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RTL logic 0 and 5 V

Discussion in 'General Electronics Discussion' started by Virium, Jul 3, 2016.

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  1. Virium

    Virium

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    Jun 27, 2016
    Hello everybody, just a small question about logic.
    What would be the best way for me to force an output of 5 volts out of a more complex circuit using multiple transistors and resistors. For example in the picture the output is about 3.3 V. Should I play around with resistors, use a comparator or something else ?
    And on the opposite side, if I were to feed back the output into one of the inputs, what would be the best way to force the new output to be 0 volts ?
    Thank you for reading
     

    Attached Files:

  2. Harald Kapp

    Harald Kapp Moderator Moderator

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    Nov 17, 2011
    SInce the emitter voltage of the output transistor(s) is at least ~0.6 V less than the base voltage and the base voltage can't be higher than Vcc (5 V), the output will alway be at least Vcc-0.6 V or less. Much less in your circuit since the output of the intermediate stage(s) is already at less than Vcc.
    Use PNP transistors in the output to get (almost) full Vcc at the output (Vcc-Vcesat, to be precise).


    Since the output is passively pulled down to 0 V by a 10 kΩ resistor, the low output voltage depends on the load resistance to Vcc.Your circuit's inputs have a very high impedance to Vcc. Current will flow only when the input voltage is > 0.6 V. When you connect such an input to the output of your circuit, you will therefore see a good 0 V low signal.
     
  3. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    Harald, if he uses a single PNP won't his logic will be inverted?

    Chris
     
  4. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    This circuit will keep your logic intact. If you want to make the output TTL compatible reduce R21 to about 1KΩ to 2KΩ.

    Chris
    upload_2016-7-3_10-45-0.png
     
  5. Harald Kapp

    Harald Kapp Moderator Moderator

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    Nov 17, 2011
    Of course this would have to be taken into account.
     
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