Birth of Transistors

Before the advent of transistors, vacuum tubes were used in all electronic circuits for different purposes. Even though they did serve their purpose they had a few disadvantages that like the huge size high power requirements. This lead to the calling for a better, smaller, and more efficient component as a result of which the transistor was born.

Three individuals William Shockley, John Bardeen, and Walter Brattain on December 23, 1947 at Bell Laboratories Murray Hill, New Jersey launched the first-ever TRANSISTOR. Bell Labs is the research arm of American Telephone and Telegraph (AT&T).

Transistors are electronic devices that are commonly used to amplify or switch electrical signals. They are made up of three layers of a semiconductor material, such as silicon, with each layer having a different electrical charge. The three layers are known as the source, the drain, and the gate.

Transistors operate on the principle of a voltage or current being applied to the gate, which in turn controls the flow of current between the source and the drain. This allows transistors to act as amplifiers, increasing the strength of a weak electrical signal, or as switches, turning the flow of current on or off.

Transistors were first developed in the 1940s, and have since become an essential component of modern electronics. They are used in a wide range of electronic devices, including computers, smartphones, and other electronic devices.

There are two main types of transistors: bipolar junction transistors (BJTs) and field-effect transistors (FETs). BJTs have three layers of semiconductor material, with the source and the drain being doped with different types of impurities to create p-type and n-type semiconductors. The gate is usually made of a metal or a heavily doped semiconductor.

FETs, on the other hand, have only two layers of semiconductor material, with the gate being separated from the source and drain by a thin layer of insulating material. This allows the gate to control the flow of current between the source and the drain by creating an electric field.

Transistors have a number of important characteristics that make them useful in electronic devices. These include their small size, their low power consumption, and their high switching speeds. Transistors are also able to operate over a wide range of temperatures and frequencies, making them versatile and reliable components of modern electronics.

Transistor Types

Through-Hole Transistors

Through-hole transistors have component legs that are inserted through the holes on a PCB and then soldered in place. They are currently used in high power applications and are less common than they were in the previous century.

TO-92 Package Transistors

The TO-92 package is one of the most common packages for through-hole transistors in the past and is still a very popular package in prototyping and hobby circuits. TO-92 packages have a curved face and a flat face where the part number is printed. It has packages with have their leads very close together which make them more difficult to insert into a PCB if a standard 0.1” pitch is used

T0-92

Application of T0-92

TO-220 Package Transistors

The TO-220 is another common transistor package with wide application in medium power amplification and switching doamins. The TO-220 package has a tab on the top of the part that is used for mounting onto which a heat-sink maybe mounted horizontally or vertically directly onto the PCB.

The voltage regulators including the LM series also tend to use T0-220,hence extra care has to be used while selection of the T0-220.

TIP32C PNP Bipolar Power Transistor 100V 3A TO-220 Package, DIP, | ID:  22375810430
PNP Bi-Polar Transistor

TO-3 Package Transistors

They are widely used in high-power/high-current situations and their prices range from low to expensive. This package has three connections. It has two pins for connection purposes and the body is the third connection.

The package has two holes for mounting directly on to a heat sink and the part number is printed on the lid. The 2N3055 is a common example of a TO-3 package and is often used in DC motor control.

File:TO-3, 2N3055 (unshaded).svg - Wikimedia Commons
T0-3 Type -2N3055

TO-18 / TO-39 Package Transistors

The TO-18/39 packages are another transistor package that was very widely used in the previous century but however has lost its popularity today. Unlike the TO-92, the TO-18 is a metal case that is hollow internally.

Since the case is circular a tab is connected to the bottom of the case to indicate pin 1 and the part number is printed on the side of the case. While not commonly used in transistors anymore, laser diodes in CD and DVD players are commonly housed in a TO-18 package with a lens attached to the top.

2N2222 NPN Bipolar Transistor TO-18 Metal Package buy online at Low Price in  India - ElectronicsComp.com
2N2222 NPN Bipolar Transistor Under the TO-18 / TO-39 Package Transistors

TO-126 Package Transistors

The TO-126 is a transistor package whose size is intermediate to that of TO-220and a TO-92.

Its size is smaller however its leg width is same as that on a T0-220.

The component part number is printed on the front while the back may be metalized for mounting to a heat sink. This package is now obsolete.

MJE200 NPN Power Transistor TO-126 Package buy online at Low Price in India  - ElectronicsComp.com
MJE200 NPN

Surface Mount Transistors

SMD transistor is now the integral part of the trasisitor industry due to its wide usage and availability in variety of forms.

SMD transistors have a direct proportionality with size and power handling capacity. One of the problems with SMD transistors is that very small parts may not have their part number printed on them, making identification very difficult.

BSP20 100mA 300V Surface Mount NPN High Voltage Transistor Philips
BSP20 100mA 300V Surface Mount NPN High Voltage Transistor Philips

SOT-23 Package Transistors

The SOT-23 package is the most compact in terms of size.It has three legs with one of the other side to ensure correct placing of the package.

SOT-23 packages may not have their part numbers printed as they are so small and if they do have something printed, it may be a portion of the code that only allows the designer to know what the part actually is. 

PNP NPN General Purpose Transistor Amplifier SOT-23 Package, ट्रांजिस्टर्स  - Electronics Store 4U, Kalyan | ID: 21281249362
SOT-23 Package Transistors

TO-263 / D2PAK

The D2PAK transistor case is very similar to the TO-220 package but differs in the fact that is surface mounted. These parts have their part number printed on the front face, a very small tab, and two legs at the front. They find applications DC motors where high power applications are in use.

D2PAK (TO-263) MOSFET Power Discrete - Amkor Technology
D2PAK (TO-263)

SOIC / SOP

Sometimes multiple transistors of identical characteristics are needed in a circuit (such as push/pull amplifiers). WSP4884 is used and has tow NMOS. Also NMOS andnPMOS maybr used together which is known as CMOS which has several applications and is also a highly efficient switch.

Small outline integrated circuit - Wikipedia

Conclusion

Transistors is the beginning to the world of electronics ,ad there’s a lot more to be learned. In summary, transistors are electronic devices that are commonly used to amplify or switch electrical signals. They are made up of three layers of a semiconductor material, and operate on the principle of a voltage or current being applied to the gate to control the flow of current between the source and the drain. Transistors are an essential component of modern electronics, and are used in a wide range of devices.

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