Photodiode and photodiode determine positive and negative

Direct plug: The pins of photodiodes can usually be distinguished by directly checking the length of the pins of photodiodes: the long pin is the positive pole (P pole), and the short pin is the negative pole (N pole). Light-emitting diodes: Light-emitting diodes are very simple, that is, the long pin is positive and the short pin is negative, and a current limiting resistor must be connected.

Direct-insertion photodiode pin polarity identification method:

The long pin is connected to the cathode of the diode inside the phototube. However, since the photodiode is different from the ordinary diode and is used in reverse, the long pin will be connected to the positive pole of the power supply, so the long pin is determined as the positive pole.

A photodiode uses its dark current to measure the light intensity of the current environment and is generally used in reverse connection.

Patch: The one with a green bar at the bottom is the negative pole

For tubes with colored dots or tube key marks, the leg close to the mark is the positive pole and the other leg is the negative pole. 　　

Photodiode positive and negative detection

When there is no light, the volt-ampere characteristic of the photodiode is the same as that of an ordinary diode. The reverse current at this time is called dark current, which is generally between a few microamperes and hundreds of microamperes. Its value increases with the increase of reverse bias voltage and the increase of ambient temperature. When detecting weak photoelectric signals, it is necessary to consider using tubes with small dark current. Generally, photodiodes work in two states: adding reverse voltage or not adding voltage. When there is light, the reverse current of the photodiode will increase linearly with the increase of light intensity (within the range of 10-103Lux) within a certain reverse bias voltage range (UR≥5V). The reverse current at this time is also called photocurrent. Therefore, corresponding to a certain light intensity, the photodiode is equivalent to a constant current source. When there is light but no external voltage, the photodiode is equivalent to a photocell, the output voltage P area is positive, and the N area is negative. As the light intensity changes, the output voltage of the two poles of the photodiode also changes due to photoelectric conversion. Therefore, you can use a digital multimeter to distinguish the positive and negative poles. The method is to set the multimeter to the Rx1k position, block the light-receiving window of the tube with an object, and measure two resistance values ​​by swapping the red and black test leads. The larger resistance value is measured (reverse resistance). The pin connected to the red test lead is the negative pole, and the pin connected to the black test lead is the positive pole.