[Physics Class Notes] on Transistor as a Device Pdf for Exam

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.