Tristated output to two common Base transistor issue


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    Join Date
    Aug 2006
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    Default Tristated output to two common Base transistor issue

    Hello,

    I have to power automotive LEDs that drain 50mA.

    I use twenty LEDS and have a 16F630, so my circuit connects two LEDs to 1 I/O port and I use the Z state to switch them OFF.

    To make this without destroying the PIC, I use transistors like this (one port example):
    <img src="http://www.picbasic.co.uk/forum/attachment.php?attachmentid=1965&stc=1&d=118901631 5">

    Problem: when I have set the port direction to Input (=Z state), both LEDs still light; less than normal, but still enough to make this look not good.

    The SMD transistors have built-in 22k resistors like this (the PNP one has same connections):
    <img src="http://www.picbasic.co.uk/forum/attachment.php?attachmentid=1964&stc=1&d=118901608 9">

    I tried to add 1k resistors at each Tr's Base, but... still the same.

    Is there a way to sort out this issue?

    NB: how do I put text beside the images???
    Attached Images Attached Images   
    Roger

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