Monday, April 25, 2011

Astabil Multivibrator

Multivibrator is a relaxation oscillator type. This circuit uses the RC network and the region contribute to the square wave output. Astabel multivibrator used in the TV receiver to control the electron beam on the picture tube. In this series of computers used to develop the pulse time.

Astabil Multivibrator circuit


A multibrator consists of two cross-coupled amplifier. The amplifier output is one connected to another amplifier wedding. Because each penguata reverse input signal, the combined effect of this is in the form of positive feedback. With the feedback posotif, the oscillator will always get the extra energy (regenerative) and produces a continuous output.

The picture above shows the multivibrator circuit using 2 pieces of bipolar transistors with common emitter configuration. R1 and R2 provide bias voltage developed at the base of each transistor. Holding capacitor C1 to the base collector Q1 Q2. Q2 together with capacitor C2 to the base of Q1.

Because of this cross coupling, a transistor will be conductive and the other is the cutoff. The two transistors alternately will live and die so that the outputs are labeled Q or. That output has a polarity reversal.

When the power given to the multivibrator, one transistor will berkonduksi first, let us assume here that berkonduksi Q1 first. With Q1 berkonduksi voltage on R and Vc decreased, so that its value is lower than VCC. As a result akn happened to the negative voltage on C1 and the positive base voltage of Q1 will decrease. Q2 conduction is reduced and the collector voltage equal to VCC. Voltage will be towards the positive on the C2. This voltage is added to the base of Q1 and make it more berkonduksi. This process continues until reaching saturation point Q1 and Q2 to reach the cutoff.

Multivibrator device functioned as a trigger (triggered device) or free-running. Multivibrator trigger requires the input signal / pulse. Multivibrator output is controlled or synchronized by the input signal.
When the output voltage of each transistor achieve stability, then there is no voltage feedback. Q2 will return berpanjar forward through R2. Conduction in Q2 will lead to a decrease in VC. Voltage to the negative direction will be given on the basis of Q1 through C2. Q1 conduction is reduced. Vc in Q1 will rise worth with Vcc. This will tergandeng to the base of Q2 through C1. This process continues until Q2 Q1 reached saturation point and reach the cutoff. The output voltage then becomes unstable and the process will be repeated.

The frequency of oscillation of the multivibrator time constant distentukan by R2 and R3 and C1 and C2. The R2 and R3 are chosen such that each transistor can reach saturation point. C1 and C2 is selected to obtain the desired operating frequency. If C1 = C2 and R2 = R3 then the output will be symmetrical. Means that both transistors will live and die in selag the same time.

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