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SN74LVC8T245: Output stage question

Part Number: SN74LVC8T245

For the SN74LVC8T245, the the B-Port outputs allow for the following use case?

The aim is to reverse bias the diode when A-port input is high.

  • Hi Gregory,

    This is a common use case with logic. https://training.ti.com/TLM-APP-DrivingLED?cu=1134826

    Please watch this video to size your resistor properly if you have not already done so but yes this should work.

    Thanks!

    -Karan

  • When the A input is high, the B output is at 5 V, so the voltage drop over the diode is zero (not negative).

    To get a reverse bias, you would have to switch not only the cathode high, but also the anode to a lower voltage.
    Is it actually necessary to have a reverse bias?

    The forward voltage of the IR LED is so low that you do not actually need 5 V; you could drive it from 3.3 V (if you have the drive strength). Using the SN74LVC8T245 for this makes sense only if you are already using it for other purposes, and have some channels left.