1
\$\begingroup\$

I was testing a SMPS (boost) where I had an overcurrent due to overload for a few seconds.

The inductor saturation current is 2A.

Although I could not measure the current, I am quite sure that the current was a few times higher than the saturation current.

I was able to switch off everything within a few seconds.

After that I removed the load and the converter works fine under no load.

However, when I connected a load which was previously working fine, the converter is not able to deliver the current and goes crazy.

Basically same behaviour as in the "failure/overcurrent" case.

I checked and inspected all the components, they look fine.

So based on this my hypothesis would be that the short "failure/overcurrent" has changed the inductor characteristics. In particular the saturation current has lowered.

I could not find any information online whether this is physically possible. Is there anyone who can shed some light on this?

(I am using a shielded SMD box inductor.)

BTW: Unfortunately, I don't have an LCR meter to measure the inductance.

\$\endgroup\$
  • 1
    \$\begingroup\$ Now would be the time to get one (an LCR meter). \$\endgroup\$ – Dave Tweed May 5 at 13:30
  • 1
    \$\begingroup\$ What makes you think it's the inductor? I would be more suspect of the controls/switches. \$\endgroup\$ – calcium3000 May 5 at 13:31
  • \$\begingroup\$ @DaveTweed :) I guess your right \$\endgroup\$ – Navaro May 5 at 13:34
  • 2
    \$\begingroup\$ I don't think that over-saturation will change the characteristics. Unless you overheated it enough to crack the core. Can you measure the current that is charging the inductor? Use a current probe, or put a small resistor in series with the MOSFET. The slope of the rising ramp should be Vs/L. If the inductor is saturating, the current will spike at the end of the ramp. \$\endgroup\$ – Mattman944 May 5 at 14:09
  • 1
    \$\begingroup\$ It's far more likely that you've damaged the MOSFET. It is possible to change the characteristics of a device (usually for the worse) without destroying it completely. \$\endgroup\$ – TimWescott May 5 at 15:33

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Browse other questions tagged or ask your own question.