Operating NE555 as astable vibrator

[electronic engineer]

When Operating NE555 as astable vibrator

In how many ways can we make the ON pulse exactly equal to OFF pulse?

 

[berkeman]

Can you post a link to a datasheet for the 555? What specs for duty cycle are listed? BTW, is this a homework problem?

 

[Averagesupernova]

If I recall correctly, it is NOT possible to obtain a perfect 50% duty cycle output with a 555.

 

[electronic engineer]

let's look into the internal structure of 555, we see pin 5 (voltage control pin) plays its role as voltage alternator for threshold voltage of upper comparator so charging time of external capacitor C changes thus the frequency of osscillation changes , but i don't know how to get exactly 50% duty cycle (Mark=Space), how to get charging time equal to discharging time??
does the threshold changing of upper comparator result in corresponding threshold change of lower comparator?!

i need help , thanks

 

[electronic engineer]

let's look into the internal structure of 555, we see pin 5 (voltage control pin) plays its role as voltage alternator for threshold voltage of above comparator so charging time of external capacitor C changes thus the frequency of osscillation changes , but i don't know how to get exactly 50% duty cycle (Mark=Space), how to get charging time equal to discharging time??

what's the relation between control voltage and discharging time?

 

[berkeman]

but i don't know how to get exactly 50% duty cycle (Mark=Space)

If the 50% duty cycle is important to you, just run the 555 at 2x frequency, and add a divide-by-2 flipflop after the 555. Or use a better oscillator than the 555.