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How to identify pins

Discussion in 'General Electronics Discussion' started by James W, Jul 29, 2021.

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  1. James W

    James W

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    Jul 29, 2021
    How can I identify the different pins on a transistor, like BC547 or something? What would happen if I connect them the wrong way?
     
  2. Bluejets

    Bluejets

    5,145
    1,075
    Oct 5, 2014
    Look up the spec sheet on any search engine.
    Transistors are usually viewed from the underside to get correct pinout.
    Connecting the wrong way usually ends up in disaster, and it lets the smoke out.

    Other than that, there is a very cheap test device shown as an example below.
    Can be invaluable at times, especially if the device has no numbers or numbers cannot be recognised in a search.

    https://www.ebay.com.au/itm/234077292455?hash=item36801807a7:g:hS8AAOSw~oVg4rTy

    T_tester.jpg
     
    James W likes this.
  3. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,500
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    Jan 21, 2010
    One way is to look at the datasheet for the transistor.

    Another way is to use a multimeter on the ohms range or diode check range to measure the base-emitter and base-collector forward resistance/voltage. The base-emitter junction will likely have a higher voltage drop (or resistance) than the base-collector junction.

    Too find the base, simply connect one probe of the meter to one lead one the transistor. Then use the other probe to check both other leads.
    • If both show other than open, you have found the base on your first try. The readings you got were for the base-emitter and base-collector (figure them out as above)
    • If both show open, then you also found the base with your first try, just with the wrong probe. Use the other probe on the first pin and you should see readings for both other pins.
    • If only one shows a reading, that is the base. Leave that connected to the second probe and use the first probe to get readings on the other 2 leads.
    • If something else happens, you either haven't followed the instructions, or you have something other than a bipolar transistor.
     
    James W likes this.
  4. James W

    James W

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    Jul 29, 2021
    Thank you!!
     
  5. James W

    James W

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    Jul 29, 2021
    Thanks! You've been really helpful
     
  6. Martaine2005

    Martaine2005

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    May 12, 2015
    upload_2021-7-29_10-47-34.jpeg
    Martin
     
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