[SOLVED] 555 Timer IC monostable

[alexan_e]

https://en.wikipedia.org/wiki/Duty_cycle

The duty cycle is defined as the ratio between the pulse duration and the period of a rectangular waveform

In a monostable you only have the duration of the pulse but not the period so no duty cycle can be calculated.

If for any reason the monostable is part of a bigger circuit and is triggered by an event at stable intervals then you can calculate a period and based on that a duty cycle.

Alex

 

[Syncopator]

In monostable, how long we trigger is the trigger time. If I trigger it for 10 minutes then during this time I get output high.

"Trigger time" is not an expression that we use. We can talk about the trigger pulse's width or duration, or its repetition rate.

Generally, the trigger pulse to a monostable should be very short. In some designs of mono, such as one using the 555, the output will remain high if the trigger remains low.

Others, such as the two-transistor cross-fed monostable, would not repsond until they receive another transition, of the correct polarity, at its trigger input.

"Trigger for 10 minutes" would indicate, unless you state otherwise, that the monostable is receiving a series of pulses over a period of 10 minutes, not a single pulse of 10 minutes duration.


The duty cycle of an astable is designed into it. We design it to have a know repetition rate (frequency) and a known duty cycle. We apply power and it gives us pulses at a known frequency and of a known duty cycle.

We can't design that into a monostable. Switch it on and it does nothing. Apply a trigger pulse and it produces a single pulse of known duration. That's all.

Nor can we design a duty cycle into a bistable. Switch it on and it does nothing.
Apply a pulse to its set input and it changes state. That'all. It doesn't produce a pulse. It then sits there doing nothing ... unless or until you apply another pulse, to its reset input, whereupon it revertsto its original state.

 

[pebe]

Quote. "If I trigger it for 10 minutes then during this time I get output high. right?".

No. You don't trigger it for 10 minutes. The trigger pulse is only a very short pulse that 'kicks' the monostable into action. The trigger pulse must have ended before the end of the On period.

Edit:
Sorry Syncopator, I somehow seem to have missed a couple of posts, because I was answering from an email notification and it took me back to the wrong posting.

 

[Eshal]

Hi experts. How are you?

Now I realize. I am confusing with words duration and period as said in this definition,

The duty cycle is defined as the ratio between the pulse duration and the period of a rectangular waveform

 

[pebe]

They both mean the same thing, so they are interchangeable.

Dictionary definition of 'duration' or 'period':- "noun 1. the length of time something continues or exists"

 

[Eshal]

OK
:-?
Thank you.

 

[alexan_e]

Pebe, I think you are confusing Eshal.
What the definition says is The duty cycle is defined as the ratio between the pulse duration and the period of a rectangular waveform

By pulse duration is means the duration for which the output is active (high)

 

[pebe]

alexan_e, I hope I didn't confuse Eshal.

The point that I was trying to make was that both terms relate to time, because in this context 'duration' is the time from beginning to the end of the pulse, and 'period' is the time between one pulse and the next.

 

[Eshal]

Now I am clear about duration and period. Thanks both.
But give me some time. I will post final understanding what I understand about this topic.

 

[Eshal]

I read overall discussion and finally, I think, I have gotten answer. I was confused about duty cycle.
Now it is cleared to me why monostable doesn't have cycle.

But now tell me why bistable has duty cycle? why why why????

 

[pebe]

Eshal,
A bistable does NOT have a duty cycle, unless you define how long it is in each state.

 

[Syncopator]

But now tell me why bistable has duty cycle? why why why????

I thought that I had explained that in my post #22.

 

[Eshal]

Yes thank you both. All people helped me. thank you very much.