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All bipolar transistors are light sensitive: photons striking the semiconductor create electron-hole pairs which make the transistor conduct.
In ordinary transistors this is an undesirable source of noise, so they are packaged in opaque metal or plastic cases.
A phototransistor on the other hand is packaged either in a metal case with a transparent lens or in transparent plastic to let light in.
Note: this is not a significant effect with MOS transistors.
Wiki User
∙ 6y ago
Wiki User
∙ 11y agoThey are semiconductor devices. See attached link for how they work.
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What are the characteristics phototransistor 2N5777?
http://pdf1.alldatasheet.com/datasheet-pdf/view/86407/ASI/2N5777.html * High Sensitivity * Economical T0-92 Compatible Package ~MECHASUN~
What is a phototransistor?
There is a wide selection of photosensitive devices that are available to the electronic designer. Whilst photo-diodes fulfil many requirements, phototransistors or photo transistors are also available, and are more suitable in some applications. Providing high levels of gain, and standard devices are low cost, these phototransistors can be used in many applications.The idea of the photo transistor has been known for many years. William Shockley first proposed the idea in 1951, not long after the ordinary transistor had been discovered. It was then only two years before the photo transistor was demonstrated. Since then phototransistors have been used in a variety of applications, and their development has continued ever since.Phototransistor structureAlthough ordinary transistors exhibit the photosensitive effects if they are exposed to light, the structure of the phototransistor is specifically optimised for photo applications. The photo transistor has much larger base and collector areas than would be used for a normal transistor. These devices were generally made using diffusion or ion implantation. Homojunction planar phototransistor structureEarly photo transistors used germanium or silicon throughout the device giving a homo-junction structure. The more modern phototransistors use type III-V materials such as gallium arsenide and the like. Heterostructures that use different materials either side of the p-n junction are also popular because they provide a high conversion efficiency. These are generally fabricated using epitaxial growth of materials that have matching lattice structures. These photo transistors generally use a mesa structure. Sometimes a Schottky (metal semiconductor) junction can be used for the collector within a phototransistor, although this practice is less common these days because other structures offer better levels of performance.Heterojunction mesa-structure phototransistorIn order to ensure the optimum conversion and hence sensitivity, the emitter contact is often offset within the phototransistor structure. This ensures that the maximum amount of light reaches the active region within the phototransistor.Phototransistor operationPhoto transistors are operated in their active regime, although the base connection is left open circuit or disconnected because it is not required. The base of the photo transistor would only be used to bias the transistor so that additional collector current was flowing and this would mask any current flowing as a result of the photo-action. For operation the bias conditions are quite simple. The collector of an n-p-n transistor is made positive with respect to the emitter or negative for a p-n-p transistor. The light enters the base region of the phototransistor where it causes hole electron pairs to be generated. This mainly occurs in the reverse biased base-collector junction. The hole-electron pairs move under the influence of the electric field and provide the base current, causing electrons to be injected into the emitter.Phototransistor characteristicsAs already mentioned the photo transistor has a high level of gain resulting from the transistor action. For homo-structures, i.e. ones using the same material throughout the device, this may be of the order of about 50 up to a few hundred. However for the hetero-structure devices, the levels of gain may rise to ten thousand. Despite their high level of gain the hetero-structure devices are not widely used because they are considerably more costly to manufacture. A further advantage of all phototransistors when compared to the avalanche photodiode, another device that offers gain, is that the phototransistor has a much lower level of noise. One of the main disadvantages of the phototransistor is the fact that it does not have a particularly good high frequency response. This arises from the large capacitance associated with the base-collector junction. This junction is designed to be relatively large to enable it to pick up sufficient quantities of light. For a typical homo-structure device the bandwidth may be limited to about 250 kHz. Hetero-junction devices have a much higher limit and some can be operated at frequencies as high as 1 GHz.The characteristics of the photo-transistor under different light intensities. They are very similar to the characteristics of a conventional bipolar transistor, but with the different levels of base current replaced by the different levels of light intensity.There is a small amount of current that flows in the photo transistor even when no light is present. This is called the dark current, and represents the small number of carriers that are injected into the emitter. Like the photo-generated carriers this is also subject to the amplification by the transistor action.
What does work transfer?
Work is the transfer of force
Can an Industrial Engineer work as a Electrical Engineer?
No, There's difference b/w that work. If they no how to work then they can do!
What is the definition of work input?
Work input is the information and tools used to create the final product. Raw material is considered work input for products.
Is a npn phototransistor normally open or normally closed?
It depends on the phototransistor's design. Most are normally open until you shine light on them.
What are the 3 legs of a phototransistor?
Emitter, base & collector.
What are the characteristics phototransistor 2N5777?
http://pdf1.alldatasheet.com/datasheet-pdf/view/86407/ASI/2N5777.html * High Sensitivity * Economical T0-92 Compatible Package ~MECHASUN~
What is photo interrupter module?
A photo interrupter module for a smoke alarm has a gallium-arsenide infrared LED and silicon phototransistor that is contained in a plastic housing. When smoke interrupts the slot between the receiver and sender, the module is switched on.
How does a laser-ranging device work?
The laser light is pulsed and shone onto a reflective surface. The returned reflection is picked up by a phototransistor. The time taken for the pulse to be sent and returned, can be measured by electronics within the device. The speed of light is 300,000 Km /sec, (186,000 miles/sec) which is very fast, but finite. The timing circuits within the device have to be very accurate and stable. This is acheived by using crystal oscillators within the device, to act as timing comparison.
How does a laser-ranging device work's?
The laser light is pulsed and shone onto a reflective surface. The returned reflection is picked up by a phototransistor. The time taken for the pulse to be sent and returned, can be measured by electronics within the device. The speed of light is 300,000 Km /sec, (186,000 miles/sec) which is very fast, but finite. The timing circuits within the device have to be very accurate and stable. This is acheived by using crystal oscillators within the device, to act as timing comparison.
What is an example of something that uses a semiconductor?
diodes, rectifierstransistors (unijunction, bipolar junction, field effect)silicon controlled rectifierssolar cellsphotosensors (cadmium sulfide, photodiode, phototransistor)light sources (light emitting diode, LASER diode)integrated circuits (analog, digital, hybrid, charge coupled device camera image sensor, etc.)imaging drum in a xerographic photocopier or LASER printeretc.
Can be a phototransistor be used for saving electric energy?
A photo transistor is a gate which is sensitive to light. Therefore it can be used in any circumstances where a circuit needs to be sensitive to light. Circuits which employ photo transistors and their relatives the photo-resistor and photo-diodes, are already used in such equipment as light switching. These circuits determine if it is dark enough to turn on street and domestic lights and turn them on or off when a preset level of light is present.
How do you determine the collector and emitter terminals of a phototransistor?
Answer: First you have to find the Base, with your millimeter set to diodes play around with the probes between the three pins until you get a reading between one pin to both the other two pins that pin will be your Base, if your red probe is on that pin then it is a NPN transistor, if it is the black probe then it is a PNP, there will be a slight difference in the reading, the pin with the smallest reading will be the Collector and the larger is the Emitter
What are the disadvantages of phototransistor?
Phototransistors have several important advantages that separate them from other optical sensors. For example, phototransistors produce a higher current than photodiodes while also being able to produce a voltage, something that photoresistors cannot do. Phototransistors are very fast and are capable of providing nearly instantaneous output. Phototransistors are relatively inexpensive, simple, and small enough to fit several of them onto a single integrated computer chip.
What is a phototransistor?
There is a wide selection of photosensitive devices that are available to the electronic designer. Whilst photo-diodes fulfil many requirements, phototransistors or photo transistors are also available, and are more suitable in some applications. Providing high levels of gain, and standard devices are low cost, these phototransistors can be used in many applications.The idea of the photo transistor has been known for many years. William Shockley first proposed the idea in 1951, not long after the ordinary transistor had been discovered. It was then only two years before the photo transistor was demonstrated. Since then phototransistors have been used in a variety of applications, and their development has continued ever since.Phototransistor structureAlthough ordinary transistors exhibit the photosensitive effects if they are exposed to light, the structure of the phototransistor is specifically optimised for photo applications. The photo transistor has much larger base and collector areas than would be used for a normal transistor. These devices were generally made using diffusion or ion implantation. Homojunction planar phototransistor structureEarly photo transistors used germanium or silicon throughout the device giving a homo-junction structure. The more modern phototransistors use type III-V materials such as gallium arsenide and the like. Heterostructures that use different materials either side of the p-n junction are also popular because they provide a high conversion efficiency. These are generally fabricated using epitaxial growth of materials that have matching lattice structures. These photo transistors generally use a mesa structure. Sometimes a Schottky (metal semiconductor) junction can be used for the collector within a phototransistor, although this practice is less common these days because other structures offer better levels of performance.Heterojunction mesa-structure phototransistorIn order to ensure the optimum conversion and hence sensitivity, the emitter contact is often offset within the phototransistor structure. This ensures that the maximum amount of light reaches the active region within the phototransistor.Phototransistor operationPhoto transistors are operated in their active regime, although the base connection is left open circuit or disconnected because it is not required. The base of the photo transistor would only be used to bias the transistor so that additional collector current was flowing and this would mask any current flowing as a result of the photo-action. For operation the bias conditions are quite simple. The collector of an n-p-n transistor is made positive with respect to the emitter or negative for a p-n-p transistor. The light enters the base region of the phototransistor where it causes hole electron pairs to be generated. This mainly occurs in the reverse biased base-collector junction. The hole-electron pairs move under the influence of the electric field and provide the base current, causing electrons to be injected into the emitter.Phototransistor characteristicsAs already mentioned the photo transistor has a high level of gain resulting from the transistor action. For homo-structures, i.e. ones using the same material throughout the device, this may be of the order of about 50 up to a few hundred. However for the hetero-structure devices, the levels of gain may rise to ten thousand. Despite their high level of gain the hetero-structure devices are not widely used because they are considerably more costly to manufacture. A further advantage of all phototransistors when compared to the avalanche photodiode, another device that offers gain, is that the phototransistor has a much lower level of noise. One of the main disadvantages of the phototransistor is the fact that it does not have a particularly good high frequency response. This arises from the large capacitance associated with the base-collector junction. This junction is designed to be relatively large to enable it to pick up sufficient quantities of light. For a typical homo-structure device the bandwidth may be limited to about 250 kHz. Hetero-junction devices have a much higher limit and some can be operated at frequencies as high as 1 GHz.The characteristics of the photo-transistor under different light intensities. They are very similar to the characteristics of a conventional bipolar transistor, but with the different levels of base current replaced by the different levels of light intensity.There is a small amount of current that flows in the photo transistor even when no light is present. This is called the dark current, and represents the small number of carriers that are injected into the emitter. Like the photo-generated carriers this is also subject to the amplification by the transistor action.
What are DVDs made of?
Materials In DVD'sCD's, DVD's are usually made from a thin piece of optically clear plastic with a layer on top of some type of silvered metal, with additives to cause it to discolor when exposed to laser light.
