What are the schemes of switching on transistors

Since the bipolar transistor is a classical three-terminal network, there are three possible ways of including it in an electronic circuit with one common input and output terminal:

• With common base (OB) - high voltage transmission ratio;
• With common emitter (OE) - amplified signal for both current and voltage;
• With common collector (OK) - amplified current signal.

In each of the three versions of the circuit of switching on the transistor, it reacts differently to the input signal, since the static characteristics of its active elements depend on the particular solution.

A circuit with a common base is one of three typical configurations for switching bipolar transistors. Usually it is used as a current buffer or voltage amplifier. Such circuits of switching on transistors differ in that the emitter here acts as an input circuit, the output signal is removed from the collector, and the base is "grounded" to a common wire. A similar configuration has circuitry for switching on the FET in amplifiers with a common gate.

The switching circuits of the transistors OB are distinguished by stable temperature and frequency characteristics, which ensures a small dependence of their parameters (transmission coefficient for voltage, current, input resistance) on the temperature conditions of the working medium. The shortcomings of the circuit include a small R _IN and a lack of current amplification.

A circuit with a common emitter provides very high gain and gives an inverted signal at the output, which can have a rather large spread. The transmission coefficient in this circuit largely depends on the temperature of the bias current, so that the actual gain is somewhat unpredictable. These switching circuits of transistors provide high R _IN , current and voltage gain, inverting of the input signal, convenience of switching on. Deficiencies include issues related to overexploitation - the possibility of spontaneous positive feedback, the appearance of distortions with small signals due to a low input dynamic range.

A circuit with a common collector (in electronics also known as an emitter follower) is one of three versions of the transistor switching circuit. In it, the input signal is fed through the base circuit, and the output is removed from the resistor in the emitter circuit of the transistor. Such a configuration of the amplifier stage is generally used as a voltage buffer. Here the base of the transistor performs the functions of the input circuit, the emitter is the output, and the grounded collector serves as a common point, hence the name of the circuit. Analogues can serve as schemes for the inclusion of field-effect transistors with a common drain. The advantage of this method is a rather high input impedance of the amplifier stage and a relatively low output.

All three typical circuits for switching on transistors are widely used in circuitry, depending on the purpose of the electronic device and the conditions for its use.