Timer IC-555 is the one of the most commonly used general-purpose linear integrated circuits.
The Timer IC 555 comprises two Op-Amp comparators, a flip-flop, a discharge transistor, a reset transistor, three identical resistors and an output stage. The resistors set the reference voltage levels at the non-inverting input of the lower comparator and inverting input of the upper comparator at +VCC/3 and 2VCC/3, respectively. The output of two comparator feed SET and RESET inputs of the Flip Flop. This decided the logic state of its output and subsequently the final output. The Flip-Flops complementary outputs feed the output stage and the base of the discharge transistor. Hence, when the output is HIGH, the discharge transistor is OFF and when the output is LOW, the discharge transistor is ON.
