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I am practicing with some basic circuits based on bipolar and MOSFET transistors and have faced with an interesting behavior. I have to extract my PNP transistor from a circuit and have found it traces a signal between its pins as it should not be.

Bipolar transistors should give a drop in voltage between base and two others pins (~0.7V, but might vary). In case of PNP transistor (A684) a positive probe on a base (pin 3) and a negative probe on a collector (pin 2) or an emitter (pin 1) shows zero voltage (0V) on multimeter display which is set it diode tracing mode. It is a PNP transistor, so negative\ground probe should stay on base pin.

However, when I put a positive probe on a base (pin 3) and a negative probe on an emitter (pin 1), it shows drop in voltage (~0.7V). Also a positive probe on collector (pin 2) gives a drop in voltage between collector and emitter (pin 1) which should not happen at all if there is no voltage on base!

I double checked my theoretical knowledge about bipolar transistors work by this publication (note: it has not correct data in pictures, but data in tables are ok!), so it should work like this.

I have a set of 10 transistors which I recently bought in the shop. I knew the case when a whole delivery from a Chinese manufactory was broken, but because I am new in electronics I might miss an important thing here which I hope to spot and understand with your help. Thanks!

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  • \$\begingroup\$ @ Gleichmut - you have checked your "theoretical knowledge about bipolar transistors" by using the linked publication, which does not say anything about how a BJT really works? \$\endgroup\$
    – LvW
    Commented May 1 at 12:28
  • \$\begingroup\$ @LvW It is a wrong link, I just updaded with a correct one. Do you have anything to say regarding the question? Do you agree on what I should expect from PNP transistor and the data I measured tell us it is broken? \$\endgroup\$
    – Gleichmut
    Commented May 1 at 12:35
  • \$\begingroup\$ Show us the circuit diagram of a circuit that you have built. \$\endgroup\$
    – G36
    Commented May 1 at 12:54
  • \$\begingroup\$ @G36, the question is not related to a circuit. I used a circuit from a Horowitz and Hill book (2.11), but it is for NPN transistors and I can not use PNP transistors instead which I have in stock. \$\endgroup\$
    – Gleichmut
    Commented May 1 at 12:59
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    \$\begingroup\$ Take a look here pdf1.alldatasheet.com/datasheet-pdf/view/1016224/MCC/… \$\endgroup\$
    – G36
    Commented May 1 at 13:26

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From your measurement result it looks like you have misinterpreted the transistor pinout. Your base is an emitter in reality.

Here you have a clear view of a pinout:

enter image description here

The Panasonic datasheets show the same pinout but are viewed from the bottom.

enter image description here

And this is why you were confused.

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  • \$\begingroup\$ I thought Panasonic image shows transistor projection from the top view, electrodes here just a projection from the bottom view. Thank you for made it clear. \$\endgroup\$
    – Gleichmut
    Commented May 2 at 8:38

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