What is a Transistor?

Transistor are electronic circuit elementsthat are technically used to control a voltage or current source and another current or voltage source. BJT and FET's are frequently used transistors. Those who work with the current fall into the BJT class, while those who work with the electric field generated by the voltage fall into the FET class. More FET is used in integrated digital circuits. Transistors have three legs. These legs are Base, Emitter and Collector in BJT, while FET is known as Gate, Drain and Source.

Transistors are divided into 4 transistors, "Point contact" and "Surface contact" transistors, transistors made by "Alloy method" and "Alloy propagation".


History of the Transistor

The thermoonic triage (a.k.a. lamp or vacuum tube) was invented in 1907 and thus played an important role in the formation of inventions such as radios and telephones. But the lamps consumed a lot of electricity, they were overheating and could easily break down.

The first patent for the transistor was filed in Canada on October 22, 1925 by Julius Edgar Lilienfeld, an Austrian-Hungarian physicist. Lilienfeld wanted to obtain this patent for the first field-acting transistor (FET), which can be used instead of vacuum tubes. However, their work was rejected by the industry because no research papers were submitted and there were no working samples or prototypes. In 1934, German inventor Oskar Heil filed a patent for a similar transistor in Europe.

Between November 17 and December 23, 1947, John Bardeen and Walter Brattain conducted various experiments at AT&T's Bell Laboratories in New Jersey, USA. In one of these experiments, they observed that the output of the signal applied to the two golden contact points on the germanium crystal was higher than the inlet.

The first transistor prototype to work.

The transistor's name is John R. It was presented by Pierce as an acronym for "transresiztans", which we can think of in terms of transitive resistance.

How Transistors Work

Transistors are examined according to their working regions. The working regions of the transistor are called cutting, saturation and active regions. Transistor; performs key function in the cutting and saturation zones. Especially in the design of digital systems, this feature of the transistor is used and used as a key. Another very commonly used feature of the transistor is its use as an amplifier. A transistor to be used as an amplifier is operated in the active zone.


In order to understand the basic principle of operation of the transistor, it is appropriate to explain it in an example. In the picture above you see a faucet. Let's compare the handle of this tap, which allows us to turn water on and off, and at the same time adjusting its speed, to the Base of the BJT transistor and the Gate end of the FET transistor. The force we apply to the handle adjusts whether the water flows (you can think of it as a current) or how quickly (you can think of it as current intensity).

When we do not apply a force to the handle, it prevents water (i.e. current) from flowing due to its mechanical structure inside (you can think of it as electronic resistance). In this case, consider that the part where the water enters the tap is the Collector leg in BJT transistors and the Source leg in FET transistors. The part where the water comes out of the tap is emitter in BJTs and Drain leg in FET's. We can also think of the drain of water as soil.

Transistor Types and Structures


The most commonly used transistor types in hobby electronics are bipolar junction transistor (BJT) and metal-oxide semiconductor field efect transistor (MOSFET). The transistor in the example we used when describing the working principle of the transistor above is a BJT of type NPN.

BJT (Bipolar Junction Transistor)

Legs of an NPN-type transistor.

These transistors are called "bipolar articulated transistor"in Turkish. The BJT expression consists of the initials of the English Bipolar Junction Transistor. BJT transistors are the most widely used transistor.

BJTs have 3 legs: collector, emitter and base:

What is MOSFET?

Legs of an N-type MOSFET.

The word MOSFET stands for Metal Oxide Semi-conductor Field Effect Transistor,which means metal oxide semiconductor field effect transistor, developed types of field-effective transistors (FET). They can be used for switching and power balancing in analog and digital circuits. As with BJTs, MOSFETs have 3 legs. These legs are named gate, drain and source.

Bipolar transistors are of two types: NPN and PNP according to the semiconductor sequence in their structure.

What are NPN and PNP? What's the Difference?

In order to understand the terms PNP and NPN, which are mentioned a lot especially in automation electrical and electronic technologies, and to know the difference between the two, let's first talk about transistor technology. Transistor is one of the most commonly used controlled switching elements in power electronics circuits. All electronic equipment used in our daily life includes transistors. The structure of the transistor, a three-legged semiconductor element, resembles two diodes connected back to back. The collector is the legs of the base and emitter transistor. There are two types of transistors, PNP and NPN.


NPN Transistor:

– NPN type transistors also start flowing from Collector to Emitter if the base voltage is higher than emitter voltage. – A very small amount of current flows from the base end to the Emitter end.

PNP Transistor:

– PNP type transistors also start flowing from Emitter to Collector if the base voltage is lower than emitter voltage. – A very small amount of current flows from emitter end to base end. Sensors generally have three cables. One of them is positive, one is negative and the other is the signal, the output end. Below is a diagram of the connection of cable ends and loads of PNP and NPN sensors. • NPN sensors are sensors with a negative tip switched. So when the sensor sees the object in front of it, the output is negative. • PNP sensors are sensors with a positive tip switch. So when the sensor sees the object in front of it, the output is positive. In the above description, it was explained that the output ends are positive and negative. However, the important thing to note here is not to confuse PNP and NPN sensors with NC and NO. NO and NC (normal on and off normally) are separate.