Ferrite noise - screech

[Serge66]

Hi Guys,

I was wondering what make the ferrite transformer screech?
You know, that particular ferrite awful noise. A bit like fingernails across a black board.

Normally, that happens just before the transistors blow up.

Saturation of the core?
Thanks

Serge

[luka]

Hi

What you hear is probably high freq, because core is saturating, use bigger core, or a bit higher freq., or more turns on primary. That sound can be generated by winding too if windings aren't wind onto core tightly...

[Serge66]

Thanks Luka

[Serge66]

I am using ETD44. With EF90 cores. Good up to 200kHz.
Frequency is between 100kHz and 200kHz (resonant system with ST Microelectronics L6599 controller).
Primary turns is 23.
Secondary turns 46. I want 350V dc.
Resonant series capacitor is 22nF.
Resonant frequency is 150kHz.
Leakage inductance measured as 50uH (micro henries)
I think the primary inductance is around 2.3mH.

It works ok with 60V on the Xformer. I think I know why it blew up yesterday.
I have to test it again with 320V dc. Flak jacket, safety gear...and switch it on, baby.

Thanks

Serge

[luka]

Hi

But with 100kHz or more wires resonate so fast even if loosened, that you can't even hear then, at least not from switching... You will hear core make noise only if it is satureted, this also means it has to be loaded, not idle

Resonant converter are a bit harder to make, since you have to know some thing as you seem to know about trafo

Good luck, post some pic will you...

[Eva]

The noise is produced both by transformer saturation and control loop instability (wildly changing duty cycle or operating frequency).

[Serge66]

Thanks Eva.
Make sense, as I was not using a power supply middle point (i.e. two caps in series with balancing resistors). One end of the xformer is connected to the transistors middle point (half-bridge) the other was to the negative rail. This applies 330V plus to one transistor. The xformer is calculated with +/- 170V.
The transistors I use now are only rated at 400V. Soooo 330V plus noise and spikes is not good for their health.

I will try again with middle point.

Serge

[sss]

soak the core with the windings into special varnish for trasformers , or into some high temp epoxy .

[jamesrnz]

i had a similar problem with noise and then later fire and smoke and plasma bursts as i increased the current/load on a power supply i am working on building.

well after much time and transistors i discovered i have been using a ferrite toroid for the inductor. ft-240 of 77 material...

so i ordered some iron core ft-240 8 and 23 material toriod cores.

i have been on the road for a couple of months and my wife told me they arrived.



SO....I thought I would wind it with 30 wires of 26 gauge .

BUT..... I read that litz type wire is unnecessary.

SO........ one solid wire or multi-wire-enameled? for the inductor...............

[Eva]

Litz wire is hardly required for SMPS output toroid inductors. Go with solid wire.