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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If yo still don’t understand you can ask again, but then I expect phototransistoe your question is specific about one part of the schematic. The circuit you show should work as it is, since it is already for a phototransistor. Please tell me if this is correct.

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. This is amplified by the current gain of the transistor in the normal way.

Power Transistors RF Transistor. Both versions of the phototransistor symbol are acceptable and understood. R1 will limit that.

Little Door Guard – Engineering Projects

What resources have you read vedor app notes, etc. Transistor Q1 will want to increase that fold to get mA collector current.

Eventually a point is reached where the phototransistor becomes saturated and the level of current cannot increase. Home Questions Tags Users Unanswered. As a result of their ease of use and their applications, phototransistors are used in many applications. In any case he has plenty of info about both versions now: The circuit symbol also has the convention arrow and directions on the emitter connection.

It actually works very well, off in normal light and starts turning on as soon as I start dimming the lights. Common collector phototransistor circuit Phototransistor circuit operation The phototransistor circuits can be used on one of two basic modes of operation. Like more conventional transistors, the phototransistor can be used in common emitter and common collector circuits. The switch mode, therefore has two levels: We are a franchised distributor of electronic components, as well as a sourcing and procurement agent for hard-to-find, obsolete, and allocated parts.


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.

With most circuits not using the base connection even if it is availablethe only way to change the mode of operation of the circuit is to change the value of the load resistor.

In fact a phototransistor can be made by exposing the semiconductor of an ordinary transistor to light. There is a small amount of current that flows in the photo transistor even when no light is present. Position sensing – in this application the optoisolator can be used to detect the position of a moving element, often the moving element has a light or interrupts a beam of light which the phototransistor detects.

Any schematic or circuit diagram would be really helpful. You may have to try a few different values of resistor in your circuit to arrive at your desired setting.

You can leave the base floating unconnected or connect it to ground through a resistor. This junction is designed to be relatively large to enable it to pick up sufficient quantities of light.

The basic concepts for the phototransisgor circuits are quite straightforward. Although ordinary transistors exhibit the photosensitive effects if they are exposed to light, the structure of the phototransistor is specifically optimised for photo applications. The light enters the base region where it causes hole electron pairs to be generated.

Photo transistors are operated in their active regime, although the base connection is generally left open circuit or disconnected because it is phototrsnsistor not required. These devices were generally made using diffusion or ion implantation. Like more conventional transistors, the phototransistor can be used in common emitter and common collector circuits.


Homojunction planar phototransistor structure Early photo transistors used germanium or silicon throughout the device giving a homo-junction structure.

The operation of the phototransistor circuit in the switch mode is more widely used in view of the non-linear response of the phototransistor to light. The current generated by the light affects the base region. 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.

Hetero-junction devices have a much higher limit and some can be operated at frequencies as high as 1 Photoransistor. The photo transistor has much larger base and collector areas than would be used for a normal transistor. 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.

Phototransistor circuits are normally relatively straightforward, especially of the detector is only required to detect the presence of absence of a particular light source. Early photo transistors used germanium or silicon throughout the device giving a homo-junction structure. This makes phototransistors more suitable in a number of applications.

What is a Phototransistor: tutorial & primer

What do I do? Phototransistor characteristics As already mentioned the photo transistor has a high level of gain 2j5777 from the transistor action. A beam of light is interrupted each time a coin or other item passes a given point. Try a higher value, around 10k and see if that makes a difference, if it’s still on when it’s light then increase further. The reason the circuit is usually not the best way to do this is because it relies upon Hfe, which can vary quite widely in a transistor 2n5777 is subject to temperature changes.

They are called active or linear mode and a switch mode.