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I have this demultiplexer and I need to configure it in such a way that I can control 8 transistors using its outputs. They NEED to be NPN transistors, so when I select an output using the addresses, it must give me logic level 1, not 0. The problem is, in the data sheet of this multiplexer there is a logic table and according to it there doesn't seem to be any possibility of getting a HIGH logic level at the selected output, and only LOW logic levels at the other, not selected, outputs. Is there a way I can do that using this demux?

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3 Answers 3

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Just add a second NPN as an inverter.

schematic

simulate this circuit – Schematic created using CircuitLab

Adjust resistor values and add speed-up caps and/or Schottky clamps to meet your speed and current requirements.

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  • \$\begingroup\$ Or a set of 8 inverters or "inverting drivers": eg instructables.com/id/… \$\endgroup\$
    – pjc50
    Dec 11, 2014 at 15:31
  • \$\begingroup\$ That is probably the better solution, since the NPN requirement was there, I went with the assumption there were a lot available. \$\endgroup\$
    – Matt Young
    Dec 11, 2014 at 15:32
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Absolutely. Use a 74HC238 instead, which does what you're looking for.

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  • \$\begingroup\$ Yeah, but I was thinking if I could somehow do it with this one, because my electronics shop doesn't have any other one in stock. \$\endgroup\$
    – Calin
    Dec 11, 2014 at 14:38
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You could use a 74HC238 instead. Its got active-high outputs instead of the '138's active-lows.

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