bipolar transistor

Also found in: Dictionary, Thesaurus, Medical, Acronyms.
Related to bipolar transistor: Field effect transistor, unipolar transistor

bipolar transistor

[bī′pō·lər tranz′is·tər]
A transistor that uses both positive and negative charge carriers.

bipolar transistor

A transistor made from a sandwich of n- and p-type semiconductor material: either npn or pnp. The middle section is known as the "base" and the other two as the "collector" and "emitter". When used as an amplifying element, the base to emitter junction is in a "forward-biased" (conducting) condition, and the base to collector junction is "reverse-biased" or non-conducting. Small changes in the base to emitter current (the input signal) cause either holes (for pnp devices) or free electrons (for npn) to enter the base from the emitter. The attracting voltage of the collector causes the majority of these charges to cross into and be collected by the collector, resulting in amplification.

Contrast field effect transistor.

bipolar transistor

Also called a "bipolar junction transistor" (BJT), it is one of two major transistor categories; the other is "field effect transistor" (FET). Although the first transistors and first silicon chips used bipolar transistors, most chips today are field effect transistors wired as CMOS logic, which consume less power (see FET and MOSFET).

Bipolar transistors are available as individually packaged discrete components as well as by the hundreds of thousands on a single chip.

High Power, High Frequency
Although the overall market for bipolar transistors has decreased, they are still used for high power applications and high radio frequency (RF) applications that reach into the gigahertz range. For example, from 1997 to 2002, worldwide sales of bipolar chips dropped from USD $1.5 billion to $226 million, the latter out of a total semiconductor market of $136 billion. See transistor, IGBT and BiCMOS.

The First Transistor Was Bipolar
In 1954, Texas Instruments pioneered the bipolar transistor. Although BJTs are fabricated in microscopic proportions on chips, individual discrete BJTs similar to this one are still in common use. (Image courtesy of Texas Instruments, Inc.)

NPN Bipolar Transistor
BJTs are either a sandwich of p-type silicon surrounded by n-type regions or n-type surrounded by p-type. To turn an NPN BJT on (example above), a negative potential is applied to the emitter terminal and a positive potential to the collector. When a positive voltage is applied to the base, it allows electrons to flow from the emitter to collector. For the PNP BJT, the polarities are reversed. The "bipolar" name comes from using both mobile carriers (electrons and holes).

Bipolars Use More Power
BJTs require continuous voltage at the base to keep the transistor closed (on) and current flowing from emitter to collector. In the field effect transistors (FETs) used in CMOS chips, the transistor is closed (turned on) by charging the gate, and current is only used during the gate charging period (see FET and MOSFET).

References in periodicals archive ?
Developers of bipolar transistors have long been aware that the current flows must generate some light, comments Russell D.
ST has been providing rad-hard bipolar transistors to the European aerospace industry for over 35 years and our products have accumulated hundreds of millions of flying hours," said Mario Aleo, Group VP and General Manager, Power Transistor Division, STMicroelectronics.
For analog applications, X-FAB offers bipolar transistors, several capacitor and resistor devices using the double-poly architecture, and precision analog devices with low temperature coefficients.
25 microwave bipolar complementary metal oxide semiconductor (BiCMOS) process offers high-performance technology with NpN heterojunction bipolar transistors (HBTs) up to fT/fmax= 180/220 GHz.
BiFET uniquely integrates indium gallium phosphide (InGaP)-based heterojunction bipolar transistors (HBTs) with field effect transistors (FETs) on the same GaAs substrate.
The devices feature latch-up immunity and a fast drive speed of 15 nF in 27 nS, which equip them with the ruggedness, high-power switching speeds and sharp edges needed to drive large MOSFETs and Insulated Gate Bipolar Transistors (IGBTs) in demanding, high-efficiency Switch Mode Power Supplies (SMPSs) and other high-speed, high-current switching applications.