What is a Photoconductive Cell?

Semiconductor light detectors can be divided into two major categories: junction and bulk effect devices. Junction devices, when operated in the photoconductive mode, utilize the reverse characteristic of a PN junction. Under reverse bias, the PN junction acts as a light controlled current source. Output is proportional to incident illumination and is relatively independent of implied voltage as shown in Figure 1. Silicon photodiodes are examples of this type detector.

APPLICATIONs
Photoconductive cells are used in many different types of circuits and applications.

Analog Applications
• Camera Exposure Control
• Auto Slide Focus - dual cell
• Photocopy Machines - density of toner
• Colorimetric Test Equipment
• Densitometer
• Electronic Scales - dual cell
• Automatic Gain Control - modulated light source
• Automated Rear View Mirror

Digital Applications
• Automatic Headlight Dimmer
• Night Light Control
• Oil Burner Flame Out
• Street Light Control
• Absence / Presence (beam breaker)
• Position Sensor