- Photodarlington transistor basics
- SDP8105 Silicon Photodarlington
- See also
Photo Darlington is a phototransistor that is related to Darling transistor family also called Darlington phototransistor or photodarlington.
The photodarlington transistor provides a much higher degree of sensitivity when compared to other phototransistors, but this is at the expense of response time and frequency response.
In the photodarlington transistor configuration, the first transistor acts as the photodetector, and its emitter is coupled into the base of the second transistor. This gives a very much higher level of gain, but it is very much slower than the ordinary phototransistor, having a maximum frequency of around 20 kHz.
SDP8105 Silicon Photodarlington
The photodarlington symbol is a combination of the standard phototransistor symbol and the Darlington transistor symbol.
Photo Darlingtons are only used where low frequencies are required. The combination of the lower frequency response of the phototransistor as opposed to the photodiode and the darlington configuration as opposed to a single transistor means that the photodarlington typically has a low frequency response. Some may only have a bandwidth of a few tens of kHz. It also has a much higher ON voltage between the collector and emitter than a single transistor.
- T-1 plastic package
- 20¡ (nominal) acceptance angle
- Consistent optical properties
- Mechanically and spectrally matched to SEP8505 and SEP8705 infrared emitting diodes
OUTLINE DIMENSIONS in inches (mm)
Tolerance 3 plc decimals ±0.005(0.12)
2 plc decimals ±0.020(0.51)
The SDP8105 is an NPN silicon photodarlington transfer molded in a T-1 black plastic package to minimize effect of visible ambient light. Transfer molding of this device assures superior optical centerline performance compared to other molding processes. Lead lengths are staggered to provide a simple method of polarity identification.
- Courtesy of Steven Engineering, Inc.
Revision date 13/9/2018