Photo Transistors

Photo transistors are a device which converts light energy into electric energy. They are similar to photo resistors but they produce both current and voltage. They are made of bipolar semiconductors, which focus energy that passes through it. Photons activate the photo transistors and the light in the exposed base is amplified causing relatively high currents to pass through. This spreads from the base to the emitter where the current is concentrated and converted into voltage. Photo transistors are inexpensive, simple and several can fit on a microchip but they are vulnerable to surges and electromagnetic interference. There are several types of photo transistors. The photo bipolar transistor is housed in a transparent case. Field-effect photo transistors (also known as photoFETs) are light sensitive and can control drain-source current. They respond to visible radiation range and infrared. P_N_P and N_P_N are different configurations; they can be common emitters, common collectors or common base. Photo transistors are commonly used in astronomy, night vision equipment and laser-range finding. They are basic components of security systems like smoke detectors, encoders, relays, CD players and punch-card readers. Automatic light controls on public roads are activated by photo transistors and so are virtually all light-activated electronic devices.

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