• Phototransistor is a light sensitive transistor.
• In one common type of phototransistor, the base lead of a BJT is replaced by a light sensitive surface.
• When the light sensitive surface @ the base is kept in darkness, the collector-emitter pair of the BJT does not conduct.
• When the light sensitive surface @ the base is exposed to light, a small amount of current flows from the base to the emitter. The small base-emitter current controls the larger collector-emitter current.
• Alternatively, one can also use a field-effect phototransistor (Photo FET).
• In a photo FET, the light exposure generates a gate voltage which controls a
drain-source current.
• In one common type of phototransistor, the base lead of a BJT is replaced by a light sensitive surface.
• When the light sensitive surface @ the base is kept in darkness, the collector-emitter pair of the BJT does not conduct.
• When the light sensitive surface @ the base is exposed to light, a small amount of current flows from the base to the emitter. The small base-emitter current controls the larger collector-emitter current.
• Alternatively, one can also use a field-effect phototransistor (Photo FET).
• In a photo FET, the light exposure generates a gate voltage which controls a
drain-source current.
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