LNK419 - Clamp Diode Heating Up

2 posts / 0 new



I am going to make 20W (31.2V, 600mA) Isolated LED Driver. But My Clamp Dioded is overheating and after some time LNK419 blows up.

I have attached my basic circuit design as image file.


I have done following things to solve this issue

1) Used three different Transformers but failed. (RM8, EE25, EE30)
2) Changed Bias Resigter R3 (10ohms to 255 ohms)

3) Chaged Bias Diode D4 (1N4148, ES2D, 1N4935)
4) Changed D3 Diode (UF4007, ES2D)


Tell me all possible reasons for overheating of Clamp Zener Diode.

Please use PIXLS Designer 8 software on your design and make sure that the transformer design does not exceed the maximum flux density or it will saturate. This could be one reason why the clamp is overheating and the LNK419 blows up.

Please also check that the output diode you use does not exceed PIVS in the spreadsheet.

There is also one item in the design spreadsheet called PCLAMP which should give you an estimatte of how much power dissipation you expect on the clamp. You may need to put two zener in series or use higher power zener.

But first thing first, please monitor the drain voltage and current and check for abnormal waveforms like current saturation.