The output is created by connecting a resistor between the emitter pin of the com- ponent and ground. 2) generates an output which transitions from a low state to a high state when IR light is detected by the phototransistor. How- ever, the component has an internal amplifier (in this case a phototransistor) which magnifies this current to useful levels. It is called an amplifier circuit because the current generated in the component when light is detected is very small. The output voltage is read at the terminal of the collector. The output is created by connecting a resistor between the voltage supply and the collector pin of the component. The wavelength range for light in the near- infrared region is about 700 nanometers (nm) to 1100 nm. 1) generates an output which transitions from a high state to a low state when light in the near-infrared range is detected by the phototransistor. The common-emitter amplifier circuit (Fig. These devices converts detected light into current for the circuit to use. Almost all electronic devices like smoke detectors and optical remote controls that rely on light employs phototransistors in their system. Phototransistors are solid-state devices that serves as light detectors with internal gain and used to provide analog or digital signals. It discusses its operation and how things work inside these devices. This applications note presents some basic facts about phototransistors including its different architectures commonly used in the industry.

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