Bradley 233 - Page 20

4.1. 6 Monostable (Waveforms : Fig. 4)
In the quiescent state pins 13, 12 and 9 of IC30 are in the low state. A trigger pulse at pin 13
drives pin 9 into the high state, which drives pin 12 through C31. The high state at pin 12
holds pin 9 through gate action. The trigger pulse is narrower than the minimum pulse width
of lC30c, but is wider than the gate propagation delay, to allow latching of pin 12.
The voltage at pin 12 then decays at a rate dependent on the current through R31 and the value
of C31, until it reaches the threshold. Then positive feedback through C31 causes pin 9 and
12 to snap down together until pin 12 is caught at the low level by the output emitter of pin 14.
Pin 9 continues the rest of the way to the low level at a rate dependent on the current in R32,
and the value of C31. This ramp determines the recovery time. If the monostable is triggered
during this recovery time, the output will be a narrower pulse than normal.
1C20, 40 and 60 work in a similar fashion, but 1C40 can be switched to an astable multi
vibrator mode.
The circuit of 1C60 differs in being triggered directly at the
INPUT TRIGGER
10 30 PIN 13
PIN 12
OUTPUT
PIN 9
I,
FIG.4 MONOSTABLE WAVEFORMS
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