FET Fundamentals Unit 8 – Transducers
Exercise 2 – Photoconductive Cell Operation
EXERCISE OBJECTIVE
When you have completed this exercise, you will be able to demonstrate the effects of light on
the resistance of a photoconductive cell by using a test circuit. You will verify your results with a
multimeter.
EXERCISE DISCUSSION
- A photoconductive cell is made of photosensitive semiconductor material whose resistance
changes with light intensity. - Photoresistor is another name for a photoconductive cell.
- In the absence of light the resistance of the cell is very high. When the cell is exposed to
light, its resistance decreases. - The sensitivity of a photoconductive cell is the change in cell resistance when there is a
change in cell illumination. - Photoconductive cells are usually made of a layer of photoconductive semiconductor
material, such as cadmium sulfide (CdS) or cadmium selenide (CdSe), on a ceramic
substrate. The cell does not have a PN junction. - When used as part of a voltage divider, photoconductive cells provide a voltage output which
is directly or inversely related to light intensity. - Applications of photoconductive cells include light control and measurement, alarm and
relay controls, photometers and photographic exposure control.