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LM555: LM 555 in monostable assembly

Emanuel Calin
Prodigy 10 points
Part Number: LM555

Tool/software:

Greetings,

If on a good old 555, in a monostable assembly, the negative trigger pulse, received at around 500 Hz, is longer than the monostable output, as decided by R-C values, what shall happen ?  Shall there be a continuous output delivered, or, regardless of the length of the trigger, the output shall have the length decided by the R and C values only ?   In other words, regardless of the length of the trigger pulse, the monostable output shall have a calculated fixed length, as per R and C values.

Many thanks and best regards !

  • 0
    TI__Guru**** 164856 points

    Hello Emanuel, welcome to the TI e2e forums.

    The inputs have this priority order (greatest to least); RESET, TRIGGER, THRES

    If timing threshold is reached before trigger goes high, trigger has priority so output pulse stays high until trigger goes high (pulse extended).

    Emanuel Calin said:
    In other words, regardless of the length of the trigger pulse, the monostable output shall have a calculated fixed length,

    No, but AC coupling the trigger input can solve this issue.