Page 24 - Shellie Suzana Binti Saad

EXERCISE 3

With the aid of a circuit diagram,

explain the operation of the

phototransistor.

The phototransistor circuits can be
applied in two basic modes of
operation. They are called active or

linear mode and switch mode.

Switch mode means the

phototransistor will either be off or
on for a digital logic response to the
object sensed.

Active mode means the
phototransistor generates an output

response based on the light or
irradiance level.

The collector current will be proportional to the coupled
light intensity. The actual operation of a phototransistor
depends on the biasing arrangement and light frequency.

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