Courses
Courses for Kids
Free study material
Offline Centres
More
Store Icon
Store

Transistor as a Device

ffImage
Last updated date: 23rd May 2024
Total views: 426k
Views today: 9.26k
hightlight icon
highlight icon
highlight icon
share icon
copy icon

What is Transistor?

Transistor is a three-terminal electronic component. It has a control (“gate”) terminal, a collector terminal and an emitter terminal. Current flows through the emitter to the collector in one direction, and it can be interrupted by using the control terminal. An NPN transistor turns on or off in response to a positive voltage applied to its control terminal. A PNP transistor turns on or off in response to a negative voltage applied to its control terminal.


The transistor is a component in a semiconductor circuit. When the transistor is in the ON state, the circuit is ON, and when the transistor is in the OFF state, the circuit is OFF. shows a simple transistor circuit that controls the power supply to the circuit (ON when the base-emitter junction is forward biased, OFF when the base-emitter junction is reverse biased). The circuit has four transistors. The ON/OFF state of the circuit can be controlled by using the collector terminal as the output. For example, the ON state controls the circuit output to be in the high level (ON) state, and the OFF state controls the circuit output to be in the low level (OFF) state.


Transistor technology has been used in electronics and computing since the 1920s. At least one transistor was invented in 1933 by two scientists working independently, William Shockley and John Bardeen. The invention was the first practical device for amplifying or switching a flow of electricity in an electronic circuit. The first working devices were silicon transistors, invented by Julius Lilienfeld and Walter H. Weber at Bell Labs, New Jersey. The first working solid-state transistor was the germanium junction transistor invented by Philo Terman and Jack Kilby at Texas Instruments. This was followed shortly by several other working devices. In the 1950s, transistor technology reached the semiconductor industry where transistors began to be used in computers and other devices.


Transistors in a device

A transistor is a semiconductor device with two major parts. The first is the collector, which collects the current. The second part is the emitter, which supplies the current. These two parts are separated by a layer of dielectric material called a junction or barrier. The most common junction or barrier is the p-n junction between the region of the semiconductor that is p-type and the region of the semiconductor that is n-type.


The transistor can only pass current when a voltage is applied across the collector and emitter. Current cannot flow from the emitter to the collector in the absence of a voltage applied across the emitter and collector. The semiconductor used in the transistor must have the ability to pass current only when a voltage is applied across the semiconductor. In the absence of a voltage applied across the semiconductor, the current is stopped.


Transistors pass or amplify a current because they have a very small resistance when they are switched on. The resistance is usually very small and is given by the ratio of the current when the transistor is switched on to the current when the transistor is switched off. The term resistance is usually given to the resistance of the dielectric layers between the collector and emitter. As the size of the transistor is increased, the resistance of the dielectric layers tends to be reduced.


If the resistance of the dielectric layers between the collector and emitter is reduced below the resistance of the transistor when the transistor is switched on, the collector current is amplified. The resistance of the transistor when the transistor is switched on is given by this ratio. If the transistor has been properly designed, the resistance when the transistor is switched off will be very small. If it is very small, then the resistance when the transistor is switched on will be much larger. The resistance when the transistor is switched off is given by the voltage across the collector and emitter when the transistor is switched off. The voltage is divided by the emitter current and the ratio of the voltage divided by the emitter current is the resistance of the transistor when the transistor is switched off.


The base currency is the current that flows from the base to the emitter. The emitter current is given by the ratio of the current when the transistor is switched on to the current when the transistor is switched off. This ratio is the transistor's amplification or gain. The collector current is given by this ratio of the current when the transistor is switched on to the current when the transistor is switched off. The resistance of the transistor when the transistor is switched on is given by the voltage across the collector and emitter divided by the emitter current. The voltage is multiplied by the ratio of the emitter current to the collector current.


Summary

Voltage is the difference in electric potential between two points on a conductor. Voltage is defined by the amount of work done to move electric charge from one point on the conductor to another. Voltage is measured in volts or volts per amp. Current is the flow of electric charge past a conductor. Current is measured in amps or amps per centimeter. Resistance is the ratio of the voltage divided by the current.  


Voltage is measured across the terminals of a component. Amperage is measured across the terminals of a component. Current is measured across the terminals of a component. Resistance is measured across the terminals of a component.

FAQs on Transistor as a Device

1.What is a transistor?

A transistor is a semiconductor gadget that moves a powerless sign from a low opposition circuit to a high obstruction circuit. The words trans mean exchange property and transistor mean opposition property offered to the intersections.

2.How to memorise physics concepts for a long time?

Physics is a natural science that is all about the study of matter around us, its behaviour and its application. It is basic physical science.  Students can make mind maps and write down formulae for better understanding and it also helps in retaining the concepts for a longer period. At Vedantu, we provide revision notes and keywords which would help students in saving time in preparing the notes and assist them in chapter wise revision. 

3.How to manage time while writing a physics exam?

Many students say that though they went prepared to give their physics exam, due to the lengthy and tricky questions, it became difficult. To avoid such an experience students are recommended to practice writing faster and memorising the keywords. Also working out objective type questions beforehand saves time in analysing and answering them. Lastly, students are advised to divide their time into sections namely A, B, C and D and attempt all the questions without fail.

4.Explain in nutshell the Transistor?

Since we all know that a transistor has 4 regions of operation, commonly in which Active cut-off and Saturation are used.  When a transistor works in an active region the transistor acts as an Amplifier and when it works as a Switch it works in Cutoff and Saturation Regions. The transistor in a Cutoff State both collector base and the Emitter base junctions are reverse biased.  Whereas in the saturation region both junctions are forward biased.  


Most of the digital IC’s transistors will work as a switch to make power consumption very low. It is also a very useful circuit for an electronics hobbyist as it can be used as a driver, inverter etc. The transistor when utilized in the cutoff or immersion state, goes about as a switch and afterward worked in the active region is utilized as an amplifier.

5.What are the different conditions for using a Transistor as a Switch?

There are various conditions that need to follow while using the transistor as a switch. In simple words, we can also say that there are various essentials for using the transistor as a switch. Following are the conditions applied when you use a transistor as a switch  Transistor switches can be used to control lamps and switches, relays or even motors.


When you use the bipolar transistor as a switch they must be either “fully-OFF” or “fully-ON” Those transistors that are fully “ON” are called to be in their Saturation region Transistors that are completely “OFF” are called to be in their Cut-off region When you use the transistor as a switch, a very small Base current controls a much larger Collector load current When you use transistors to switch inductive loads such as solenoids and relays, a “Flywheel Diode” is used When large voltages or currents need to be controlled, Darlington Transistors can also be used.

Students Also Read