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LM393: LM393

Part Number: LM393
Other Parts Discussed in Thread: LM321LV, LM358


  I would like to know  i came across a old design that  LM393D part is used for LED  brightness control without pull up resistor on output.Is it possible LM393D will work without pullup resistor on output?



  • The LM393 has an open-collector output. When the output is off, no current flows, and the voltage floats. If you wanted to get a defined high voltage, you would need a pull-up resistor, but if all you care about is the current (through the LED), then you do not need it.

  • Hello Saravanan,

    You do not need a separate pull-up resistor if the load goes to a positive voltage.

    The LED and it's associated series current limiting resistor to the positive supply is all that is needed. You do not need a parallel pull-up.

  • Hi ,

       I add some clarity i have a MCU GPIO which can generate PWM  other end  we are going to control 20x4  character LCD  Vo pin(Part No :  WH2004G).Herewith i have attaching the circuit for your reference.



  • The WH2004G wants the VO control voltage to be at nominally VDD − 4.2 V. Apparently, sinking current is enough to achieve that, but only because of how the WH2004G circuit happens to be implemented.

    Anyway, the LM393 is just uses as an analog buffer. I guess it was not really chosen, but a comparator was still available in the dual package. Any random opamp (½ LM358 or LM321LV) would work just as well.