MOSFET protection (inductive load)

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What's the best way to protect the power MOSFETs from a H-bridge circuit with an inductive load (a low frequency transformer)? That's the output stage of a sine wave inverter (2kW).

The MOSFETs randomly blow out even with small loads. The MOSFETs are rated for 60V/280A and the H-Bridge rail voltage is 28V (two lead acid batteries).

Most probably the problem is the ringing coming from the switched primary winding of the transformer. Do I need a snubber circuit for each MOSFET or do I need a different kind of suppression circuit?

I've read somewhere about TVS diodes and there was a suggestion to put one between DS terminals (5kW/35V rated) and one between GS terminals (300W/16V). Is it enough?
 



yes i have this problem too
i have IGBT and i want to calculat sutable R and C for it but i cant
can anybody help????
 

Hi,

show your schematic.

Usually with a mosfet full bridge you don´t need extra protection, because the mosfet built in body diodes do this.

Most probably it is a layout or a schematic problem, like loosing capacitors or stray inductance.


Klaus
 


I send pic of schematic to you
I have one IGBT that switch with 2kHZ and put high voltage (about 250 or 300 volt) to selonoid
I put R and C snubber but i cant calculate the value of them

 
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350uF seems like an extremely large value. Use values between 1uF to 10uF. Additionally, you may add a diode in parallel with the resistor for enhanced snubber performance.
 
mrinalmani said:
350uF seems like an extremely large value. Use values between 1uF to 10uF. Additionally, you may add a diode in parallel with the resistor for enhanced snubber performance.
Click to expand...

the value that i write is not important and it is sample...
what is proper value for R?
and do you think it is better to use mosFET insted of IGBT? i think mosfet is faster than IGBT in swithing
what is your idea?

mrinalmani said:
Have you ensured an appropriate dead band between toggling of switches?
Click to expand...

how can I find sutable band?
you mean the dellay in switch on and of?
time rise and time fall?
 
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MOSFET or IGBT depends upon the switching speed and power requirements.
Appropriate value of resistor is that which would limit the maximum discharge current of the capacitor within the pulse handling capability of the IGBT. So it depends upon the voltage across the IGBT and the pulse current that it can handle.

Dead band means a small delay between switching ON of one switch and switching OFF of another. (100ns is a typical value for MOSFETs, for IGBTs 250ns should be ok)
 

ok i get it
do you have perctical article? PDF or some thing....
i want to read more deeply about this topic
 

Hi,

Your schematic shows no H-bridge. Here you need protection.

You may use the diode directely at the load. And another one directely connected at the Fet to supply voltage, but use a fast capacitor to stabilize voltage caused by the current spikes. It needs a very short and solid connection to the fet's source.

Also don't use the led in the fet's gate circuit. Place it elsewhere.

Klaus
 



if i want to design H bridge , do you have sugestion?
how can design this circute with H bridge?
 

This circuit does not require an H-bridge. I was speaking of a bridge because the thread starter had mentioned about it. (Read post #1)
Find out more about snubbers in the attachment below
 

Attachments

  • Snubber_Circuits.pdf
    75.7 KB · Views: 1,563
  • snubber-TI.pdf
    1.9 MB · Views: 170
Hi,


i´m a bit confused, now i see this is because of hitch-hiking the original thread....

@javadgodling: Next time please start your own thread. Thanks.

Klaus
 

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