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Application of Electricity to Transistors

Paper Type: Free Essay Subject: Physics
Wordcount: 1858 words Published: 8th Feb 2020

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A transistor is an electronic device that has three terminals where a small current at one terminal is used to control currents at the other terminals. Before transistors were invented by Bardeen and Brattain in 1947, thermionic valves (vacuum tubes) were the devices that were able to amplify current signals within a circuit. The vacuum tubes used the thermionic emission conception to emit heat to an element in vacuum emitted electrons to “attract” the signal flowing in the direction. As electrons were unable to travel in the opposite direction, vacuum tubes act as a diode. As vacuum tubes required lots of power, a heat supply and they carried flaws within the construction of certain electronic devices such as freezers that could be affected by thermionic emission.

As vacuum tubes had flaws, engineers John Bardeen and Walter Brattain invented the first field effect transistor in 1945 and the basic bipolar junction transistors in 1947. They were discovered at Bell Laboratories with the goal to replace vacuum tubes with the diode role and have low requirements to function.

Transistors are used to alternate signals and can have the role of a switch or an amplifier. Transistors compared to vacuum tubes, outweigh in advantages, which are;

  • No heat supply required
  • Very small in size, reducing equipment weight and size
  • Large amounts of transistors can be used to function as an integrated circuit
  • Low operating voltages required, compatible with batteries
  • Not susceptible to physical damage

As vacuum tubes can function as a transistor, they individually function as diodes, which can be also replaced with an electric diode. As diodes have the role to check valves of which are mainly to carry on and off operations, it is used to convert AC signals to DC signals. As both electric diodes and vacuum tubes carry the same role, vacuum tubes can be replaced with electric diodes as they have been outweighed in terms of statistics.

A diode is an electronic device which allows the signal to flow in one direction, blocking opposite directed signals. Diodes are used to create DC currents within a circuit, which can be used to power devices that require a constant current. This process is called rectification and it is the process of converting AC to DC. Though diodes are more complicated than just switching On-Off operations due to the non-linear behavior currents and voltages carry in the circuit.

Transistors and diodes work well to power specific devices when given a small signal. Using transistors to amplify signals, then using diodes to create a DC current, they cover different roles.

The two basic versions of transistors are the bipolar junction transistor (BJT). and the field effect transistor (FET). The two types of BJT are npn and pnp which stand for Negative Positive Negative and Positive Negative Positive. Both BJT transistors are meant for different purposes and have different functions which are required for specific necessities. The device consists of an active channel through which charge carriers, electrons or holes.

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Npn and pnp transistors are current controlled transisors that allow for current amplification or play as the role of a switch. How both versions differ is how power must be allocated to the terminal pins to provide amplification or switching. An npn transistor receives positive voltage to the collector terminal and positive voltage to the base terminal for proper operation. A pnp transistor receives positive voltage for current to flow into the base. Then a lower voltage is supplied to the emitter terminal.

Both diagrams for PNP and NPN transistor from http://www.learningaboutelectronics.com/Articles/Difference-between-a-NPN-and-a-PNP-transistor


FET and their importance

Field Effect Transistors are considered ‘Voltage Operated Devices’ and are divided into two main types; Junction-gate devices and Insulated-gate devices, or more commonly known as Metal Oxide Semiconductor FET (MOSFET). The junction gate FET is the simpler field effect transistor, it has to ability to either pass from source to drain or drain to source. JFET uses the voltage applied to control the current which outcomes the output signal to being proportional to the input voltage.

The metal oxide semiconductor FET is a four terminal FET which has controlled oxidation of silicon which makes the MOSFET more reliant to temperature and voltage increases compared to the JFET.

Field effect transistors are the most common transistors in electronic circuits because or their voltage controlled semiconducting abilities that are used to amplify weak signals using the electric field effect.


How is a transistor made? In depth analysis

Transistors are created using silicon, a substance component found in sand, which does not typically conduct electricity (it doesn’t allow electrons to course through it effectively). Silicon is a semiconductor, which means it’s neither a conductor nor a resistor. If silicon is treated with impurities (a process known as doping), it can behave in a different way. If silicon was ‘doped’ with chemicals such as arsenic, phosphorus, or antimony, the silicon gains some additional “free” electrons—ones that can carry an electric signal—so electrons will stream out of it more easily. Because electrons have a negative charge, silicon treated this way is called n-type (negative type).  Silicon dope with other impurities such as boron, gallium, and aluminium. Silicon with this treatment do not have as much “free” electrons meaning electrons in nearby materials to follow into it. this silicon is called the positive type.

Comprehensive explanation of what the transistor does and how it works

The two main roles of a transistor is to work as an amplifier, or as a switch. When working as an amplifier, it takes in a small electrical signal at one end (at the receiver) and produces a much larger current as an output. When transistors were first invented, their main use was to make hearing aids, as the mechanism of a hearing aid is to use a small mic to pick up low volume of noise, and boost it using transistors.

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Transistors also have the role to work as a switch. A small electric signal can flow at one part of the transistor, making a much bigger signal flow through another part of it. This work is how memory chips work as well. A memory chip contains hundreds of millions of transistors, which are switched on and off individually, all with the role to store two different numbers, one or zero. A chip containing billions of zeros and ones are read and are written by computer software’s.

Exemplar of how transistors are used within devices.

Transistors are used in devices and currents to mainly amplify currents or to be used as a switch to turn currents on or off. When transistors are used as switches, they are used to keep currents fully off or fully on using transistors and diodes. The most common transistor switch is using the NPN transistor to keep circuits fully on or off.

From https://www.electronics-tutorials.ws/transistor/tran_4.html

In the diagram above, an npn transistor is used as a switch to keep the current either fully on or fully off. This is because of how when the input of the transistor meets a certain current requirement, the signal will be amplified and go towards the positive output of the terminal. If the input does not have the required amps, the whole signal is brought down and left at 0. This can be used as a memory chip because of how it keeps memory of either OFF or ON or more commonly known as 0 and 1, (binary language read by computers to alternate data within its software).

As this only stores 1 bit of information, computer engineers have further developed on transistors to build more within a circuit to store 32 bits of data using a 4×3 memory chip consisting of 12 transistors.

In this circuit, 3 output signals travel and amplify data sets of these memory chips which hold 8 bits of data every row. As transistors work together to store more information, data stored can be red by a decoder to be read as words. If this was applied but replaced the npn transistors with vacuum tubes, the circuit will be significantly larger, it will require a heat source that consumes a large amount of electricity, and stress within the signal will occur due to large amounts of heat within all transistors due to thermionic emission.

Conclusion, and your finally done bro


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