bipolar transistor

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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 ?
On electrodes of a drain field two-gate of the transistor VT2 and the collector of the bipolar transistor VT3 exists a complete resistance, an active component of which has a negative value, and on reactive--capacity character.
Substituting the expressions for real and imaginary parts of the Z parameters from Equation 5 into Equation 4, the optimum values of imaginary parts of the feedback elements [Mathematical Expression Omitted], [Mathematical Expression Omitted] and [Mathematical Expression Omitted] expressed through the parameters of the bipolar transistor equivalent circuit are given by
A particular issue with the use of bipolar transistors in high voltage circuits is avoiding simultaneous high voltages and high currents that may lead to secondary breakdown failure.
Therefore, a GaAs HBT essentially is a super-charged bipolar transistor.
The industry s first bipolar transistors in low-profile LFPAK56(Power SO-8) SMD power plastic package from NXP Semiconductors deliver thermal and electrical performance comparable to larger bipolar transistors, and is suited for applications in power management, load switch, linear mode voltage regulator, backlighting and automotive.
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.
While MOSFETs have become the default choice of power switch for many power management designers, bipolar transistors have continued to develop away from the media spotlight and in some applications can prove to be the better choice of power switch.
16 and 32 W Linear Power GaAs FETs Challenge Silicon Bipolar Transistors in L-Band
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Listing the wide voltage range of Zetex bipolar transistors, MOSFETs and diodes, the discrete component section also provides data for the new 'Miniature Package Power Solutions, a series of bipolar transistors and MOSFETs housed in ultra compact micro-lead packages (MLP).
We have developed an array of mixed-signal technologies, such as our Bipolar-CMOS-DMOS (BCD) portfolio of processes, which allows the use of bipolar transistors for precision analog, advanced CMOS technology for digital functions, and DMOS for monolithic power transistors.