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Old 23rd September 2012, 01:18 PM   #1
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Default DN2540 plate load.

I bought some DN2540 mosfet's on Ebay but i haven't seen this print before, are these fake?
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Old 23rd September 2012, 01:25 PM   #2
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Difficult to say from the outside. And looking at the inside may answer the question, but renders the answer useless.

Maybe a simple test setup which is able to drive them closely to the borders of the SOA, if the don't fail quite soon, they're probably not fake. Don't forget to mount them on a heatsink for stress tests.

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Old 23rd September 2012, 01:41 PM   #3
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It's suspect.

You have the ON (onsemi) branding, but ON don't have a DN2540 or anything-2540.

Quick test: a depletion FET should have continuity from D to S when metered with DMM on 200 ohm range, even with G floating. One of my 2540s measures 8 ohm like this.
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Old 23rd September 2012, 01:41 PM   #4
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Usually these are used as a CCS. So just build one and see how it works.
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Old 23rd September 2012, 02:05 PM   #5
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Hello Rod,

I measur around 9,5 Mohm

Quote:
Originally Posted by Rod Coleman View Post
It's suspect.

You have the ON (onsemi) branding, but ON don't have a DN2540 or anything-2540.

Quick test: a depletion FET should have continuity from D to S when metered with DMM on 200 ohm range, even with G floating. One of my 2540s measures 8 ohm like this.
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Old 23rd September 2012, 02:11 PM   #6
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Before using them as a plate load (as intended), I would test them intensely in a simple circuit, without the risk of damaging expensive amplifier parts.

Greetings,
Andreas
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Old 23rd September 2012, 02:49 PM   #7
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Here's what I don't understand- known real parts are cheap and readily available from reputable distributors on an overnight, in stock basis. Why use EBay and dodgy sellers? It's not like these are exotic, discontinued, or expensive parts.
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Old 23rd September 2012, 03:19 PM   #8
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Many European hobbyists solely use their bank account for payments while American suppliers just accept credit cards. As it seems the situation for Europeans is changing because it's possible to make a payment to Mouser via a bank in Germany, I found out a couple of months ago. Until then I had the same problem with US parts which are hardly stocked by local wholesalers (which don't sell to private persons). There's your problem
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Old 23rd September 2012, 03:48 PM   #9
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Quote:
Originally Posted by brommermartin View Post
Hello Rod,

I measur around 9,5 Mohm
Sad to say, that sounds like a relabelled bipolar transistor, or enhancement-FET.

You can try it in a CCS connexion - but my guess is that it will give a current of zero, if it is the fake we suspect it to be.



Yes, in Europe, Mouser is the only practical access to any kind of franchised supply of any depletion-FET, but this works only for GBP 50 orders (in the UK) - or you pay high shipping costs.
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Old 23rd September 2012, 03:52 PM   #10
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... O, if you test it in a CCS circuit, please try the test at 30V (or 20 - 45V) first.
If it is a fake, the VDS or Vce breakdown might only be 50V.
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