Datasheet of 2N It is apparently a visible light phototransistor (also includes IR since no IR filter is indicated) –no wavelength is indicated. PHOTOTRANSISTOR. Part Number: WP3DP3BT. Features. ○ Mechanically and spectrally matched to the infrared emitting. LED lamp. ○ Blue transparent lens. The circuit you show should work as it is, since it is already for a phototransistor. Just leave your base lead floating. EDIT – the breadboard.

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In fact a phototransistor can be made by exposing the semiconductor of an ordinary transistor to light. This means the base resistor must be chosen according to the particular transistor used. The collector is taken to the supply voltage via a collector load resistor, and the output is taken from the collector connection on the phototransistor. The common emitter phototransistor circuit configuration is possibly the most widely used, like its more conventional straight transistor circuit.

The choice of common emitter or common collector phototransistor circuit configuration phototranisstor upon the requirements for the circuit. However the circuits are normally reliable and can easily be designed. This arises from the large capacitance associated with the base-collector junction.

It is perfectly possible to have a PNP phototransistor, and for this the direction of the arrow on the emitter is reversed in the normal way.

Phototransistor Symbol and Circuit Configurations

Rc or Re in the diagrams above. 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.

Whatever your manufacturing need, come to 1-Source to buy electric components from the leading electronic 2n577 distributors and electronic component suppliers! Terms of Sale Terms of Use. Access to the base connection allows the phototransistor circuit conditions to be set phototramsistor appropriately for some applications.

In this case the base will be shown in the normal way on the phototransistor symbol. If you don’t understand it right away, read it a second time, and try to imagine the current flows. Can you please show a picture or something, I am a newbie and can’t really understand your explaination. Common base circuits are not normally used because the base phototrransistor is often left floating internally and may not be available. This generation mainly occurs in the reverse biased base-collector junction.


Phototransistor Circuit Configurations | Applications | Electronics Notes

Old OC71 transistor – by removing the black paint it exhibited phototransistor characteristics One of the drawbacks of the phototransistor is that is particularly slow and its high frequency response is very poor Phototransistor circuit symbol The phototransistor symbol consists of the basic transistor symbol with two arrows pointing towards the junction of the transistor.

Now if Q2 the phototransistor gets light it will also draw current, and draw it away from Q1. All other aspects of the circuit function remain the same. The performance of the phototransistor can be superior to that of the photodiode for some applications in view of its gain. The basic concepts for the phototransistor circuits are quite straightforward. The phototransistor can be used in a variety of different circuit configurations.

Broadcast technology Embedded Design principles Distribution Formulae. 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. 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. On some phototransistors, the base connection is available.

Common base circuits are not normally used because the base connection is often left floating. First move the LED to the transistor’s collector, and add a series resistor.

You may have to try a few different values of resistor in your circuit to arrive at your desired setting. It was then only two years before the photo transistor was demonstrated.

High values of base resistor R b prevent low levels of light from raising the current levels in the collector emitter circuit and in this way ensuring a more reliable digital output. Eventually a point is reached where the phototransistor becomes saturated and the level of current cannot increase.


The common collector, or emitter follower phototransistor circuit configuration has effectively the same topology as the normal common emitter transistor circuit – the emitter is taken to ground via a load resistor, and the output for the circuit being taken from the emitter connection of the device. As already mentioned the photo transistor has a high level of gain resulting from the transistor action.

There is a small amount of current that flows in the photo transistor even when no light is present. Both versions of the phototransistor symbol are acceptable and understood. As a result of their ease of use and their applications, phototransistors are used in many applications. Sorry Stevenvh never mind.

Heterostructures that use different materials either side of the p-n junction are also popular because they provide a high conversion efficiency. So if you are intending to eventually power this circuit from something else other than a coin cell, then you should go for the common emitter circuit Steven describes.

The site you got the phototransistir circuit from also has an example of such a circuit: Phototransistor circuit symbol NPN It is perfectly possible to have a PNP phototransistor, and for this the direction of the arrow on the emitter is reversed in the normal way.

The site you got the above circuit from also has an example of such a circuit:. The circuit actually acts as an amplifier. In addition, we provide excess inventory consignment, electronic engineering and product design services, prototyping, contract manufacturing, handheld portable computing products, and software application development services. They are called active or linear mode and a switch mode.

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What is a Phototransistor: tutorial & primer

Hetero-junction devices have a much higher limit phototranzistor some can be operated at frequencies as high as 1 GHz. The characteristics of the photo-transistor under different light intensities.

You do need a resistor, and with the LED on the collector’s side your series resistor will limit the current.