#### Astable Multivibrator using 555 Timer IC

jojo June 20, 2017 27 Comments
In this article, we are explaining an astable multivibrator, often called a free-running multivibrator.Â An astable multivibrator can be designed using different types of components, say using transistors (and associated components) alone or by using op amps (and associated components). In this article, we are designing an Astable Multivibrator using 555 Timer IC. If you are wondering what all are the practical applications of an astable multivibrator, lets begin by seeing a few. One of the most common application for...

#### 555 Timer IC Working Principle

jojo February 25, 2014 11 Comments
Block Diagram of 555 timer IC:       Comparator 1 has a threshold input (pin 6) and a control input (pin 5). In most applications, the control input is not used, so that the control voltage equals +2/3 VCC. Output of this comparator is applied to set (S) input of the flip-flop. Whenever the threshold voltage exceeds the control voltage, comparator 1 will set the flip-flop and its output is high. A high output from the flip-flop...

#### 555 Timer IC Block Diagram

jojo April 7, 2011 No Comments
Block diagram for the 555 timer is given in figure. As shown in the block diagram, a 555 timer consists of two comparators (simply op-amps), an R-S flip-flop, two transistors and a resistive network Resistive network consists of three equal resistors and acts as a voltage divider. Comparator 1 compares threshold voltage with a reference voltage + 2/3 VCC volts. Comparator 2 compares the trigger voltage with a reference voltage + 1/3 VCC volts. Output of both the...

#### 555 Timer IC Basics

jojo April 7, 2011 No Comments
The 555 timer combines a relaxation oscillator, two comparators, an R-S flip-flop, and a discharge capacitor.   R-S Flip-Flop. A pair of cross-coupled transistors is shown in figure. Each collector drives the opposite base through resistance RB. In such circuit one transistor is saturated while the other is cut-off. For instance, if transistor Q1 is saturated, its collector voltage is almost zero. So there is no base drive for transistor Q2 and it goes into cut-off and its collector...