Common transistor applications include digital and analog switches, signal amplifiers, power regulators and equipment controllers. Transistors are also the building blocks of integrated circuits and most modern electronics. Microprocessors often include more than a billion of them in each chip. Transistors are used in almost everything, from stoves to computers and pacemakers to aircraft.
The first transistors were produced in the late 1940s as semiconductor replacements for vacuum tubes. Early transistor applications included telephone equipment, radios and hearing aids. Room-sized computers were re-designed to use transistors, reducing their size and over-heating problems. Compared to tubes, transistors are small, cheap and lightweight—they're also durable and insensitive to vibration or shock. With no warm-up time, a low operating voltage and a long life span, the transistor quickly replaced most tube technology.
Increasing portability led to many new transistor applications in the 1950s and 1960s. Calculators, televisions and megaphones became smaller and more affordable; some of these were not even possible until the transistor was invented. Home stereos and amateur radio transmitters also became more accessible. The military used the transistor's high-power radio frequency (RF) abilities in radar and hand-held two-way radios. As the technology improved, some computer makers offered all-transistor models that no longer filled a whole room.
In the early 1960s, the integrated circuit (IC) was created, combining hundreds of interconnected transistors on a small chip. Soon, ICs held thousands of low-power transistors, making computers and consumer electronics very portable. Many discrete transistor applications remain for medium- and high-power devices, however. The material size and heat dissipation needed for greater current and voltage simply require a larger device. Most audio amplifiers, switching power supplies and motor controllers use individual power transistors, for example.
Many more power transistor applications exist, including vehicle ignitions, control systems and accessories. Medical devices, industrial machine controls and navigational equipment all rely on transistor characteristics. Power inverters for running household air-conditioning devices from direct current (DC) car batteries utilize high-current transistors. Some applications may also include digital, analog or mixed-signal ICs along with power transistors. Even medium-power circuits like coil and display drivers often use discrete transistors or a small transistor array.
Special-purpose transistor applications also utilize individual devices. Mobile phones and microwave systems include transistors capable of frequencies up to hundreds of Gigahertz. Radiation-hardened transistors are usually used in satellites and other aerospace applications. Extremely sensitive Darlington transistor pairs are often found in touch- and light-sensing devices. As part of an optoisolator, a phototransistor can also electrically isolate one circuit from another while still controlling it.