What are the transistor switching circuits

2024 Author: Trinity Chesterton | [email protected]. Last modified: 2024-01-02 00:28

Since the bipolar transistor is a classic three-terminal device, there are three possible ways to include it in an electronic circuit with one output common for input and output:

• common base (CB) - high voltage transfer ratio;
• with a common emitter (CE) - amplified signal in both current and voltage;
• common-collector (OK) - amplified current signal.

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

The common base circuit is one of three typical bipolar transistor turn-on configurations. It is usually used as a current buffer or voltage amplifier. Such transistor switching circuits differ in that the emitter here acts as an input circuit, the output signal is taken from the collector, and the base is "grounded" to a common wire. FET switching circuits in common-gate amplifiers have a similar configuration.

Table 1. Mainparameters of the amplifying stage according to the scheme OB.

Parameter	Expression
Current Gain	Ik/Iin=Ik/I e=α[α<1]
In. resistance	Rin=Uin/Iin=U be/Ie

The switching circuits of OB transistors are characterized by stable temperature and frequency properties, which ensures a small dependence of their parameters (voltage, current, input resistance) on the temperature conditions of the working environment. The disadvantages of the circuit include a small R_{ВХand the lack of current gain.}

The common-emitter circuit provides very high gain and produces an inverted signal at the output, which can have quite a large spread. The gain in this circuit is highly dependent on the temperature of the bias current, so the actual gain is somewhat unpredictable. These transistor switching circuits provide high R_{IN, current and voltage gain, input signal inversion, easy switching. The disadvantages include problems associated with overamping - the possibility of spontaneous positive feedback, the appearance of distortion at small signals due to the low input dynamic range.}

Table 2. The main parameters of the amplifyingcascade according to the scheme OE

Parameter	Expression
Fact. current gain	Iout/Iin=Ik/I b=Ik/(Ie-Ik)=α/(1 -α)=β[β>>1]
In. resistance	Rin=Uin / Iin=U be/Ib

The common-collector circuit (also known as an emitter follower in electronics) is one of three types of transistor circuits. In it, the input signal is fed through the base circuit, and the output signal is taken from the resistor in the emitter circuit of the transistor. This amplifying stage configuration is typically used as a voltage buffer. Here, the base of the transistor acts as 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 be switching circuits for field-effect transistors with a common drain. The advantage of this method is a rather high input impedance of the amplifying stage and a relatively low output impedance.

Table 3. The main parameters of the amplifier stage according to the OK scheme.

Parameter	Expression
Fact. current gain	Iout/Iin=Ie/Ib =Ie/(Ie-Ik)=1/(1-α)=β [β>>1]
Coff. voltage gain	Uout /Uin=URe/(U be+URe) < 1
In. resistance	Rin=Uin/Iin=U be/Ie

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