What is the diode and how to judge whether it is good or bad?

1. Diode introduction.

    A diode is a semiconductor component, represented by the letter D，PD，ZD. The diode has two poles, namely, P pole and N pole, P pole is also called positive pole, and N pole is also called negative pole.

The electrical property of the diode is one-way conduction, the current can only flow from the diode positive electrode, from the negative electrode. If the positive voltage of the diode is higher than the negative voltage, the diode is switched on and the internal resistance of the diode is very small. When the positive voltage of the diode is less than the negative voltage, the diode will stop, and the internal resistance of the diode is great or infinite. The conduction voltage drop of the diodes made of different materials is different. The forward conduction drop of silicon tube made of silicon material is 0.7V, and that of germanium tube made of germanium material is 0.3V. Most of the diodes used in the main board are silicon diodes.

In the circuit diagram, the symbols shown in fig. 1 are used to represent the diode, in which the left end is the diode P (positive pole) and the right end is the diode N pole (negative pole).

                          Fig.1 Diode symbol

2. Judgement of the diode is good or bad.

Use digital multimeter diode stopper, red meter pen contact diode positive pole, black meter pen contact diode negative pole, display value 300~800. Switch multimeter pen, red meter pen contact diode negative pole, black meter pen contact diode positive pole, display value is infinite. The measured results are consistent with those described above, indicating that the diode is good; if the numerical value is 0, the diode is short-circuited; both measurements are infinite, indicating that the diode is open circuit; and both measurements have values indicating the breakdown of the diode.

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