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  1. #1
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    Please help me to understand the transistor circuit

    Attached a transistor circuit here. I do not understand why the base and emitter of the NPN is connected together, and what is it use for?

    Click image for larger version. 

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ID:	148255

    Thank you.

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  2. #2
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    Re: Please help me to understand the transistor circuit

    Q1 indeed looks useless for me.
    Sure this is a PNP? Where did you get this circuit?



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  3. #3
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    Re: Please help me to understand the transistor circuit

    Quote Originally Posted by eepty View Post
    Attached a transistor circuit here.
    What purpose is this circuit for ?
    For clampling Vin ?



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  4. #4
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    Re: Please help me to understand the transistor circuit

    Q1 acts as a diode with the collector being the cathode.

    Otherwise the circuit operation makes little sense to me.
    Zapper
    Curmudgeon Elektroniker



  5. #5
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    Re: Please help me to understand the transistor circuit

    I have done this (transistor as diode, B=E) many times in IC
    designs where I just wanted a plain old dumb 40V diode but
    had a CAD group who just could not be bothered to add one
    to the "blessed" library, and a modeling group who likewise
    gave zero fvcks about making a decent model. So you get
    to use what's on your plate. We would call this a "C-B
    transdiode" (transistor (mis)applied as diode).

    But the larger picture is still a mystery, it looks like the
    PNP is used upside down as well and there's nothing to
    indicate actual (let alone desired) function. Offhand it
    looks like a waste of three components.



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