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AP3302 Pt3 Contents

AP3302 Pt3 Section 2Contents

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AP 3302 Pt. 3

Section 2


Monostable and Bistable Multivibrators

 When TR1 conducts on application of the trigger pulse, its collector voltage Vc1 falls from the negative supply voltage level towards zero. This change in Vc1 is transferred instantaneously to TR2 base through C2 causing TR2 to conduct less heavily. Vc2 therefore rises towards -Vc and the common emitter voltage VE falls towards earth. (This occurs because the fall in current through RE due to TR2 is greater than the rise due to TR1 since the change of voltage at TR2 base has been amplified through TR1). The fall in VE causes TR1 emitter voltage to become more positive with respect to its base and TR1 conducts more heavily. The usual avalanche occurs to 'flip' the circuit into its unstable state in which TR2 is off and TR1 on.


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