Photodiode
The photodiode is similar to the common semiconductor diode, but it has a feature that makes it very special: The photodiode is a device that converts light into current.
Incident Light (red arrows)
Direction of the generated current (blue arrow)
This current flows on the opposite direction of the arrow of the diode and is called leakage current.
The photodiode can be used as a light detector device, because it converts light into electricity. Any variation on the light causes a variation on the electricity. This variation is used to report that there was a change in the level of illumination on the photodiode.
The photodiode can be forward biased (the current flows on the direction of the arrow of the diode). In this case, the light on the photodiode has no effect and the photodiode behaves as a common diode
Most of photodiodes come equipped with a lens. This lens focuses the incident light so the reaction to light exposure is clearer.
The photodiode unlike the LDR or photoresistor, responds to the changes from darkness to light much quicker and vice versa, and it can be used with circuits with shorter response time.
When we place a photodiode between the collector and the base of the bipolar transistor (with the cathode of the diode pointing to the collector of the transistor), we have the equivalent circuit of the phototransistor.
A very important parameter of the photodiode is the responsivity. The responsivity is the radio of the generated current to the incident light
It looks similar to a Light-Emitting Diode (LED)
Related Links
- Phototransistor
- Photoresistor - LDR
- Continuous or direct current
- Alternating current (AC)
- 7-segment Display
- Optocoupler
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