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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

TR2 is held cut off by the charge on C2 applied to its base and the unstable state is maintained during the time that C2 is discharging through R3 to the aiming voltage -Vc. This causes VB2 to rise exponentially towards cut-on. After a time determined mainly by the time constant C2R3, VB2 reaches cut-on and TR2 conducts. A second avalanche is thus initiated and the circuit 'flops' back to its original stable state in which TR2 is on and TR1 off. It will remain in this state until the next trigger pulse is applied to TR1 base.

We can see from Fig 4 that a very good negative-going rectangular wave is obtained from TR2 collector (Vc2). This is used as the output waveform. The p.r.f. is determined by the trigger rate, and the pulse duration by the time constant C2R3 (and the aiming voltage). Variation of R3 varies the pulse duration (or delay).


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