Crackling transformer

[engineer1000]

I have a half bridge made up of two IGBTs switching at approx 30khz. The half bridge is powered by rectifed mains so approx 325Vdc across bridge. A transformer is fitted across the half bridge . The output of the transformer has a scope lead across it. When I turn on the bridge I get a square wave out, but its a bit jittery and the transformer crackles.
I have a module that switches the IGBTs on and off with a dead time of 2us.
I want to know what causes the transformer to crackle.
The same transformer has been used on a similar cct and seems to work fine so I don't think it's the transformer
Can anyone help?

 

[jiripolivka]

I have a half bridge made up of two IGBTs switching at approx 30khz. The half bridge is powered by rectifed mains so approx 325Vdc across bridge. A transformer is fitted across the half bridge . The output of the transformer has a scope lead across it. When I turn on the bridge I get a square wave out, but its a bit jittery and the transformer crackles.
I have a module that switches the IGBTs on and off with a dead time of 2us.
I want to know what causes the transformer to crackle.
The same transformer has been used on a similar cct and seems to work fine so I don't think it's the transformer
Can anyone help?

The cause is magnetostriction. Many ferrite cores change their dimensions close to magnetic saturation and with pulsed current one can hear crackling sound.
In principle the crackling is not a problem. If you need, use potting in wax or resin to attenuate the sound, only make sure the heat dissipation is not affected.

 

[Rik797]

Hi all,

I'm facing a similar issue.
I employ a ferrite-core transformer as output transformer to obtain galvanic separation in a SMPS.
My output voltage is discontinuous (e.g. 0.5 secs on, 1.5 secs off). When the circuit starts conducting (e.g. at the beginning of the 0.5 secs) the transformer makes a 'click' (as your mouse button does :wink.
May that be normal?

Cheers,

Rik

 

[jiripolivka]

Hi all,

I'm facing a similar issue.
I employ a ferrite-core transformer as output transformer to obtain galvanic separation in a SMPS.
My output voltage is discontinuous (e.g. 0.5 secs on, 1.5 secs off). When the circuit starts conducting (e.g. at the beginning of the 0.5 secs) the transformer makes a 'click' (as your mouse button does :wink.
May that be normal?

Cheers,

Rik

This effect is due to magnetostriction,or material dilatation due to magnetization. Ferrite cores are known for it for many years since they started to be used in TV flyback transformers. Certain ultrasonic generators utilize magnetostrictive ferrites to generate waves in water, etc.

 

[FvM]

When I turn on the bridge I get a square wave out, but its a bit jittery and the transformer crackles.

Might be due to an unstable control loop, or if the inverter is operated without feedback, an unstable oscillator circuit. Less likely a problem with a power electronic component.

The cause is magnetostriction.

Yes, but you won't hear a sound from a stable and continuously operated inverter.

 

[Rik797]

This effect is due to magnetostriction,or material dilatation due to magnetization.

Okay, but can a noisy magnetostriction be harmful in ferrite transformers?

 

[jiripolivka]

Okay, but can a noisy magnetostriction be harmful in ferrite transformers?

Until you break the ferrite, I think not.
By a clever design in DC/DC converters, the transformer is driven for the best efficiency without over-magnetizing the core which in turn reduces the efficiency.