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  1. #1
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    PNP Non-Inverting Driver

    Hi,

    Bellow shown the PNP driver circuit.

    Please anyone can tell me why the input=LOW then the Emitter=UN-know logic? The design is it correct? The 7405 output is open-collector, If the 7405 input is un-know logic so what is the actual 7405 output?

    How to design the Non-Inverting Driver using PNP transistor?

    Thank You

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  2. #2
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    Re: PNP Non-Inverting Driver

    The design is correct, as far as the Emitter-follower circuit is concerned, but logic levels are not ..
    The VIL (input-low-level-voltage) for TTL family is <0.8V and this circuit produces voltages above that level (with input at or within <VOL - output-low-level-voltage) ..

    "Unknown logic" input may be misinterpeted by the 7405 gate as a 0, a 1, or simply noise ..

    One PNP transistor can't be used as non-inverting TTL buffer/driver ..

    Regards,
    IanP


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  3. #3
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    Re: PNP Non-Inverting Driver

    Hi,

    May i know, how can i improve the design?

    Thank You.



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  4. #4
    Advanced Member level 5
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    Re: PNP Non-Inverting Driver

    I am afraid you can't do much about single-transistor non-inverting-driver, however, by re-configuring it and adding second stage you can design a working TTL non-inverting-driver .. see picture below ..

    Regards,
    IanP



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