Inverter H-Bridge Ringing

Thread Starter


Joined Jan 13, 2012

I am currently in the process of designing a 2kW generator.:)
However, I seem to be running into a couple of problems regarding ringing and MOSFETs blowing up.

For the spec of the design... It is running off an alternator. Depending on the spped of the alternator (depending on how much load is on the generator), the input voltage will range from 30V to 130V. I have no idea about these figures, as I was told that is what they would be.

I also got told to make the PIC run at 100kHz, as this will reduce the size of the transformer needed to step the 30V to 130V up to 375V.

The problem I am having is that there is ringing on all the lines that I am measuring throughout the circuit. I have attached a couple of screenshots from the scope when I was measuring it. I was measuring across the 3Ω Load. I am using this resistive load until I can get it working on a high voltage, then I will switch to the transformer.

Also, I blew up one side of the bridge at 100kHz, 36V. (Having to use batteries due to current limiting PSU). So I halved the frequency, just to get it working, and the ringing seemed to have decreased.

Long post, but just a question of... Am I doing this right? Are there any obvious mistakes I am making? And finally, with the slight ringing that is currently there, how do I get rid of it? Or is it acceptable?

Thanks for your time to read this post,




Joined Jul 9, 2011
Some ringing is normal. It doesn't look to bad.

1. What's the deadtime at max PWM width?
2. Many people experience problems with the 2110 when they tie COM and VSS together. (Like latching outputs for example) See if it's possible to use a separate power supply for the primary side.
3. 100kHz is high. You need to be sure that the switching components do not get too hot. Do they have heatsinks? Did you monitor their temperature?
4. The ringing depends on how fast the FETs are turned on and off. It can be decreased by adapting the snubbers (or using others) or by increasing Rgate, but this will also increase switching losses
5. VDSS of the IRFB4321 is 150V, quite near to the 130V bus voltage you want to use. Too near IMO. Use one with a higher VDSS.

Can you post a datasheet of the diode?

I forgot to say ringing is also heavily being influenced by your layout. If possible post a picture of your setup.
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