After the World War 2 (1948) the Transistor was invented in the Bell Laboratories in the USA (by Bardeen, Brattain and Shockley)
The First Transistor Colour Picture
Hearing Aids were the first commercial application of the new solid state invention (1952)
The First Transistorized Hearing Aid No I don’t Know how it was used
In 1954 the first transistor radio called the “Regency TR-1” was produced with the help from Texas Instruments It sold for about $49 which would be equal to over $300 dollars today
The First Transistor Radio Your Grandparents probably had one to listen to the new music that was just starting called Rock and Roll
So why are transistors so important. • They can be thought of as an electronic switch • The development of the transistor was the key component to the development of the modern computer. • Without the development of the transistor your home computer would look like..
In basic terms a transistor is a semi- conductor device made up of three separate parts • These parts are called the Emitter, the Base and the Collector
These parts are put together like a sandwich with the Base being between the Emitter and the Collector Emitter Base Collector
Origin of the names • the Emitter 'emits' the electrons which pass through the device • the Collector 'collects' them again once they've passed through the Base • ...and the Base?...
Transistors essentially consist of a pair of PN JunctionDiodes that are joined back-to-back. This forms a sort of a sandwich where one kind of semiconductor is placed in between two others. There are therefore two kinds of sandwich, the NPN and PNP varieties.
collector collector base base emitter emitter Schematic Symbols NPN transistor PNP transistor Notice the difference in the arrow head on the Emitter it always points towards the part (either the Base or the Emitter) that must be more negative for the transistor to turn on.
Transistors have 2 basic uses today • To amplify an input signal • To act as an electronic switch
When a transistor is used as a switch it uses the base voltage to turn the transistor on or off • By doing this a transistor can use a very low current and voltage to control a much higher current • When a transistor is turned on essentially the electrons flow straight from the Emitter to the Collector
In the next few slides we will look at how an NPN transistor is used to simulate a switch
Transistor as a Switch Transistor Switch • Transistors can either • conductornot conduct current. • ie, transistors can either be onoroff.
How Transistors Work Collector • Switching is controlled by the voltage between the Base and the Emitter. Base Emitter • When VBE < 0.7V the transistor switches off and • no current flows between the Collector and the Emitter. • When VBE ≥ 0.7V the transistor switches on and • current flows between the Collector and the Emitter.
When a Transistor is “turned off” . Which in the case of the NPN transistor is when the difference between the base voltage and the Emitter voltage is less than 0.7 Volts there is no connection between the Emitter and Collector (open circuit) • If you used a meter to measure the voltage difference between the Emitter and the Collector you would read all the voltage availible
When a Transistor is “turned on” . Which in the case of the NPN transistor is when the difference between the Base voltage and the Emitter voltage is more than 0.7 Volts there is a connection between the Emitter and Collector (closed circuit) • If you used an meter to measure the voltage difference between the Emitter and the Collector you would read approximiately 0.2 Volts
Base Thickness The thickness of the Base has to be just right. • Too thin, and the Base would essentially vanish. The Emitter and Collector would then form a continuous piece of semiconductor, so current would flow between them whatever the base potential. • Too thick, and electrons entering the Base from the Emitter wouldn't notice the Collector as it would be too far away. So then, the current would all be between the Emitter and the Base, and there'd be no Emitter-Collector current.
So what is the correct thickness of the base. This depends on the transistor and the amount of current it controls but on most transistors the base is only a micron to an atom in thickness. Why does it have to be so thin you ask