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Duty Cycle

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Is there any effect of changing the duty cycle of a 555 timer to be greater than 50% to drive a counter? (74163 4 bit binary counter)


using a 555 timer with a 1Hz frequency and a 50% duty cycle to drive counter.

Change this to

75% duty cycle @ 1Hz.

Would there be any difference in the count sequence.? My opinion is that there should be no change as it is the frequency that determines the count speed. If this is the case why bother using 50% duty?




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look at the datasheet for the 163 (tell me you aren't using the original TTL...). count happens on rising edge. so duty cycle *mostly* doesn't count.

50% duty cycle is so that you can get the highest possible clock rate. minimum clock low and high (from datasheet) are the same, thus any clock duty cycle other than 50% will reduce the max frequency. In practice, it really doesn't matter. If you are running that close to the spec, you probably should move to a higher frequency chip.
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