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LNK420 failure - cracks in the body what can I do?

Posted by: Evgen on

When we use LNK420 with power supply 75 W we have got cracks in the body. The photos are attached. Does it happen often with LNK420? What is the solution?

Comments

Submitted by PI-Crumb on 03/06/2017

This is unusual. Can you provide more info about the test conditions? Is the failure repeatable on all parts tested?

I apologize. I will be brief, i will clarify the situation.

This is not regular. At the moment is sporadic failure. It was noticed to me that this failure occurs duren transient processes:

- cyclic switch on/off power supply

- powerfull surge transients (this it indicated by a destroyed varistor, Y2 capasitor and fuse)

So, i`m inclined to think that the engineer made a lot of mistakes when developing a power supply:

- PCB. Design is bad. Does not even meet your recomendation. Reality, is not possible to obtain power above 45 watts, system is not stable. The situation is corrected by adding С18?

- BOM. No logic. 100V shottky diode (VS-12CWQ10FN), under doubt transformer configuration (ETD29 0,7mm gap N87 Pri: 81T Sec: 20T Bias: 13T), clamp network (1.5KE250), wide range of regulation current (30V 45-75W), C18 in parallel FB pin (Kirchhoff`s circuiit laws ?)

- As a result we have: low PF (about 0.9), unstable current regulation (more 5%), switch off PS if input voltage under 175 VAC (OVP triger), flickering 30-50% 

Files of project attached. This design copy of RDR-290.

Attachment Size
PCB_Bot.JPG 383.14 KB
PCB_Top.JPG 311.1 KB
Shematic.JPG 214.97 KB