Transistor As Switch Amplifier


The transistor is the kind of service that works in an active region, the transistor acts as an amplifier and in case it acts as a switch it tends to perform in various cutoff and saturation regions. In the transistor that is working in the cutoff state, both the collector base and the emitter-base junctions are reverse biased. The transistor can act as a device, switch and amplifier. All these aspects accumulate to provide a service in multiple regions for example transistor as an amplifier is useful in the functionality of the optic fibers and is also useful in amplification of radio signals and other wireless communications.

What is a transistor?

Figure 1: Transistor as a switch

Transistors are generally used in multiple sections that help devise various applications. Transistors can act as a device that will be used in the form of a switch especially when it functions in the cut-off region, that is, the open switch and the case of the saturation region, that is, the closed switch. As opined by chamarchia et al. (2020), in another case, transistors are used in the form of an amplifier that enhances the magnitude of the output signal as it continues to operate in an active region. A transistor functions as a switch as it drives back and forth between the cut-off regions and saturation regions .

The transistor enhances the amplitude of the input signal. The signals of smaller amplitude are fed to the amplifier which in turn enhances it to derive the output large signals.

Transistor as a switch

If the transistor is utilized as a switch, the 2 operating regions that are formed are the cut-off region and the saturation region. At the cut-off region the transistors remain totally OFF and at the saturation region the transistors remain ON fully.

Region of saturation

In the region of saturation, the transistor gets the maximum current when IB is applied to it and this maximum amount of current is obtained at the IC collector. As the current in this region is maximum, and the voltage that is present in the collector is minimum. Thus, in this situation, the transistor is determined to be ON fully.

Figure 2: Transistor as a switch

The cut-off region

In the cut-off region, the current does not flow through the transistor. Here the base current that is IB remains zero and the current in the IC collector, also remains zero. As in both cases, the current value is zero, and the voltage of the collector that is VCE is maximum, which results in a large layer of depletion.

Transistor as a switch: applications

The main applications of transistors as switches are mentioned below.

  • The function of LED is one of the major examples of the transistors as switches.
  • The working of DC motors can be controlled by the application of various values to the motors’ speed and is further4 used in case of turning the motors ON and OFF (Chauhan et al. 2018).
  • The resistor that usually depends on the rays of light uses the transistors as switches.
  • The transistors as switches is also used in the low voltage lamps that have digital IC or logic gates: OR gates and AND gates.

Transistor as an amplifier

The emitter mode is considered to be the common mode of connection. In using a transistor as an amplifier the performance of the amplifier becomes vital. The amplifier basically performs the phenomenon like Input resistance, Output Resistance, Voltage gain, Current Gain, and Power Gain.

Figure 3: Transistor as an amplifier

Amplifier performance

In the case of Current Gain, the ratio of the current change in collector and change of the base current is measured. In the Voltage gain, the ratio of input and output voltage is measured. In Power Gain, the ratio of output signal and input signal of powers are measured (Cheng et al. 2017). Input resistance, measures the ratio of a slight change in emitter-base voltage and change in base current by keeping the emitter-collector voltage constant. Output Resistance, is the measurement of the ratio of change in emitter-base voltage and the change in collector current by keeping the base current constant.

Transistor as an amplifier: applications

The main applications of transistors as an amplifier are mentioned below.

  • In the case of optical fiber communication the transistor are often used as an amplifier. This is because the output signal is high and can be applied in the long-distance communication channels.
  • The transistors as an amplifier are also used in radio signals and wireless communications.
  • The implications of audio can be possible if the transistor is used as an amplifier.
  • The transistors as an amplifier are generally used in the electronic and communication field.


The transistor is the kind of device that has multiple applications and functionalities. These devices are useful as an amplifier, switches or a device. These transistors enhance optical fibre works. As the output signal is high therefore transistor as an amplifier is useful in long-distance communication. These amplifiers are also useful in the case of audio amplification. In this cut-off region, these transistors act as a switch when it operates for resistors that are dependent on light. Therefore it can be established that transistors functions as various units and serves multitudes of functions in daily life.


Q1. What are the applications of switch transistors?

The applications of LED are one the crucial examples of transistors that act as a switch. A transistor as a switch is also used in DC motors and is controlled by different degrees of the speed of the motor. The solely light-dependent resistors also use the functionality of transistors as a switch.

Q2. What are the applications of transistors as an amplifier?

The amplification of radio signals is calibrated by these amplifiers; these amplifiers enhance the audio amplification process. The transistor amplifiers enhance radio signals.

Q3. What does it mean for transistors to be in cut-off regions?

The transistors mainly lie n the cut-off region because of a lack of flow of current through the transistor. This implies that the base current and collector current are both zero.

Q4. What does it mean for a transistor to be in a saturation region?

A maximum amount of base current is applied to the transistor in this region that derives maximum current at the collector. The voltage at the collector is at minimum because of the maximum flow of current.


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