Electronic Light Detectors - Phototransistors

A phototransistor is a special case of a photodiode with internal gain. The device comprises a bipolar transistor in a transparent (or windowed) package that allows light to reach the base-collector junction. Photons strike the base-collector junction, generating electrons that are injected into the base; this photodiode current is amplified by the gain of the transistor. Although phototransistors do have a higher responsivity for light than other photodiodes, they are no better at detecting low levels of light. Phototransistors also have significantly longer response times than standard photodiodes. However, they do exhibit high levels of reliability, sensitivity and temporal stability, together with small size. These factors have led to their extensive use as light detectors in control and automation systems, and also as component parts of optoisolators. Click below for product data sheets