I was testing few types of transistors on my newly acquired peak atlas pro and came across some N-channel depletion mode JFETs marked 2n3819. To my surprise the device indicated they are NPN BJTs. Using my fluke multimeter in diode mode, the voltage drop from centre pin (2) to other two (1,3) was a normal diode voltage drop for each pair and also resistance between 1 and 3 was OL. I understand that if they were real JFETs, the resistance between drain and source would be low, which is not the case for these transistor as they showed OL. Additionally, Peak atlas showed the parameter as hFE=286 at Ic=5mA, Vbe= 0.749v at IB=5Am etc. I am confused, according to the peak atlas manual, the analyser should be able to identify and analyse JFETS. Are my transistors faulty or fake ?

  • \$\begingroup\$ Your tests convince me...BJT. If you short "gate" to "source", can you get current through the channel (drain-to-source)? If so, do some more testing. If no current flows, they're BJTs. \$\endgroup\$
    – glen_geek
    Mar 31 '17 at 14:14
  • \$\begingroup\$ @glen_geek I shorted gate to source, then test the drain to source by placing red probe of multimeter on drain and black on shorted source. It showed OL for both voltage drop and resistance. It also showed 0.618v when I reversed the probes. Does that mean they are BJTs? \$\endgroup\$
    – Rio.H
    Mar 31 '17 at 16:10
  • \$\begingroup\$ OK test with one caveat: some DVM ohmmeters fail to detect diodes properly (your tests suggest that your meter does OK). I just tested a REAL FET (J309) like you did...it showed 45 ohms on a couple different ohmmeters. I'd guess a real 2N3819 might come out somewhat higher...maybe 200 ohms. Your same test showed OL. Am leaning more towards...BJT (not FET). \$\endgroup\$
    – glen_geek
    Mar 31 '17 at 17:42
  • 2
    \$\begingroup\$ Ok, lesson learned, never buy transistors from ebay. \$\endgroup\$
    – Rio.H
    Mar 31 '17 at 19:49

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