Inductor core saturation

francis29 · Mar 22, 2016

I am currently working on a boost converter.
the current waveform i am getting is this(of inductor).
It has no similarity with theoritical waveform.
My doubt is the core is getting saturated.
can anyone have an idea what could be the reason??

betwixt · Mar 22, 2016

Please try attaching the waveform image again.

Brian.

francis29 · Mar 22, 2016

this is the current waveform i am getting from tektronix current probe.

treez · Mar 22, 2016

sometimes the powdered iron type cores get less inductance as the current gets higher, making it look like theyve saturated when they havent.

Warpspeed · Mar 22, 2016

We really need to see the current waveform, and please tell us what the core material is.

FvM · Mar 22, 2016

Need to look at the schematic. It's not possible to distinguish core saturation and possible switch current limiting by only looking at the waveform. Also the current polarity should be clarified. If it's a DC current probe, we won't expect saturation near zero current.

francis29 · Mar 22, 2016

It is ac/dc current probe.

FvM · Mar 22, 2016

Then it doesn't look like saturation. Show the circuit, clarify what's on and off phase in the waveform.

francis29 · Mar 22, 2016

Actually its switching node waveform across mosfet.
this is the schematic

Warpspeed · Mar 22, 2016

The two waveforms do not seem to correspond in time.
Something appears terribly wrong with the test set up.

The current waveform looks to be delayed, as well as frequency limited.

treez · Mar 22, 2016

francis29 are you using an schottky diode, or at least an ultra fast diode in that boost?

- - - Updated - - -

Also, what is your intended F(sw), vin and vout?

francis29 · Mar 23, 2016

Diode is rurg3060
vin 50
vo 110
f 20Khz

mtwieg · Mar 23, 2016

The switch node looks okay (though it looks like less than 100V on the output). I suspect there's something wrong with the current probe itself. Are you sure it has enough bandwidth?

treez · Mar 23, 2016

also is there an enormous snubber across the diode and/or fet?

francis29 · Mar 23, 2016

I changed the inductor. now i am getting correct waveform. thank you guys.
so the problem was core saturation

And one more problem i am facing is about voltage spikes.
across mosfet working voltage is 110v but i am getting around 300V voltage spikes. is it okey to leave it as it is or i have to go for a snubber?
the mosfet is rated 650v.

treez · Mar 23, 2016

Here is pcb layout document which you must satisfy b4 looking into snubbers.
If you can pass emc though, and you dont overvoltage anything with the ringing, then doesnt matter about ringing too much, just leave it.

mtwieg · Mar 23, 2016

francis29 said:
I changed the inductor. now i am getting correct waveform. thank you guys.
so the problem was core saturation

There was definitely something other than core saturation happening. Saturation can't cause the lagging waveforms you showed.

And one more problem i am facing is about voltage spikes.
across mosfet working voltage is 110v but i am getting around 300V voltage spikes. is it okey to leave it as it is or i have to go for a snubber?
the mosfet is rated 650v.

The FET should be okay, though you should also make sure the negative spikes aren't going to exceed the voltage rating of the diode. But even if the power components can withstand the spikes, they will likely cause large amounts of emi in the rest of the system, so they should be tamed. Try optimizing your layout to reduce parasitic inductance, and then add a snubber.

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