Hi,
Can you share the schematic?
Have you tried building lower voltage, lower power versions?
Regards,
Jay_Diddy_B
![](http://www.smps.us/mosfet_inverter.png)
It is almost exactly this, just omit Q3 and D1 and the gate pull up resistors have a separate low voltage supply.
Yes, I initially tested a version using a 30V DC supply and a higher turns ratio, with a consequently higher frequency variation. It used a different core, a Ferroxcube UR42/21/12-3C8 with a very small air gap, as I had it handy. I got the EPCOS core because it was available on mouser with all the associated hardware and in various gap sizes.
You neglected to mention the total power level. Is this 10W or 1kW??
What part of what things are getting to 70C? Is that spot heating, or is everything thrown in an enclosure and it's the air inside heating up?
The magnetic field divergence is exceptionally intense near the air gap; turns near the center of the bobbin experience extreme eddy currents, even of very fine wire. Accordingly, layers at different heights will experience slightly different voltages; layers connected in parallel won't work as well as good old Litz, which is the best approach for high-ripple, high-Q inductors.
Tim
The target power delivered to the load is around 75W continuous in the worst case. These measurements were taken without a secondary (no load). I measured the core temperature by placing a thermocouple in the unused winding window, far from the middle of the center-post. The transformer is becoming uniformly hot and is placed open-air on my bench.
I am going to try using an appropriate guage litz wire, and also try increasing the gap size and turns to reduce the flux density. I too am suspecting the fringing field near the gap. I can detect 1-2% increase in power consumption just by placing the thermocouple near the gap. Would a distributed gap help in this case?
When I get home, I'll post the math I am using to predict the core losses, and maybe someone can point out an error, assumption, or omission that I am making. I would really like to be able to design on paper and build something that performs reasonably close to specifications the first iteration. This is my first foray into actual magnetics design, and a lot has already been demystified for me.