Page 1132 - Basic Electrical Engineering

Figure 17.11 (a) IC 555 timer in monostable operating mode; (b) waveforms of voltages in
monostable operation

17.7.5 Astable Application of IC 555

For astable application, the external connection of the timer has been shown

in Fig. 17.12. In astable application, the output will alternate between two
states, i.e., high and low automatically and continuously without any trigger

pulse.
Here, both the trigger input and the threshold input are connected to the
capacitor. An additional resistance R has been connected between the
1
capacitor and the discharge transistor to slow down the discharge of the

capacitor. When the capacitor discharges to V , the comparator B (i.e., the
CC

trigger comparator as shown in Fig. 17.10) sets the flip-flop which in turn
switches the discharge transistor off, allowing the capacitor getting charged