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How to improve upon this comparator driven LED circuit?

Discussion in 'LEDs and Optoelectronics' started by Angy15, Feb 9, 2016.

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  1. Angy15

    Angy15

    27
    0
    Nov 18, 2015
    If Vcc is less than 23V transistor is ON LEd2 & buzzer operates and if VCC is greater than 23V it is OFF buzzer does not operate and LEd1 is ON. But somewhere between around 23.100V both LED 1 and Led2 are ON and there is some sound in buzzer. This effect is happening when there is transistion from VCC>23V to VCC<23V somewhere around 23.1V. How can I improve upon on this circuit so that there is immediate switching between Voltage levels .

    This circuit is a part of complete schematic in which when Voltage at Pin2 is greater than Pin 3 output Pin 1 is low and when voltage at pin 2 is less than pin 3 output Pin1 is high .
     

    Attached Files:

  2. Alec_t

    Alec_t

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    804
    Jul 7, 2015
    What is the buzzer voltage rating?
    Do you want LED1 to be on when LED2 is off, and vice versa?
     
  3. Amar Dhore

    Amar Dhore

    129
    12
    Dec 2, 2015
    what are your input voltages? what is your common mode voltage?
     
  4. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    Google "hysteresis".
     
  5. AnalogKid

    AnalogKid

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    718
    Jun 10, 2015
    You don't give the opamp input conditions for the various Vcc conditions, so there is no clear answer.
    Also, what is the purpose of R1?
    Also, what is the need for Q? If the LM158 can sink enough current to light LED1, can't it source enough current to light LED2?

    ak
     
  6. Angy15

    Angy15

    27
    0
    Nov 18, 2015
    Buzzer voltage is 25V.
    Yes I want LED1 to be ON when LED2 is OFF and vice versa
     
  7. Angy15

    Angy15

    27
    0
    Nov 18, 2015
    actually I am using LM339 thats why I am using R1
     
  8. AnalogKid

    AnalogKid

    2,520
    718
    Jun 10, 2015
    In that case you will have only about 1 mA through LED2.

    Again, there is nothing in your schematic that would cause the device output to change state because of a variation in Vcc. No input circuit, no good answer.

    ak
     
  9. Colin Mitchell

    Colin Mitchell

    1,416
    313
    Aug 31, 2014
    What you need to do is add a Schmitt Trigger. Either turn the op-amp into a Schmitt Trigger or replace it with a Schmitt Trigger.
     
  10. Alec_t

    Alec_t

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    Jul 7, 2015
    Something like this, perhaps?
    LEDBuzzerSwitch.PNG
     
  11. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,497
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    Jan 21, 2010
    you need a resistor acrod the greed led and its resistor to prevent the LED from turning on a little when the output is supposed to be high.

    The original circuit was correct in this respect.
     
  12. Amar Dhore

    Amar Dhore

    129
    12
    Dec 2, 2015
    1. Why is your VCC is changing?
    2. What are your inputs?
    3. What is purpose of R1?
     
  13. Alec_t

    Alec_t

    2,978
    804
    Jul 7, 2015
    Oops, forgot that. A 1k resistor directly across the green LED in the post #10 circuit should do the job.
     
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