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K2837 Mosfet, replacement for use in multiprocess welder

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neal.iweb

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For a multiprocess welder, I cannot find compatible replacement mosfet and their resistor parts. Of the (12) twelve K2837 mosfets and the (12) twelve 1.9 ohm 1/4W +/-0.25 tolerance resistors across them, the board fried 2 mosfets and the 2 resistors across them. Two problems… Can anyone please confirm the actual and correct specification datasheet for the K2837? 1.9 ohm resistors are not available anywhere that I have looked. I want to replace all 12 mosfets and the 12 resistors that would match the 12 mosfets. The datasheets for those K2837 that I have found – provide contradictory info. Several show the part as being the same specs as for the 2SK2837, but were labeled for the K2837. Other ones show specs with higher values across several specs for the K2837. I do not know what specs I should be shopping around for.

At this point, if I use the higher specs that do not match the 2Sk2837 mosfet, then the suitable replacement mosfet for the K2837 is part number FQA24N50. Can anyone confirm this or provide a compatible mosfet for my welder? Please tell me if the following are minor differences and if the FQA is the replacement that I need.

The differences in the two mosfet’s datasheets I found are:
  • The K2837 has Derating Factor above 25C at 2.22W/C and the FQA is at 2.33W/C. As a reminder, the current Upper Board has 1.9 ohm resistors.
  • the K2837 has Power Dissipation of 271W and the FQA24N50 has Power Dissipation of 290W.
  • The Thermal Characteristics, are that the 2837 has .46C/W, and the FQA has .43C/W
  • The Static Drain Source On-Resistance on the K2837 is showing “Typical” as .16 ohms, versus FQA as 0.156 ohm, and the Max for the K2837 is 0.19 ohm, and the FQA is at 0.2 ohm.
Other than those differences as stated above, the datasheets are identical in every other value. The problem is that I am not certain the datasheet is correct for the K2837 that I found, or is really the same specs as for the 2SK2837?

Is it safe to say that the FQA is an adequate replacement? Does higher power have potential to damage other components? Are the Derating Factor, Thermal Characteristics, and the Static Drain Values On-Resistance values similar enough to be able to use?

If I go with the FQA24N50, what is the correct resistor value for that mosfet?

Thank you.
 

Attachments

  • K2837 datasheet.pdf
    508 KB · Views: 153
  • FQA24N50 datasheet.pdf
    1.5 MB · Views: 161

I'd want to see schematically, how resistors are put "across" the FETs.
It makes no sense to me, for them to be "across" S-D unless you want
a hella heater.

I am surprised you can't find 1.9 ohm 1/4W resistors, but the tolerance
may be your problem. Might try buying more (say) 1.9 ohm 0.5% or
1% resistors than you need, and hand select the closest. Might go up
in wattage. At that value you probably need a 4-wire ohmmeter /
bench metwe w/ 4-wire resistance capability. Or a pair of meters,
measure Iforce on one and Vsense across the other and do math.
But looking for 0.25% accuracy means > the usual 3-1/2 digit
cheapo DMM I expect.

For the FET, might try major mfrs' selection / cross reference tools
on the web. It's common for (at least high usage types) for there
to be "me too!" products (2SK series, maybe not so much, but try).
 

I'd want to see schematically, how resistors are put "across" the FETs.
It makes no sense to me, for them to be "across" S-D unless you want
a hella heater.

I am surprised you can't find 1.9 ohm 1/4W resistors, but the tolerance
may be your problem. Might try buying more (say) 1.9 ohm 0.5% or
1% resistors than you need, and hand select the closest. Might go up
in wattage. At that value you probably need a 4-wire ohmmeter /
bench metwe w/ 4-wire resistance capability. Or a pair of meters,
measure Iforce on one and Vsense across the other and do math.
But looking for 0.25% accuracy means > the usual 3-1/2 digit
cheapo DMM I expect.

For the FET, might try major mfrs' selection / cross reference tools
on the web. It's common for (at least high usage types) for there
to be "me too!" products (2SK series, maybe not so much, but try).
The resistors are thin wire leads and the pcb holes are small too, and will not accommodate a thicker lead as found on a higher watt rated resistor.
 

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My dead welder has mosfets labeled as TOSHIBA K2837. After an extensive 3 week search, I found data sheets with conflicting information. Until today, I could not know which ones were accurate. Now, I know why no one was able to offer help. Several sheets showed K2837 with exact specs to the Toshiba 2SK2837. Other sheets showed values that had higher values than the 2SK2837. I convinced myself that any mosfet labeled as "K2837" could not be trusted and were likely conterfeit. So, I decided to search for a mosfet with the higher Amp and higher Watt specs that were showing up. I wasted many hours. I could not find any mosfet labeled as K2837, that had higher values, and all were showing specs for the 2SK2837. Today, I decided to compare the physical part I have, to the images shown on the spec sheets I found. The actual part on my welder matches exactly to the physical shape being illustrated on the 2SK2837 spec sheets. Had I thought of looking beyond the numbers, I could have saved myself a lot of time! Turns out the datasheets are NOT for comparing specs alone. The images matter. The image shown on the K2837 sheets with higher values, does not look like my part. What a surprise it was to learn that all along that I actually have and need to find replacement 2SK2837 mosfets!

I found the FQA24N50 is nearly a perfect match to those higher values spec sheets. Those higher values consist of 271W versus 150W, 24A v 20A, and many other specs vary, see the attached data sheets below, for the K2837, the 2SK2837, and the FQA24N50 mosfets.

Before I go and buy a dozen 2SK2837 mosfets as replacements, what if any, would be considered a better/stronger/more durable mosfet to use in a multiprocess welder (model is analog "SUPER-200P")? Could a "stronger" mosfet, as the FQA24N50 mosfet be used, or would it cascade detrimental damage to other components?

Without feedback, I am looking to purchase a dozen 2SK2837 mosfets to start repairing and rebuilding my Upper Board.

Thanks.
 

Attachments

  • 2SK2837_datasheet_en_20090929.pdf
    449 KB · Views: 141
  • FQA24N50 datasheet.pdf
    1.5 MB · Views: 157
  • K2837 datasheet.pdf
    508 KB · Views: 146
Last edited:


Regarding "1.9R 0.25%" resistors, I presume you are misreading the marking. Can you explain how you arrived at the value? As others, I have no idea about their circuit function, please show a schematic sketch. 0.25% makes no sense in a power circuit anyway.
 

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