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LM393B: an you help me find the values for R8, R18, R9, and RL?

?? ?
Prodigy 60 points
Part Number: LM393B

Tool/software:

an you help me find the values for R8, R18, R9, and RL?

I want to set the initial voltage at the CDS_3V node, which is connected to the non-inverting input (+) of the comparator, to 0.48V.

The output of the comparator (CDS_OUT) should be between 10V and 12V when it is active.

When the comparator is triggered, I want to use a feedback resistor (RL) connected from CDS_OUT back to the non-inverting input (+) to increase the voltage at CDS_3V to above 2V.

Is there a way to achieve this behavior?

  • 0
    Guru 316780 points

    When you say "CDS_3V", do you mean CDS_3V, or the point between R8 and R13? In the latter case, give it a name and use that name.

    What is the voltage at CDS_3V?

    What do you mean with "active"? What do you mean with "triggered"?

  • 0 in reply to Clemens Ladisch
    TI__Genius 11045 points

    Clemens is asking the right clarification questions. From the schematic itself, it seems like you're trying to create an inverting comparator with hysteresis.

    Also, this is a duplicate post. Please see: LM393:an you help me find the values for R8, R18, R9, and RL? - Amplifiers forum - Amplifiers - TI E2E support forums

  • 0 in reply to Clemens Ladisch
    Prodigy 60 points 
    he voltage output from cds_3v is 3v, and I want to distribute it to R8 and R13 below to input 0.4v to the (+) pin. Additionally, I want to connect a feedback resistor to cds_out, which is pulled up to 12v, and connect that feedback resistor back to the (+) terminal.
    The CDS_OUT output value is 6V or more, and I would like the voltage that is connected to the feedback resistor and inputted back to the (+) pin to be 3V. I am curious about the values ​​of R8, R13, R9, and RL used at that time, and I am curious about the formula for calculating the values.
  • 0 in reply to ?? ?
    TI__Genius 11045 points

    Hi,

    Please respond to the post in my previous reply. Since this is a duplicate post, I'll be closing this one. Please let me know what you think of my reply on the other post.

  • 0
    Prodigy 60 points

    voltage output from cds_3v is 3v, and I want to distribute it to R8 and R13 below to input 0.4v to the (+) pin. Additionally, I want to connect a feedback resistor to cds_out, which is pulled up to 12v, and connect that feedback resistor back to the (+) terminal.The CDS_OUT output value is 6V or more, and I would like the voltage that is connected to the feedback resistor and inputted back to the (+) pin to be 3V. I am curious about the values ​​of R8, R13, R9, and RL used at that time, and I am curious about the formula for calculating the values.

  • 0 in reply to ?? ?
    TI__Genius 11045 points

    Hi,

    Since you replied to this post, I'll go ahead and continue the discussion on this post.

    Please read the circuit cookbook I shared on your other post. I'll go ahead and repost it here: Inverting Comparator With Hysteresis Circuit

    If I'm understanding correctly, you are describing an inverting comparator with hysteresis. Hysteresis means that the switching threshold (IN+ voltage in this case) changes depending on output state. This results in two distinct switching thresholds VL and VH; customers usually implement hysteresis to make the comparator insensitive to noise on the signal and prevent chattering at the output of the comparator.

    The circuit cookbook I posted above have the formulas for calculating the resistor values. You need to start by defining VL and VH for your application.

    I've also shared a hysteresis tool that helps you calculate the resistor values based on your design parameters. It will calculate values for your hysteresis resistors based on the design parameters you enter.