how to derive the formula for 555 timer which is built by using one SR-FF 2 opertional amplifer and 1 bjt 4 resistor (3 5k and one unknown) with vcc =5v

 

555 timer information that may be helpful. Or not.

hgmjr

 

I don't think a 555 equivalent can be made with only one op-amp. A comparator is needed for both threshold and trigger inputs.

 

Didn't I read somewhere that you can make a comparator out of an op amp with a simple mod...or am I just smoking something?

 

Didn't I read somewhere that you can make a comparator out of an op amp with a simple mod...or am I just smoking something?

Its not good practice, but you can use op-amps as comparators. No mod is required, but you need to check specification against application - primary areas being voltage ranges for inputs, and differential input voltage.. Also, stability can be a problem with open-loop operation of an opamp.

 

Its not good practice, but you can use op-amps as comparators. No mod is required, but you need to check specification against application - primary areas being voltage ranges for inputs, and differential input voltage.. Also, stability can be a problem with open-loop operation of an opamp.

Stability (if you're talking about possible oscillation) isn't a problem. Slew rate is a problem.