multivibrator astable


Posted on Feb 7, 2014

The astable multivibrator is a unique form of the relaxation oscillator in which the in-phase feedback is provided by a separate transistor. The first multivibrator was built with vacuum tubes and the circuit was very popular from the start. Millions were built and used in the earliest computers and employed in TV sets in their sweep generation an


multivibrator astable
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d deflection circuits. Multivibrators generate rectangular waveforms that can also be used for timing generator applications. There is often a need to have a clock oscillator when working with digital logic. Most often complete IC (Integrated Circuit) modules are used or some logic gates for that purpose. Making the clock oscillator from available spare transistors and a handful of surplus parts not usually done because of needless worry of possible circuit complexity. As demonstrated here the circuit is quite simple and it is very easy to customize it for the application at hand. Almost any transistor available is useable in this circuit if the selected frequency for oscillation is not very high. With the values as indicated on the schematic diagram the oscillators frequency is 1 kHz and the cycle time is mSec (mili-Second). With the circuit operating from a 5-volt power supply the output voltage is acceptable to drive TTL and CMOS gates directly. The actual multivibrator oscillator circuit is made up of transistors Q1 and Q2 only for its operation - Figure 1. To be able to obtain the signal from this oscillator without changing its frequency with the external load, transistor Q3 is added as a buffer output amplifier stage. The Q3 transistor isolates the multivibrator and this stage has no voltage gain as it is used for impedance transformation. Transistor Q3 provides low impedance output for the load while presenting high...




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