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POSSIBLY FAKE TRANSISTORS

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m3vuv:
Hi all,a few months ago i brought some tip 122 transistors from ebay, (uk seller),just stuck them im my chineese component tester and the max hfe is 45,it marks them as a bipolar not darlington,could these be fake or is there a non darlinton version of the tip 122 that i dont know about? TIA

Kleinstein:
The TIP122 has base to emitter resistors and a relatively small one for the larger transistor.  With low current this reduces the gain quite a bit and the transistor may look like a non darlington.  It may need more current (e.g. 100 mA) to test this transistor.

m3vuv:
does that mean a 328 based tester cant measure this?,or see if its a darlington or not then,if so i guess that would explain it??,TIA.

Kleinstein:
The µC based transistor tester likely can't do a proper test and would see it as a simple transistor with reduced gain. So showing a gain of 45 may well be OK. So chances are the transistor is OK.

Chances are the diode test between base and emitter would also show a lower reading than normal for a darlington, as the transistor includes 2 extra resistors. One may measure the resistance base to emitter, that should be some 8 K +-50%

Kim Christensen:
Ditto to what Kleinstein said. The 328 based testers can only supply low current (a few mA) and low voltages (less than 5V) to the transistor under test. So they don't really work that well when testing higher current/voltage/power devices. For that you would use a curve tracer. But for the hobbyist on a budget, a power supply, DMM, and some resistors makes an adequate DIY test for power transistor beta.
ie: Put a few milliamps into the base and observe how much collector current flows. Do the simple math and you have your beta.

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