Modes of Operation
Two basic modes of operation, active mode and switch mode, are used in phototransistor circuits.
• Switch mode is more commonly used. It describes a non-linear response to light; when there is no light no current flows into the transistor. Current begins to flow as exposure to light increases. Switch mode operates in an on/off system.
• Active mode, also known as linear mode, responds in a way that is proportional to the light stimulus.