 MOSFET snubber question
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Thomas F
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Sat Apr 14 2012, 09:26PM
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Registered Member #503
Joined: Sun Nov 19 2006, 06:37PM
Location:
Posts: 59
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Hello ,
I have a modified sine wave inverter (basically square wave with some deadband between the pos. and neg. halves).It is someone else's design and the problem is that it blows out the MOSFETs ,even when it starts up with no load connected.And sometimes it works OK.
The power source is a battery bank of 72V (which will be modified to a 48V subsequently). The inverter is rated for 7.5H.P. and will work for about 2 mins. max. have seen some other make units work perfectly without blowing MOSFETs.
I am trying to understand the issue.Most of the appnotes I have found on the net pertain to Flyback topologies. Is the snubber design completely different from the push pull center tapped version that I have in this inverter ?
I could post the schematic which I have traced if someone should care to have a look.
Cheers
Thomas
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IamSmooth
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Registered Member #190
Joined: Fri Feb 17 2006, 12:00AM
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Posts: 1567
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post your schematic here for everyone to see
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Thomas F
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Registered Member #503
Joined: Sun Nov 19 2006, 06:37PM
Location:
Posts: 59
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Hi thanks for the reply.
A few points :
1)The current sensing part has not been connected to the micro even though it has been shown.
2)The output is a 415V square wave,which is fed to a var. freq. drive which then powers a 5HP/7.5HP motor @ 8Hz in a slow speed application.
3)There is another auxiliary winding at the secondary,which is used to feed back the voltage to the voltage at SL5 which is then used to keep the voltage at a constant level.
The snubber design does not seem to make any meaning.As I mentioned the MOSFETs blow even when there is no load connected.
]ard_orig.pdf[/file]
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