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14-5 Using the Multivibrator:

It is well known that in every TV receiver there is a horizontal oscillator and a vertical (vertical) oscillator. These oscillators direct the electronic beam to scan the screen with a number of lines per second, equal to the horizontal frequency and a number of fields equal to the vertical frequency. .

One of the types of oscillators used is the multivibration oscillator, whether it is a valve or a transistor. The principle of these oscillators is based on two amplification stages connected by
​​​​​Resistors so that the output of the second amplifier is connected to feed in reverse the input of the first amplifier, thus achieving the work of the oscillator - and the values ​​of the resistors and capacitors determine the frequency of this oscillator.

Transistorized Multivibration Oscillator In the diagram (Fig. 14-5), we find that the two transistors work as a multivibration oscillator and may be used in the horizontal and vertical deviation stage. Vibration is achieved because it connects the complex of Q1 with the base of Q2 - and the feedback from the complex of Q2 to the base of Q1 - and the two transistors are of the type PNP, the transistor PNP cuts off when the base becomes positive for the emitter - both capacitors C2-3 are discharged through the base bias resistance (4) or R5 generates cutting effort and makes

​​​​​The two transistors are in the cut-off state, and the duration of the cut-off for them is determined by the time constant RC to connect the resistors and capacitors R4-C3 or RS-C2. The following specifications must be met in the circuit of the multivibration transistor amplifier. This applies to the common radiator method, because there is a phase shift of 180 m between the signal's output and its input.

An increase in the base current causes an increase in the collector current in the transistor. Conversely, the base current decreases due to the collector current decrease.

2- An increase in the collector current causes a decrease in the collector voltage - and a decrease in the collector current causes its voltage to rise to the value of the source voltage. PNP transistors increase the collector current and make its voltage less negative. NPN transistors make the collector voltage less positive.

3 - In the normal operation of the transistor amplifier - the dual-base bias - the emitter is forward and the base collector is reverse biased - and the polarity is determined according to the type of transistor used (PNP or NPN).

4 - The transistor reaches saturation when the additional increase in the base current does not cause any additional increase in the collector current.

circuit work:

The free-running multivibrator is essentially a non-sine wave. The oscillator has two stages, one of which is in the connected state while the other is in the cut off state, then the inversion between the two stages begins. Where the interrupting circuit is connected and the connecting circuit is interrupted, and this oscillation usually generates a square wave at its output. Most of the transistors of the multivibration oscillator circuit are analogous to the analogous valve circuit. The one connected to the radiator is similar to the one connected to the cathode. If the work of the valve circuit is clear, the transistor circuit similar to it can be accommodated.