I am working on following circuit involving BC107 NPN Philips TO-92 transistor and voltage source of 4.2 V.


simulate this circuit – Schematic created using CircuitLab

I got some confusion when measuring collector's current. I was expecting that to be at least 0.2 A but when I insert probes and measure current as shown in the picture I get a reading of 0.0079 A. That would mean an DC Gain (beta/hFE) of Ic/Ib=0.0079/0.0023=~3.37, while this transistor should yield a gain of about 40-200 (I do not have spec for TO-92 though, it's taken from datasheet for BC107 TO-18, can't find any spec for TO-92...).

I would like to understand why am I getting 0.0079 reading when the base current (Ib) is 0.00234 A (confirmed with multimeter).

Ib = (4.2 - 0.7) / 1480 = 0.0023

Ic (expected) = Ib * hFE = 0.0023 * [40:200] = [0.092:0.460] [A]

but real Ic = 0.0079 [A]

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  • \$\begingroup\$ Comments are not for extended discussion; this conversation has been moved to chat. Any conclusions reached should be edited back into the question and/or any answer(s). \$\endgroup\$
    – Dave Tweed
    Dec 23, 2018 at 17:29

1 Answer 1


You appear to have the transistor connected backwards. Collector is grounded and emitter is used as a collector.

The transistor will work that way, but will have a really low beta, often in the range you are seeing. The Vceo breakdown will also be very low, but okay for your 5V supply. Image from this site.

enter image description here

  • \$\begingroup\$ Yes, we've already fond I used wrong datasheet. Actually I can't find a datasheet for this supposedly "BC107/PH10440 PHILIPS (TO-92) PLASTIC NPN" and I think I will just put it on the shelf and get back to learning transistors using one I am more sure about. \$\endgroup\$
    – 4pie0
    Dec 23, 2018 at 16:51
  • \$\begingroup\$ The Chinese often will take part numbers that point to a particular package and cavalierly re-use the part number for a different (more popular) package. I have reels of so-called 1N4004, 1N5819 diodes in surface mount packages, for example. When western companies re-used the part number for the hermetic 2N2222 for example, it was usually called something like PN2222 in TO-92, and the TO-92 2N3904, for example, became MMBT3904 in SOT-23. But that example has not been followed. \$\endgroup\$ Dec 23, 2018 at 16:57
  • \$\begingroup\$ But the USA BJT's ( PN2222A ) will have a different pinout. \$\endgroup\$
    – G36
    Dec 23, 2018 at 17:46
  • 1
    \$\begingroup\$ @G36. Yes, there are three common TO-92 pinouts. American (EBC) eg. 2N3904, European (CBE) eg. BC547 and Japanese (ECB) eg. 2SC1815. You can find parts like 8050 in more than one TO-92 pinout, just to keep you on your toes. Fortunately almost all SOT-23 BJT pinouts are the same. \$\endgroup\$ Dec 23, 2018 at 17:55

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