Typical Applications for
Phototransistors and IREDs


Why Use Phototransistors?

Phototransistors are solid state light detectors that possess internal gain. This makes them much more sensitive than photodiodes of comparably sized area. These devices can be used to provide either an analog or digital output signal. This family of detectors offers the following general characteristics and features:

Why Use IREDs?

IRED's are solid state light sources which emit light in the near-IR part of the spectrum. Because they emit at wavelengths which provide a close match to the peak spectral response of silicon photodetectors both GaAs and GaAlAs LEDs are often used with phototransistors and photodarlingtons. Key characteristics and features of these light sources include:

Applications

Phototransistors can be used as ambient light detectors. When used with a controllable light source, typically and LED, they are often employed as the detector element for optoisolators and transmissive or reflective optical switches. Typical configurations include:

Optoisolator
The optoisolator is similar to a transformer in that the output is electrically isolated from the input.
Optical Switch
An object is detected when it enters the gap of the optical switch and blocks the light path between the emitter and detector.
Retro Sensor
The retrosensor detects the presence of an object by generating light and then looking for its reflectance off of the object to be sensed.
Phototransistors and IREDs have been used in the following applications.
Computer/Business Equipment
  • track zero detector - floppy drive
  • margin controls - printers
  • read finger position - touch screen
  • detect holes - computer card
  • monitor paper position - copiers

Industrial

  • LED light source - light pens
  • security systems
  • safety shields
  • encoders - measure speed and direction
  • photoelectric controls
Consumer
  • coin counters
  • position sensors - joysticks
  • remote controllers - toys, appliances, audio/visual equipment
  • games - laser tag

Medical

  • provide electrical isolation between patient and equipment
  • monitor intravenous injection rates
Fundamental Circuit Approaches

Basic Circuits

More Output Current Capability
More Voltage Switching Capability

Reducing Dark Current


For a copy of the original data sheet, or to send comments, E-Mail us at: eod@egginc.com
Or call us at 1-800-775-OPTO (6786).

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