COMPUTING

Chapter 7 Pulse Circuits and Waveform GeneratorsV CCR AR Bv CCRR2 ⁄ 3 V CCComparator 1+R1 ⁄ 3 V CCS+Comparator 2QQT 1 T 2OutputRFigure 7.6. Implementation of an astable multivibrator with a 555 Timerv C = 2 ⁄ 3 V CCv C = 1 ⁄ 3 V CCT 1T 2Output waveformFigure 7.7. Input and output waveforms for the astable multivibrator of Figure 7.6When the capacitor reaches the value v C = 2⁄ 3 V CC , the output of Comparator 1 goes High andresets the SR flip−flop and thus the output Q goes Low, Q goes High, the transistor becomes saturated,its collector voltage becomes almost zero, and since it appears at the common node ofresistors R A and R B , the capacitor begins to discharge through resistor R B and the collector ofthe transistor. The capacitor voltage v C decreases exponentially with time constant t d = R B C7−4Electronic Devices and Amplifier Circuits with MATLAB Computing, Second EditionCopyright © Orchard Publications