TOP259EN exploded

Hi Tugay,

Were you able to capture Vds waveforms at loading conditions below 600mA? Can you also provide information regarding your transformer (images, core, measured magnetizing inductance and leakage inductance). This will be helpful in finding the reason for failure. In addition, can you confirm that the polarity of the transformer windings is correct. Thanks

Hi PI-MazrimTaim,
I was not able to measure Vds waveforms at loading conditions because when ossiloscope was connected to vds, residual current relay triggered. at no load, I see 32v at the output voltage and 9v at the bias side.Doesn't this show that the polarity is correct?
Actually I don't know how to test Transformer( measuring magnetizing inductance and leakage inductance, etc )?
There are some information about transformer test on the PıExpert but I'm not sure I got it right.
I measured as follows,(I have used just LCR meter to measure)
*I shorted bias pins (4-5) and secondery pins (10-11). Than I measured primary side(pin 1-3) with LCR meter for leakage inductance.(LCR Meter setting is 100kHz).
*All pins are open. I measured primary side(pin 1-3) with LCR Meter for magnetization inductance. (LCR Meter setting is 100kHz).

1-) Is my measurement method correct?
2-) If It is not correct, how to test transformer correctly?

Thank you for your help.

Hi Tugay,

Yes you method of measuring is correct. The measured leakage inductance should be less than 1-2% of the magnetizing inductance. What values were you able to measure?

As for the voltage seen at no load, it is still possible for it to regulate even if the polarity of the transformer is incorrect. Assuming all components are properly selected, rated, and assembled, the best way to debug your design is thru waveforms especially the Vds. Try probing Vds usin a differential probe. If no differential probe is available, use a single passive probe. Note that the GND of an oscilloscope is the same for all channels so make sure to connect ALL ground clips in a single node. You can also choose to use only 1 GND clip.

Did you use a DER as reference for your design?

Hi PI-MazrimTaim,

I forgot to add something in the PI-Expert file I uploaded earlier. Now I added it. I used 23AWG wire right now because of I don't have any other wire sizes. When the 24AWG wire comes in I'll fix it but I think this issue not related to wire size.

I attach the measured values and winding directions of transformer. I used only LCR meter to measure.

1. The measurement in figure1 gives the value of leakage inductance, right?
2. Are Magnetization inductance and LP_nom the same thing ?
3. If they are not same, how to measure Magnetization inductance and LP_nom ?
4. Is the measured value in figure2 LP_nom or Magnetization inductance ?
5. Are directions of windings correct ? If they are not correct, can you describe it on the photo I took in which direction I should wrap with using colors?
6. Sorry, I could not understand what is the meaning "DER" ? Can you explain ?

I don't have differential probe, I ordered it but it will take a time to reach me. When it reach, I will measure.

Hi Tugay,

1) Yes.

2) Yes.

4) Lnom and Lmag are pratically the same.

5) I cannot comment on this since I am not aware of your schematic and layout design. Please wind with the dot convention in mind.

6) Design Example Report. It is a document we publish as a guide for designing using our products.

The inductance you measured is too high. It might be that you did not put and air gap in your transformer. For flyback, it is necessary to have an air gap to prevent core saturation. It is also used to get the desired inductance (Lnom)

Check out the PRODUCT DOCUMENTS tab in the link below. It has a list of DERs you can follow. 

https://www.power.com/products/topswitch/topswitch-hx/top259en

A differential probe is optional. You can use any passive probe as long as you use proper grounding when probing.