top 249 power supply diode problem

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I designed a power supply with top249. I m sending the schematic of design. its 26V 2.1A. but its works 3 minutes then the output diode is burning. this diode name is Do. I have no UF5404 so, I m using UF5406. But its values is higher then UF5404. What is the reason of that diode's burning?

I designed a power supply with top 246 . its 40V 1A and 32V 0.4A . but its works about 20 minutes then the output diode is burning .Both output diods are  uf4007.I replaced by uf5408 . but those are very hot. please help me.

Power loss on the diode is around 1.8W. You may have to use bigger package part or use  heatsink to solve the thermal iisue. Voltage stress of the diode at both steady state and power up need to be checked too. For a reliable design, the maximum voltage stress over any conditions should be less than the maximum voltage rating of the diode.

please help me.

The diode can be failing for 3 reasons.

Exceeding current specifications

Exceeding maximum reverse voltage.

It is getting too warm 

You need to review your design and check for the current and voltage trough the diode when the supply is running at full load and minimum input voltage. One thing I know by experience is tha If you have a 3 amps rated diode and you are loading your power supply with 2.1 amps, then you need somehow to remove the heart from the diode.


What I would do if I were you is to measure the voltage and current you are having trough the diode. This is for make sure your power supply is properly working.   IF the supply is working as expected then I would change the diode for a Schottky rectifier.   It has a lover voltage drop so it will dissipate less heat.  Also, for the 2.1 Ams output, I will use a diode with at least 4 amps rated specs.