Skip to main content

bipolar transistor

bipolar transistor A semiconductor device having three electrodes: emitter, base, and collector. It is effectively a sandwich of two types of doped semiconductor, usually p-type and n-type silicon, and so contains two p-n junctions. When the region common to both junctions is p-type, an npn transistor is formed; when it is n-type a pnp transistor is formed. This central region forms the base electrode.

Bipolar transistors are so named because both charge carriers, i.e. electrons and holes, contribute to the flow of current. Current flow between collector and emitter is established by applying a forward bias between base and emitter. In linear (i.e. nonsaturated) operation, the magnitude of this current is proportional to the input current drawn at the base. The current flow is in opposite directions in npn and pnp transistors.

If the base current is increased but the collector current is restrained, so that the transistor effectively receives more base current than it would seem to require, the transistor is driven into a state of saturation, also known as bottoming. It then behaves as a very efficient switch since the base-collector junction becomes reverse-biased and, in saturation, the collector-emitter voltage can fall as low as 20 millivolts. The device thus seems virtually a short circuit. Bipolar transistor switches, working into saturation, are the basis of TTL circuits. Saturated transistors do however have a fairly low switching speed. The much higher switching speeds of Schottky TTL and ECL circuits are achieved by using a nonsaturated mode of operation.

Cite this article
Pick a style below, and copy the text for your bibliography.

  • MLA
  • Chicago
  • APA

"bipolar transistor." A Dictionary of Computing. . Encyclopedia.com. 16 Dec. 2018 <https://www.encyclopedia.com>.

"bipolar transistor." A Dictionary of Computing. . Encyclopedia.com. (December 16, 2018). https://www.encyclopedia.com/computing/dictionaries-thesauruses-pictures-and-press-releases/bipolar-transistor

"bipolar transistor." A Dictionary of Computing. . Retrieved December 16, 2018 from Encyclopedia.com: https://www.encyclopedia.com/computing/dictionaries-thesauruses-pictures-and-press-releases/bipolar-transistor

Learn more about citation styles

Citation styles

Encyclopedia.com gives you the ability to cite reference entries and articles according to common styles from the Modern Language Association (MLA), The Chicago Manual of Style, and the American Psychological Association (APA).

Within the “Cite this article” tool, pick a style to see how all available information looks when formatted according to that style. Then, copy and paste the text into your bibliography or works cited list.

Because each style has its own formatting nuances that evolve over time and not all information is available for every reference entry or article, Encyclopedia.com cannot guarantee each citation it generates. Therefore, it’s best to use Encyclopedia.com citations as a starting point before checking the style against your school or publication’s requirements and the most-recent information available at these sites:

Modern Language Association

http://www.mla.org/style

The Chicago Manual of Style

http://www.chicagomanualofstyle.org/tools_citationguide.html

American Psychological Association

http://apastyle.apa.org/

Notes:
  • Most online reference entries and articles do not have page numbers. Therefore, that information is unavailable for most Encyclopedia.com content. However, the date of retrieval is often important. Refer to each style’s convention regarding the best way to format page numbers and retrieval dates.
  • In addition to the MLA, Chicago, and APA styles, your school, university, publication, or institution may have its own requirements for citations. Therefore, be sure to refer to those guidelines when editing your bibliography or works cited list.