Pulse and Digital Circuits

8.2 COLLECTOR-COUPLED MONOSTABLE MULTIVIBRATORS

The collector-coupled monostable multivibrator is shown in Fig. 8.1. When compared to an astable multivibrator as shown in Fig. 7.1, it is evident that the output from the second collector to the first base is through a resistance R₁. Hence, this circuit has one stable state and one quasi-stable state.

As a negative voltage is connected to the base of the first device, it is possible that Q₁ may be OFF. In the stable state, let Q₁ be OFF and Q₂ be ON and in saturation. Therefore:

 

V_C1 = V_CC    V_C2 = V_CE(sat)    V_B2 = V_BE(sat) = V_σ

The capacitor, C now tries to charge to V_CC through R_C of Q₁ and a small input resistance of Q₂, as shown in Fig. 8.2. As t→∞, this voltage reaches V_CC. To change the ...