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SMPS with TOP247 Kaschke transformer problem

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Junior Member level 1
Jul 28, 2007
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kaschke transformer topswitch

Hi! I'm currently trying to make this SMPS work properly. The problem is that the SMPS doesn't hold on load. It's expected to be 27-30V/3,2A 96W. Everything is fine until load >20W is reached. Then TOP-switch heats up and I think thermal shutdown occurs (actually not so sure,because on the scope pulses are getting smaller in amplitude,but not disappearing completely). TOP-switch is mounted on proper heatsink, but the heatsink is not very warm (45-50 C),because TOP-switch shutdown occurs in seconds after load is applied. I'm using PCB design and schematic exactly from PI application notes for this device. The feedback consists of optocoupler PC817A and zener diode. Snubber - BYW26C and P6KE200. ~220V input - common mode choke ,10A bridge rectifier,100uF/400V capacitor. Output - Schottky Diode 10A/200V ,1500uf capacitor. Transformer - Kaschke TRFSP-E36/11 067.039 .

**broken link removed**

The Datasheet is a little bit confusing. There are two secondary windings 15V/4,5A ? In parallel :?: Looking at the pinout of the transformer it's visible that these windings are not provided for in-series connection. So, I'm in a big doubt whether I'm using a wrong transformer. It's intended to be used specially for TOP247. One more thing - the secondary windings' start/end appear to be marked in opposite. If I connect them according to datasheet info - SMPS is "clicking" - it's in autorestart mode /1 click per second/. Looking at the scope is visible that transformer's energy won't dissipate due to the opposite connected winding. Primary and Bias windings are OK. Now I'm testing it using only one of the secondary windings. And lastly - Primary Inductance is 178uH - isn't this too small ? Any ideas and opinions are appreciated ! Thanks !

kaschke transformateur

The 067.039 datasheet shows a single 15V/4.5A secondary winding. I don't know, if the datasheet is corresponding to your part, but I see no unclear points in the datasheet. There's probably incorrect information about the part in an overview catalog, that tells about dual secondary.

dual secondaries transformer only using one

Thanks FvM ! Transformer is marked 067.039. So, it's the same,I've ordered. You are right about the overview catalogs. In one of them this transformer was noted to be a single secondary 27-30V/3,2A,in other - a double secondary 27-30V. I've examined several overview catalogs,from different years and places and all of them state that secondary is 27-30V (single or double). I can't believe that if there is a mistake,Kaschke hasn't eliminated it. This part has been on market for years.
The transformer has two secondary windings indeed. But why in the datasheet is stated ,as you say,a single one? And why 15V? And what about transformation ratios - 1:0,266:0,6:1 - aren't they too low, promting that secondary winding should be a higher voltage one,not 15V :?:

topswitch with kaschke transformer


some of PI PI application notes not working very well..i hvae the same problems with the TOP247 before..many TOP blow's up..
U can setup the OutPut power with two resistors at the TOP.u check this first..but be carefull with this..the transformer can be saturation and the TOP can't switch-off fast..this the problems of the TOP-switch...
for check ur problem i need ur layout and schematic..and the BOM


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