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Related to phototransistor: Optocoupler


A junction transistor that may have only collector and emitter leads or also a base lead, with the base exposed to light through a tiny lens in the housing; collector current increases with light intensity, as a result of amplification of base current by the transistor structure.



a transistor, usually bipolar, in which minority carriers are injected on the basis of an internal photoelectric effect. Phototransistors are used to convert light signals into amplified electric signals.

A phototransistor consists of a single-crystal Ge or Si semiconductor wafer in which three regions are produced by means of special technological processes. As in a conventional transistor, the regions are called the emitter, collector, and base; as a rule, the base has no lead. The crystal is placed in a housing with a transparent window. A phototransistor is connected to an external circuit in the same way as a bipolar transistor with a common-emitter connection and a zero base current. When light is incident on the base or collector, charge-carrier pairs (electrons and holes) are generated in that region; the carrier pairs are separated by the electric field in the collector junction. As a result, the carriers accumulate in the base region, causing a reduction of the potential barrier in the emitter junction and an increase, or amplification, of the current across the phototransistor in comparison with the current that is due only to the migration of carriers generated directly by the action of the light.

As with other photoelectric devices, such as photocells and photodiodes, the main parameters and characteristics of photo-transistors are the luminous sensitivity, spectral response, and time constant. The luminous sensitivity is the ratio of the photoelectric current to the incident luminous flux. For the best specimens of phototransistors—for example, diffused planar devices—the luminous sensitivity may be as high as 10 amperes per lumen. The spectral response, which is the sensitivity to monochromatic radiation as a function of wavelength, defines the long-wavelength limit for the use of a particular phototransistor; this limit, which depends primarily on the width of the forbidden band of the semiconductor material, is 1.7 micrometers for germanium and 1.1 micrometers for silicon. The time constant characterizes the inertia of a phototransistor and does not exceed several hundred microseconds. In addition, a phototransistor is characterized by the photoelectric gain, which may be as high as 102–103.

The high reliability, sensitivity, and temporal stability of phototransistors, as well as their small size and relatively simple design, have led to their extensive use in control and automation systems, for example, as light detectors and as components of optoisolators (seeRADIATION DETECTOR, OPTICAL DETECTOR, and OPTRON). Field-effect phototransistors, which are similar to field-effect transistors, were developed in the 1970’s.


Ambroziak, A. Konstruktsiia i tekhnologiia poluprovodnikovykh fotoelektricheskikh priborov. Moscow, 1970. (Translated from Polish.)



A transistor that uses light rather than electricity to cause an electrical current to flow from one side to the other. It is used in a variety of sensors that detect the presence of light. Phototransistors combine a photodiode and transistor together to generate more output current than a photodiode by itself. See photoelectric, photodiode and transistor.
References in periodicals archive ?
Ma explained that the newly designed phototransistor displays high sensitivity and stable performance while also having a high level of flexibility.
The Thingumajig is the perfect gadget to figure out why a thingy out, point it at the Thingumajig's phototransistor.
The oscilloscope and the golf ball timing system were used to measure the time interval between the ball blocking the light to the first phototransistor (just inside the half-tube) and the ball blocking a phototransistor 15.
One important aspect of the success of the new phototransistors is the researchers' innovative "flip-transfer" fabrication method, in which their final step is to invert the finished phototransistor onto a plastic substrate.
A phototransistor output on-state collector current of 0.
A key condition for the linear mode is that the phototransistor is not in saturation.
Available with a single phototransistor that activates a momentary "on" position, rugged pushbuttons are snap-in mounted for easy installation.
Koppens at ICFO, have demonstrated a QD/2-D(graphene) phototransistor with a photoresponse up to 5 orders of magnitude higher than phototransistors based on single graphene or MoS2 atomic layers without QDs, showing the potential of QD/2-D hybrid devices for photovoltaics.
Electrical performance of the output phototransistor is characterized at collectoremitter voltages of 24 and 30 V and power dissipation of 100 mW.
Each phototransistor has a wide 60 [degrees] acceptance angle and is available in four sensitivity ranges with minimum and maximum values for tighter design control.
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Powder or Varnish CANNOT be used on the ballot as they will interfere with the scanning of the ballot by the phototransistor.