What is a photosensitive diode?

Last Update Time: 2018-12-29 14:09:47

Photosensitive diode is one of the most commonly used photosensitive devices.

Compared with ordinary semiconductor diodes, it is similar that the tube core is a one-to-one PN junction with unidirectional conductivity, and the difference is that the light diode shell has a "window" that can shoot light.


l  Pinciple of photosensitive diode

When light is focused on the photodiode tube core by an organic glass lens ("window"), causing a change in the resistance of the PN junction of the tube and receiving the corresponding change. On the circuit, there will be a leakage current, and the leakage current is called photocurrent.

The reverse leakage current of PN junction is very small when no light is irradiated, and the leakage current is called the dark current.


l  The main parameters of the photosensitive diode

 (1) Maximum working voltage Vmax

Maximum working voltage is the value of the reverse voltage allowed on the photosensitive one pole in the case of no light irradiation and the reverse current does not exceed the specified value (0.1μA). It is usually within the range of 10~50V.


(2) Dark current ID dark current refers to the reverse leakage current when the light sensitive one is added to the normal working voltage in the absence of light, and the smaller the better, the better the value is, the general <0. 5 μA.


 (3) The photocurrent IL photocurrent means that the current of the photosensitive diode is about dozens of μA when a fixed light beam is irradiated with a normal reverse voltage.


l  Detect a photosensitive diode

(1) The identification of the feet

Dial the multimeter to the RX1kΩ block. First, a black paper is used to cover the transparent window of the photosensitive diode, and the two electrodes of the photosensitive diode are touched by the multimeter red and the black pen. If the multimeter pointer is turned to the right, the electrode is P pole (positive pole), and the electrode connected by the red surface pen is N pole (negative pole).

(2) judging from the foregoing, the forward resistance of the tube is smaller (10~ 20kΩ), and the reverse resistance is larger (infinity). If the positive and negative resistance values are very small or large, it means that the photodiodes have been broken or open inside, and the tubes are no longer in use. The multimeter is placed in the RX1kΩ block, the red surface pen connects to the P pole (positive pole), and removes the shaded black paper, so that the transparent window of the photosensitive diode is directed toward the light source (such as natural light, incandescent lamp or flashlight). The multimeter pointer should be deflected from the infinite position to the right, the greater the deflection angle, the higher the sensitivity of the light sensitive diode. If the tube is aligned with the light source, there is no wobble on the multimeter pointer.

It indicates that the light sensitive transistor has been damaged. When using the digital meter to measure, use the diode barrier to insert the corresponding electrode into the human table socket. In the presence of light and light, the indication voltage of the multimeter should be changed to be good and constant.

This article is from Allicdata Electronics Limited.