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TLC555-Q1: Timer used as an astable multivibrator

Prodigy 10 points

Replies: 2

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Part Number: TLC555-Q1

If we use this TLC555-Q1 Timer IC as an Astable multivibrator,it is possible to generate 40% duty cyle ,1KHz square Wave ?

as per LTspice simulation the duty cycle is less than 50% is not set. so it is any limitation for duty cycle ?

  • Hello Avadhut,

    For 50% and lower, it is common to add diode to bypass Rb as seen in the TCL555 calculator http://www.ti.com/lit/zip/slvc100

    There is another way to get a little lower than 50% Duty cycle. This gives 1kHz 40% without a diode . Rd is set to 47% of Ra

    Here is the expected relationship between Rd/Ra and output duty cycle. Notice the "cliff" near 30% DC (50% Rd/Ra)"

    TLC555 1kHz 40%.TSC

     

    Regards,
    Ronald Michallick
    Linear Applications

    TI assumes no liability for applications assistance or customer product design. Customer is fully responsible for all design decisions and engineering with regard to its products, including decisions relating to application of TI products. By providing technical information, TI does not intend to offer or provide engineering services or advice concerning Customer's design. If Customer desires engineering services, the Customer should rely on its retained employees and consultants and/or procure engineering services from a licensed professional engineer (LPE).

     

  • In reply to Ron Michallick:

    Avadhut,

    Here is an alternative option. The value of Rd becomes less critical with the addition of the Rb resistor.

    The original circuit operates at the red square and the new circuit at the blue square. (the axis' are swapped in this new chart)

    For 40% duty cycle, the blue will be just a little bit more accurate as the slope of the line is greater and father from the "end of range" 

    Either would work well at 1Khz.

    Regards,
    Ronald Michallick
    Linear Applications

    TI assumes no liability for applications assistance or customer product design. Customer is fully responsible for all design decisions and engineering with regard to its products, including decisions relating to application of TI products. By providing technical information, TI does not intend to offer or provide engineering services or advice concerning Customer's design. If Customer desires engineering services, the Customer should rely on its retained employees and consultants and/or procure engineering services from a licensed professional engineer (LPE).

     

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