Problem with SMPS design for high power ultrasonic

[Ioannis]

It may be bad ground, no decoupling capacitor on power lines.

If you use a E-I transformenr,a little gap may help avoid saturation. Put a thin paper in between.

HTH,
Ioannis

[George]

Thx - I'll try gapping the ferrite core a little - one thing I cant get my brain around tho is: How come a slight imbalance in drive can cause the core to saturate when push pulling, but it's ok to just switch DC pulses through a transformer and only drive it in one direction without it saturating?

[George]

I've found this in the data sheets - my core is N97 operating at 25kHz tho the data sheet says:

"Large E/ETD, RM/PM cores made of N27, N97, N87 (with large core cross sections (Ae ≥250 mm2), on account of eddy-current losses N87 must be used even where f <100 kHz)"

Is this likely to be my problem? I cannot find an N87 core in my transformer size. Is it worth me getting a different size bobbin and starting from scratch?

Gapping and decoupling didnt seem to help much, is the topology with half bridge suppling one side of transformer and a capacitive divider on the other (as attached) likely to be easier for me to accomplish successfully?

[Ioannis]

Do you have any means to compare the two transistors used in the circuit?

The idea of two capacitors as voltage divider in my opinion is very bad.

In general I avoid this kind of circuits, as the parts should be identical (as much as possible).

Sorry I cannot help any more.

Ioannis