Semiconductor elements have played a huge role in shaping modern electronic systems. First bipolar transistor was invented in the first half of the 20th century. The bipolar transistor is made of three semiconductor layers with different types of conductivity (p-n-p or n-p-n), which results in two types of bipolar transistors - PNP and NPN. The individual layers have their names: E - emitter, B - base, C - collector. The basis of the use of the transistor is the dependence of the value of the greater current flowing between the emitter-collector junction, on the changes in the value of the lower current flowing in the base-emitter junction.

Phototransistors are optoelectronic elements. In terms of construction, phototransistors consist of three layers of semiconductors with successively changing types of conductivity (as the abovementioned scheme presents). Currently, phototransistors are not only a common component of many machines. These devices are also used in hobby programmable electronics and automation. Check below what products we have prepared for you - you will surely find something for yourself!

Phototransistors in theory and practice

Phototransistors are the next stage in the evolution of semiconductors. Using the photoelectric properties of semiconductors, a modified version of the transistors was invented - photo transistors. In phototransistors, the current value in the emitter-collector junction is not controlled by the base-emitter current. For this purpose, another parameter is used - the intensity of light incident on this junction.

Photons incident on the base-emitter junction polarize them in the direction of conduction. Thus, there is a continuous flow of current in the emitter-collector junction. Its value depends in turn on the value of the illuminance. In the off-light state, the transistor does not conduct current through the emitter-collector junction, which means it is simply off. Due to the fact that there is no need to supply the base-emitter junction with electric current, phototransistors usually have only two terminals: the emitter and the collector. However, it is worth to notice that there are also some phototransistors from which the base is derived and can be controlled like a regular bipolar transistor. The devices presented here have many advantages. The advantage of phototransistors over other photoelectric elements is a much shorter switching / response time and a much higher sensitivity.

Which phototransistor should I choose?

If you want to correctly select phototransistors for your projects, use the manufacturer's current-voltage characteristics. First of all, determine your need. To specify, indicate the preferred operating point of the phototransistor that will suit your needs and your project. An important parameter is the wavelength for which the phototransistor achieves the maximum sensitivity. In Botland you will find phototransistors with maximum sensitivities for wavelengths of 570 nm, 870 nm, 925 nm, 940 nm, which covers both visible and infrared radiation. When choosing such a device, carefully check all the parameters. You will find them by going to the product card of the selected device.

When I need to buy a phototransistor? The use of phototransistors

Phototransistors, due to their very high sensitivity and speed of operation, find a very wide range of applications. These are products that are used in radiation detection and wherever high system dynamics is required. Therefore, you will find them in measuring systems with high speed. Analog-to-digital converters in the systems are connected optoelectronic. What is more, you can use phototransistors as optoisolators to exchange signals between two electronic systems. There are many possibilities. It is noteworthy that the products offered in this category can be combined with other electronic components and build larger projects. Check also the product categories in which we present the Arduino and Raspberry Pi programmable electronics. See the Botland offer now and discover the possibilities of phototransistors and other measuring devices!