Posted on Feb 3, 2013    9094

You can obtain well over 360° of phase delay by cascading two monostable multivibrators. In a typical configuration, a single monostable multivibrator is used to introduce delay in a pulse train; the multivibrator triggers on each incoming pulse, provided it resets in time for the next pulse. Yet even when it resets in time, the single monostable multivibrator provides a maximum phase delay of less than 360°. However, with the cascaded-multivibrator approach, you can achieve 650° of phase delay by using an input-pulse spacing of 200 p.s for example, with the component values shown. Every input pulse will trigger the circuit while you adjust the phase delay throughout its available range.

Adjustable-delay - schematic

The first multivibrator triggers the second one, whose reset marks the total delay time (21). Each introduces a delay oft p.s, based on 0.01-p.F timing capacitors and equal charging currents from the three-transistor, dual-current source. The two multivibrator arrangement allows the first multivibrator to reset in time to be triggered by the next input pulse. Also, the variation of t is linear with the potentiometer setting.

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