BPW85B

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Optical Sensors - Phototransistors play an important role in various fields, due to the advantages they offer. Among all the optical sensors, BPW85B stands out for its advanced optical and electrical characteristics.

BPW85B are a kind of NPN silicon phototransistors, with GaAs infrared-emitting diodes (IREDs). BPW85B has an outstanding spectral response from 760nm to 1050nm, allowing it to detect a wide range of light wavelength. What’s more, it offers electrical and optical gains from 50 to 500, which is much larger than other conventional phototransistors. These features leave BPW85B outstandingly suitable for applications in different fields, such as sensing light source level, automatic control, smart home applications, and more.

In terms of BPW85B optical characteristics, it has a long wave peak-to-peak bandwidth, together with fast rise and fall times. Consequently, in contrast to conventional phototransistors, it allows for optical properties like a good wide dynamic range. The normal operating resistance on the collector is approximately 20 ohms and can be increased easily. Additionally, the transit time, the time it takes for a phototransistor to switch from switching off to switching on when illuminated by a light beam, is also extremely fast, at about 0.7 microseconds.

Moreover, BPW85B has an optimum response time to the incident light, or its speed in collecting light. BPW85B has a higher speed in collecting light than other phototransistors, responding to maximum brightness in about 1 microsecond. This property makes it suitable for applications in fields where high-speed measurements are needed.

In terms of the working principle, BPW85B is able to turn an input of light into an electrical current. Concretely speaking, when the photosensitive material absorbs a photon, an electron-hole pair is created. The electron holes move in opposite directions, widening the depletion region. As a result, a voltage is created, changing the potential of the collector layer, then turning the incident light into a current. The size of the voltage and current will depend on the amount of light received by the phototransistor.

Although BPW85B has great potential in various fields, it is not without its limitations. BPW85B is more easily affected by external noise than other phototransistors. Also, it works best when exposed to infrared light rather than visible light. Therefore, if the visible light is also needed to be measured simultaneously, a photodiode should be added as a supplement.

To sum up, BPW85B, as one of the most advanced phototransistors, is applicable in sensing light source level, automatic control, smart home applications, and more. By converting an input of light into a current, BPW85B provides great potential for application in these fields with its outstanding optical and electrical characteristics, such as spectral response, transit time, and optimum response time. Nevertheless, it is also affected by some limitations, such as noise and visible light measurement.

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