What is a Transistor?
＜History of Transistors＞
The Transistor was Invented in 1948 at Bell Telephone Laboratories
The invention of the transistor was an unprecedented development in the electronics industry. It marked the beginning of the current age in the electronics sector. After the transistor's invention, advances in technology became more frequent, the most notable of which was computer technology. The three physicists who invented the transistor; William Shockley, John Bardeen, and Walter Brattain were awarded with the Nobel Prize. Considering the inventions that the transistor paved the way for, one could argue that it was the most important invention of the twentieth century.
From Germanium to Silicon
Transistors were originally manufactured using Germanium. This was the standard for the first decade of transistor production. The Silicon-based transistors that we're used to seeing today were adopted because Germanium breaks down at 180 degrees F.
Functions of a Transistor
A transistor's functions consist of amplification and switching. Let's use a radio as an example: the signals that the radio receives from the atmosphere are extremely weak. The radio amplifies these signals through the speaker's output. This is the "amplification" function.
For an analog radio, simply amplifying the signal will cause the speakers to produce sound. For digital devices, however, the waveform of the input signal needs to be changed. For a digital device like a computer or MP3 player, the transistor needs to switch the signal state to a 0 or 1. This is the "switching function"
Even more complex components like Integrated circuits made from Liquid Silicon Infiltration are basically collections of transistors.
Resistors and Transistors on a Single Chip
Originally, discrete resistors and transistors were mounted on the same printed circuits boards.Later on, transistor chips with built-in resistors were developed as digital transistors.Using digital transistors in designs has :
1.They require less area to mount components on a printed circuit board.
2.They require less time to mount the components on a printed circuit board
3.This reduces the number of components needed.
The first transistors with built-in resistors were developed by ROHM, who was awarded the patent rights. Digital transistors are also covered by one of ROHM's exclusive patents.
How Does a Transistor Work?
One analogy that helps explain how a transistor operates is to think of it like a water tap. In this case, electrical current works like water. A transistor has three pins: the base, the collector, and the emitter. The base works like the tap handle, the collector is like the pipe that feeds into the tap, and the emitter is like the opening where water pours out. By turning the tap handle with a small amount of force, we can control a powerful flow of water. This water flows through the pipe and out of the opening. Turning the tap handle slightly can dramatically increase the rate that water flows. If closed completely, no water will flow. If opened completely, water will gush out as fast as possible!
Now we can dive into a proper explanation using the diagrams below. A transistor has three pins, the emitter (E), the collector ( C ), and the base (B). The base controls the current from the collector to the emitter. The current that flows from the collector to the emitter is proportional to the base current. The emitter current, or base current = hFE. The setup shown uses a collector resistor (RI). If a current of Ic flows through RI, a voltage across that resistor will be formed, which is equal to the product of Ic x RI. This means that the voltage across the transistor equals: E2 - (RI x Ic). Ic is approximately Ie, so if IE = hFE x IB, then Ic also equals hFE x IB. Therefore, through substitution, voltage across transistors (E) = E2 (RI x le x hFE). Essentially, the input voltage E appears at the output after being converted into a voltage of IcRL.
(*1) hfe: DC Current amplification factor of the transistor.