By all accounts - the MOSFET has been replaced on a number of previous occasions.

Its entirely possible that the entirely random first failure involved a LL MOSFET, and subsequent replacements were not LL.

But that's my point.
My understanding was that all replacements were a BTS240, which is a non-LL MOSFET.
It would seem prudent to replace that with a logic-level device.

 

The bts240a is same as original. The Compagny have allways be haunted by the burning bts240a. But due to hard competition the compagny at last must close .
I need a different one to eleminate this fault
Yesterday we change the k7a and k7b to check if the many change a relay do can wear it. and be the cause also or if the hole circuit has been misdesigned from beginnig

 

Can't see in datasheet that bts240a need 10v to fully open.
And all your cleaver people must have a suitable replacement

I am not that cleaver into MOSFET

 

Can't see in datasheet that bts240a need 10v to fully open.

To me "open" is off. A Vgs of 10V turns the MOSFET ON.

Look in this data sheet at the Vgs used where the Drain-source on-state resistance is specified.

A quick search turned up the STP80NF55L-06 as a replacement, which has an ON resistance of 8mΩ @ Vgs=5V, < half of the BTS 240A at Vgs =10V.
Other similar devices are likely available.

 

Found same on this page where i shop
http://dk.farnell.com/stmicroelectronics/stp80nf55l-06/mosfet-n-to-220/dp/1291989

But they say 10v ??!!

 

I know this is asking a lot but look at the technical data sheet.
Rds is tested at both Vgs=5V and Vgs=10V.
The only difference is the Rds(on) is slightly higher at 5V.

 

But that's my point.
My understanding was that all replacements were a BTS240, which is a non-LL MOSFET.
It would seem prudent to replace that with a logic-level device.

Sometimes a LL MOSFET will have a "L" suffix appended on an otherwise common part number - something that's easily missed by some.

 

Sometimes a LL MOSFET will have a "L" suffix appended on an otherwise common part number - something that's easily missed by some.

That's good to know.
I see that the replacement I suggested does have an "L" suffix, so that's in line with your observation.

 

That's good to know.
I see that the replacement I suggested does have an "L" suffix, so that's in line with your observation.

It varies with make - but I think the "L" suffix is more common.

 

The replacement part have now been working for a month without any problems,
Lets hope it keeps on working

 

The replacement part have now been working for a month without any problems,
Lets hope it keeps on working

Did you use the device I suggested?

 

http://dk.farnell.com/webapp/wcs/st...estType=Base&partNumber=1291989&storeId=10157

 

Did you use the device I suggested?

I think he meant "YES".

Allen