I had build an flyback converter based on UC3845 and some high voltage mosfet – it works fine, however I've got one problem with it. (but i'm not sure if that actually is a problem)
The core for the transformer I used is taken out from laptop power adapter (19V @ 3,5A). From what I reserached – this is RM10 core:
I'm getting 24V @ 2,5A from it, the transistor and secondary diode heats up, but has resonable temperature on the heatsink (40degC), However the transformer is getting quite hot (65-70degC) after some time.
This is the primary current of the transformer – it shows no saturation.
Is it normal for this size of core to get to those temperatures at those powers? If not – What is causing the excessive heating?
EDIT:
Here is the schematic:
And there is the secondary waveform at rated power (24V @ 2,5A):
Best Answer
That is a pretty reasonable temperature to run at. In fact I'd say it's probably running cool compared to most flyback designs. If you generally look at ferrite data sheets they state how much the temperature will rise under certain conditions. I've just answered this question on a similar subject and, I'll use some of that information: -
What the above is telling you is that if the peak flux density in the core is 100 mT and you are switching at 100 kHz, that core-set will dissipate 9.5 watts and rise in temperature by 100 °C. It's a recommended limit value so it's not advisable to run at this level (unless you know what you are doing).
That's fine!