? volts? max ?
everything working fine but mosfet below after few month of regular workingis the gate drive working properly ?
fast fuse only on dc bus +180vdcfast fuses in each motor line seems like a good idea at this stage .....
Due to space and cost no decoupling cap on each leg only 470uf/250vdc cap of dc bus--- Updated ---
you appear to have no film foil caps across the DC bus right by the mosfets ...? this is a very bad idea not to have any.
Actually I am following Germanyin India - if you get a surge on the rectified mains, plus the fact you have no local caps on the mosfets means that the odd blow up is to be expected - snubbers across the mosfets would be the only easy attempt at a cure ....
--- Updated ---
what value is C1, C9, etc? what bootstrap diode are you using? what is sw freq?
I have design it 1.5year ago right now I don't have documents.
Hi,
PCB layout: doesn't every PCB layout guideline say you need a solid GND plane?
... and fast capacitors?
MOSFET voltage at turn OFF:
Not even a perfect PCB layout will have zero overshot.
And "DC" surely is not correct here. At turn OFF there will be a peak, maybe very short. It's magnitude will vary with load, RPM and other factors.
To refine the question: What is the worst case peak voltage at turn OFF?
The PCB layout does not follow "power switching applicatiin" recommendations.
Please post the PCB layout guideline(s) you used and the demo board PCB layout you talked in post#3 so we can discuss the details.
I still am with my first guess from post#2.
Klaus
Ok I got your point may some points are missing due to lack to experience and shortage of time during design timeHi,
No documents? Makes no sense, nowadays. I've documents decades of years old. Internet will have, too.
Star connection may be good for low noise, no_current audio circuits.....but for high current switching ... sure you know what you are doing?
Copying boards without understanding of current loops, ground bounce, trace inductivity, ground planes, frequency range of capacitors....
Will result in non reliable design...the long term fail is no surprise.
My recommendation: a PCB redesign.
Klaus
OkHi,
There are plenty of good application notes and design notes. Read them.
Also in this forum there are many threads where I and others discussed exactly those problems.
Even with bad example layouts and their correction.
Klaus
Thanks for suggestionsHi,
I´ve already shared my knowledge. Just do a forum search. There are really detailled discussions.
I don´t think I/we need to repeat our knowledge for every member individually. This is not how a forum should work.
Reread post #13.
And read and refer to application notes / design notes. Do your job.
Just saying "I don´t have the documents anymore" is not showing any effort. All information is already available in the internet ... many thousand times.
Klaus
I just take the refrence of original pcb it's my own design in original pcb the drive mosfet by transistors and their design is 20year old.AT 1.5KhZ, you should be using IGBT'S ...
--- Updated ---
it appears you have copied a card imperfectly and used slightly different components, possibly lower quality ones, therein lies all the issues.
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