FFD-200 Perkin Elmer Optoelectronics, FFD-200 Datasheet - Page 18

• Manufacturer Part Number: FFD-200
• Description: si Pins Large Area
• Manufacturer: Perkin Elmer Optoelectronics

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photocells
www.optoelectronics.perkinelmer.com
Features
• Lowest-cost visible detector
• Available in low-cost plastic-
• Responsive to both very low light
• Wide dynamic range: resistance
• Low noise distortion
• Maximum operating voltages of 50
• Available in center-tap dual-cell
• Easy to use in DC or AC circuits
• Usable with almost any visible or
• Available in a wide range of
Typical Analog Applications
• Camera Exposure Control
• Auto-Focus for Slide Projector
• Colorimetric Test Equipment
• Densitometer
• Electronic Scales—dual-cell
• Automated Rear-View Mirror
Typical Digital Applications
• Automatic Headlight Dimmer
• Night Light Control
• Oil Burner Flame Out
• Street Light Control
• Absence/Presence (beam breaker)
• Position Sensor
Datasheets available upon request
encapsulated packages as well
as hermetic packages (TO-46,
TO-5, TO-8)
levels (moonlight) and to very high
light levels (direct sunlight)
changes of several orders of
magnitude between "light" and
"no light"
to 400 volts are suitable for opera-
tion on 120/240 VAC
configurations as well as specially
selected resistance ranges for
special applications
near-infrared light source such as
LEDS; neon; fluorescent, incandes-
cent bulbs, lasers; flame sources;
sunlight; etc.
resistance values
Description
Photocells or Light-Dependent Resistors can provide a very
economical and technically superior solution for many applications
where the presence or absence of light is sensed (digital operation)
or where the intensity of light needs to be measured (analog
operation).
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 applied
voltage. Silicon photodiodes are examples of this type of detector.
In contrast, bulk-effect photoconductors have no junction. The
bulk resistivity decreases with increasing illumination, allowing
more photocurrent to flow. This resistive characteristic gives
bulk-effect photoconductors a unique quality: signal current from
the detector can be varied over a wide range by adjusting the
applied voltage. To clearly make this distinction, PerkinElmer
Optoelectronics refers to its bulk-effect photoconductors as
photoconductive cells or, simply, photocells.
Photocells are thin-film devices made by depositing a layer
of a photoconductive material on a ceramic substrate. Metal
contacts are evaporated over the surface of the photoconductor and
external electrical connection is made to these contacts. These thin
films of photoconductive material have a high sheet resistance.
Therefore, the space between the two contacts is made narrow
and interdigitated for low cell resistance at moderate light levels.
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