Phototransistors
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Description
Phototransistors are photodiode-amplifier combinations
integrated within a single silicon chip. These are combined to
overcome the major fault of photodiodes: unity gain. Many
applications demand a greater output signal from the photodetector
than can be generated by a photodiode alone. While the signal
from a photodiode can always be amplified through use of an
external op-amp or other circuitry, this approach is often not as
practical or as cost-effective as the use of phototransistors. The
phototransistor can be viewed as a photodiode whose output
photocurrent is fed into the base of a conventional small-signal
transistor. While not required for operation of the device as a
photodetector, a base connection is often provided, allowing the
designer the option of using base current to bias the transistor. The
typical gain of a phototransistor can range from 100 to over 1500.
Phototransistors can be used as ambient-light detectors. When
used with a controllable light source, typically an IRED, they
are often employed as the detector element for optoisolators and
transmissive or reflective optical switches.
All phototransistors are RoHS compliant.
Features
• Low-cost visible and near-IR
photodetection
• Available with gains from 100
to over 1500
• Moderately fast response times
• Available in a wide range of
packages including epoxy-coated,
transfer-molded, cast, hermetic
packages, chip form and surface
mounting technology
• Usable with almost any visible
or near-infrared light source such
as IREDs, neon, fluorescent,
incandescent bulbs, lasers, flame
sources, sunlight, etc.
• Same general electrical
characteristics as familiar signal
transistors
Typical Applications
• Computer/business equipment
• Write-protect control
• Margin controls—printers
• Industrial
• LED light source—light pens
• Security systems
• Safety shields
• Consumer
• Coin counters
• Lottery card readers
• Position sensors—joysticks
• Remote controllers—toys,
appliances, audio/visual
equipment
• Games—laser tag
• Camera shutter control
Principle of Operation
Phototransistors are solid-state light
detectors that possess internal gain.
They can be used to provide either
an analog or digital output signal.
Datasheets available upon request.
Absolute Maximum Ratings
Maximum Temperatures -25°C to 80°C (CR10TE, CR50TE)
Storage and Operating: -40°C to 100°C
-40°C to 110°C (VTT1015, VTT1016,
VTT1017, VTT1115, VTT1116, and VTT1117)
-40°C to 85°C (VTT7222, VTT7223,
VTT7225, VTT7122, VTT7123, and VTT7125)
-40°C to 70°C (VTT9002, VTT9003,
VTT9102, and VTT9103)
Continuous Power Dissipation: 50 mW
100 mW (VTT9002, VTT9003, VTT9102,
and VTT9103)
200 mW (CR10TE, CR50TE)
250 mW (VTT1015, VTT1016, VTT1017,
VTT1115, VTT1116, and VTT1117)
Derate above 30°C: 0.71 mW/˚C
2.5 mW/˚C (VTT9002, VTT9003, VTT9102,
and VTT9103)
3.12 mW/˚C (VTT1015, VTT1016, VTT1017,
VTT1115, VTT1116, and VTT1117)
0.91 mW/˚C (VTT7122, VTT7123, VTT7125)
Maximum Current: 25 mA
200 mA (VTT1015, VTT1016, VTT1017,
VTT1115, VTT1116, and VTT1117)
Lead-Soldering Temperature: 260°C (1.6 mm from case, 5 sec. max.)
phototransistors