Question in 555 timer circuit

[mick1027]

Hi,

I assume this might be a fundamental concept so hopefully I will understand with a brief explanation. I would like some more understanding of how the comparator works on pin 6 in the below schematic.

The comparator on pin 6 will 'read' the voltage on the C1. I understand when C1 gets to a high enough level ( greater than 2/3 of source voltage ), then it will result in a different state being sent to the flip flop. My question is regarding the comparator that sits on pin 6. How does the same voltage that is charging the capacitor ( C1 ) not interfere ( for lack of better words)? Please let me know if I need to clarify or ask in a different way. thanks!

 

[Bluejets]

http://www.williamson-labs.com/pu-aa-555-timer_very-slow.htm

 

[dorke]

Your understanding is correct.
The inputs of the 2 comparators inside the 555 have very high resistance,
i.e no current flows into pins 2 and 6 (blue arrows).

The capacitor charging current is the red arrow.

 

[mick1027]

Your understanding is correct.
The inputs of the 2 comparators inside the 555 have very high resistance,
i.e no current flows into pins 2 and 6 (blue arrows).

The capacitor charging current is the red arrow.

View attachment 23463

Understand now.. I was also stuck on understanding the voltage and the fact it is the equal ( both compararators and capacitor in parallel) after the resistor ( resistor that is in series right before pin 6 ). The voltage is 0 ( since the capacitor is charging ) . Voltage will increase as the capacitor reaches the max voltage ( equal to voltage drop is across the resistor before pin 6).

Your picture / validation helped. thanks!