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From: "Peter Larsson"
Subject: MOSFET losses,CUK converter !
Date: Mon, 30 Sep 2002 11:32:15 +0200
NNTP-Posting-Date: Mon, 30 Sep 2002 09:35:03 +0000 (UTC)
X-Newsreader: Microsoft Outlook Express 6.00.2600.0000
Hello I have tried to build an CUK converter.
The converter has an IRFP 250 transistor and three ETD44 (overkill, but this
is only for my own test) cores with C85 material.There is a small
airgap(outer legs too) ~0.4mm on the first coil and it is wound with 10
Electrolytic capacitors 2x680uF low ERS made for up to 100kHz on primary
side parallelled with 100nF polyprop cap.
The transformer is wound with 3 turns on primary side and 10 on
secondary.(Litz wire 90 strands in one bundle).
Electrolytic capacitors 1x680uF low ERS made for up to 100kHz on secondary
A fast diode is used on the secondary side.
Output core has no aigap and is wound with 10 turns.
Drive circuitry for the MOSFET is an elantec driver with rise and fall time
about 30 ns (measured).
Used frequency: 100kHz
The converter is made to do this:
12 to 30 volt conversion with max 5 amps at 30 volt from a 12V car battery.
Problem: transistor IRFP 250 is running too hot when i load with 5 ohm, when
i load with 10 ohm it is not too hot.
This converter only have about 50W as output but should easy handle 150W.
I have measured the current into my application with a small resistor and
here I can see that the first core is not in saturation.
Is there an easy way to measure where the problem(s) are ??
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