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Old 6th May 2004, 12:31 PM   #1
Wagener is offline Wagener  South Africa
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Default how to identify fake transistors

I received a few quotes on the MJ15003 and MJ15004. One company (which supplies most of the components for our technikon) quoted about a third of the price of that of most companies.

I am concerned about buying fake transistors because the technikon aparently bought some fake products from them some time ago.

How do I chech a component to see if its fake (other that using a multimeter)
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Old 6th May 2004, 12:49 PM   #2
karma is offline karma  Canada
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there are a few threads on it do a search on fake chips

counterfiet sa1943's ??

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Old 6th May 2004, 01:11 PM   #3
sam9 is offline sam9  United States
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As a victim of fake transistors here are a couple of things to watch for:

If the price is "too good to be true" that's because it is.

If you have the means to easily measure Hfe, an unreasonably high figure (like 100++ ) from a power transistor is a sign something is not right. Mine had a tiny chip that was probably intended for a low voltage, small signal transistor.

If you have a known good copy of the transistor, beware of version where the printed label looks different. Sometimes the fakes actually have better quality printing on them than the original.
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Old 6th May 2004, 01:45 PM   #4
Eva is offline Eva  Spain
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It would be a good idea to request a sample of each and measure Hfe and B-E, B-C zero-bias capacitances

Hfe should not be too far from the figures quoted on the datasheet, but if the dies are fakes taken from other smaller power transistors then their Hfe value will be in the correct range and won't be useful for fake detection

Zero-bias junction capacitance values are very useful in determining die sizes. Each model of transistor shows typical capacitance values. Fake transistors tend to have 1/2 to 1/10 of expected capacitances due to smaller die sizes. Capacitance is roughly proportional to die area

You may post measured capacitance values on the forum, asking for other people to compare them to the ones measured on devices known to be genuine. Fakes will allways show smaller capacitances
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Old 6th May 2004, 01:46 PM   #5
jaycee is offline jaycee  United Kingdom
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Mr Elliot has a pretty good article on this:
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