Principles of Photodiode and Phototransistor

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* a type of photodetector capable of converting light into either current or voltage, depending upon the mode of operation. The common traditional solar cell used to generate electric solar power is a large area photodiode. * a semiconductor with a p-n junction

* Photons is the source of its energy
* Energy can be solved by the equation:
h =Planck’s constant= 6.624×10-34
f = frequency
* The frequency is, in turn, directly related to the wavelength (distance between successive peaks) of the traveling wave by the following equation: = Vf
= wavelength
f = frequency
V = velocity of light

* 1 lm=1.496×10-10 W
* Light intensity is measured in lmft2, footcandle (fc), or Wm2 * The operation of the photodiode is limited to reverse bias region. * The application of light will result to the transfer of energy(photons) * Dark current - current that will exist without illumination. APPLICATIONS

* employed in an alarm system.
* reverse will continue to flow as long as the light beam does not broken * used to count items in the conveyor’s belt.
* item passed the light beam then it will be broken the current will drops to the dark current level and the counter will increase.


* A photoelectric device with photosensitive collector-base p-n junction. The current induced by photoelectric effects is the base current of the transistor.


* If we assign the notation I , for the photoinduced base current, the resulting collector current, on an approximate basis is
Ic≅hfe I
* An increase in light corresponds with the increase in collector current. APPLICATIONS

* Punch-card readers
* Computer logic circuitry
* Lighting control
* Level indication
* Relays
* Counting systems
* High isolation AND gate using three phototransistors and three LED as is aid. *...
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