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Electronics => Repair => Topic started by: k.valentino on November 04, 2018, 06:36:47 pm

Title: Replace N-Channel MOSFETs
Post by: k.valentino on November 04, 2018, 06:36:47 pm
Hi  :) ,
need alternative to replace 3x N-Channel MOSFETs SUM110N10-09 – https://www.vishay.com/docs/70677/sum110n1.pdf (https://www.vishay.com/docs/70677/sum110n1.pdf)
Is it ok to replace with STB120NF10T4? – http://www.farnell.com/datasheets/1817542.pdf (http://www.farnell.com/datasheets/1817542.pdf)
Title: Re: Replace N-Channel MOSFETs
Post by: boB on November 04, 2018, 06:41:08 pm

Specs are very similar.  Very close.

I would think it would be fine to replace with for most applications.

Why does it need replacing ?
Title: Re: Replace N-Channel MOSFETs
Post by: k.valentino on November 04, 2018, 08:12:14 pm

Specs are very similar.  Very close.

I would think it would be fine to replace with for most applications.

Why does it need replacing ?

I see the difference in the power dissipation. Maximum Power Dissipation (T=25°C) is 375W vs 312W .But I don't know if it will importance.
I have faulty brake resistor controller with 3 blown transistors - the photo
Title: Re: Replace N-Channel MOSFETs
Post by: coromonadalix on November 05, 2018, 01:38:19 am
Is this a drill brake controller ?   wow  its was a big  pooof

The important stuff in the mosfets are the rds values,  internal "resistance drain source"  in ohms value and sometimes the capacitance,  the dissipated values are near match, i think it would fit.

The problem is the tab is completly soldered, you will have to solder it pretty fast with a stong iron, use solder wick to remove completly the solder,  tack the 3 pins on the pcb, preventing it from moving, and apply gentle pressure to be sure the mosfet has no clearance under it ans solder it fast as i said. Use flux to help ?
Title: Re: Replace N-Channel MOSFETs
Post by: T3sl4co1l on November 05, 2018, 02:42:09 am
Soldering is no problem, just melt and bend the leads up, then dump heat into the tab until it lifts off.  Tin and wick the pads clean, then solder down the replacement.

I'd be more worried that:
1. You haven't addressed the root cause, so it's likely to blow again,
2. That looks like it used to be a potted module.  In other words, "you poor SOB..."

...Fixing a potted module, while absolutely possible, is on the "heroic" side of repairs.  Are you sure you can't actually find/buy a replacement, considering all the time and materials you'll spend on this repair?  Almost always, such repairs are "penny wise and pound foolish".

And when you're done, you have to pot it back up, which means expensive silicone (by the looks of it) resin, and maybe a vacuum chamber to be sure.  Otherwise it's just going to fail again, some time later, and much worse, due to whatever environmental contamination they were potting the thing against in the first place.

Tim
Title: Re: Replace N-Channel MOSFETs
Post by: k.valentino on November 05, 2018, 09:39:38 am
I think will not have any problem with soldering the transistors.
It is worth repairing the module because buying another one costs about 100€
Thanks for help me!
Title: Re: Replace N-Channel MOSFETs
Post by: wraper on November 05, 2018, 09:44:20 am
I see the difference in the power dissipation. Maximum Power Dissipation (T=25°C) is 375W vs 312W .But I don't know if it will importance.
Considering they are not even on a heatsink this figure does not matter.
Title: Re: Replace N-Channel MOSFETs
Post by: coromonadalix on November 05, 2018, 11:20:03 am
The pcb copper layer is the heatsink
Title: Re: Replace N-Channel MOSFETs
Post by: wraper on November 05, 2018, 11:34:48 am
The pcb copper layer is the heatsink
And how much can it dissipate? A few W?

Quote
Thermal resistance junction-pcb max 35 °C/W

1. When mounted on 1inch² FR-4 board, 2 oz Cu
Title: Re: Replace N-Channel MOSFETs
Post by: boB on November 05, 2018, 05:18:40 pm

Also, don't forget to at least measure the gate resistor to make sure it is still a resistor.  It should be a fairly low value, probably under 100 Ohms or so.

Replace it too if needed and if you can find it under that potting material !

Title: Re: Replace N-Channel MOSFETs
Post by: k.valentino on November 05, 2018, 09:26:48 pm

Also, don't forget to at least measure the gate resistor to make sure it is still a resistor.  It should be a fairly low value, probably under 100 Ohms or so.

Replace it too if needed and if you can find it under that potting material !
the resistors are fine - they are 10 Ohms