Heat Solution for Closed Enclosure Design

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I am working on Lytswitch-5 base isolated design using 5216D. Circuit works properly with open enclosure. But when I mount in closed enclosure within 12 minutes it gets too much heat and gradully current decreases and then it shutdown. IC blown out by its Drain and source gets shorting when this problem occurs. 

o/p voltage : 54V, 

o/p Current : 290mA

Transformer Geometry : EE16

I request you to guide me to solve this problem.

Sir please give feedback for said problem. I am stuck on my design so production is stopped due to this problem. I had already purchased the material. Please support.


LYT-5 has built-in OTP so it is very unusual for the IC to get damaged. Are there other devices that get damaged? It could be other parts that got over-stressed like the output diode or transformer saturation. Please make sure that there is no saturation at high-temp.


I have tested 3 more prototypes but same issue is obeserved. It is found that LYT5216D, EE16 and Output diode is heat too much. Suggested op diode was ES3G, but used was UF5408. apart from that all the componets are as per design. It is also takn care that as per spreadsheet parameter core saturation does not occur. Kindly help to solve out this problem.

Can you confirm there is no core saturation by monitoring the drain current? Also make sure that the transformer does not have excessive leakage. You can try to use sandwich winding to reduce the leakage if necessary, in which you split the primary and put the secondary windings in between the primary windings.

How about the primary clamp? The device rating of LYT5226 is only 650V. Exceeding this value could damage the device. Is it possible that this is what happened? Please make sure that the breakdown voltage is not exceeded.

If the waveforms look normal, then the ambient temp is maybe just too high that requires more heatsinking. Still, the IC should not get damage unless it exceeded its rating so hopefully it's just a matter of optimizing the components.


You may check DER-528 as reference for an isolated design.