Characteristics of diodes and multimeter testing methods

The English word for diode is diode. The positive and negative terminals of a diode are (as shown in Figure 1). The positive terminal A is called the anode and the negative terminal B is called the cathode. Current can only move from the anode to the cathode.

2. How to use a multimeter to measure the positive and negative poles of a diode

When performing a simple test on the semiconductor diode, the ohm range of the multimeter should be used. The measurement method is shown in (Figure 2, Figure 3). The red test lead connected to the + input of the multimeter is connected to the negative pole of the power supply in the meter ; while the black test lead connected to the - input of the multimeter is connected to the positive pole of the power supply in the meter .

The measurement method is to first set the multimeter to the "Ohm" position (usually R×100 or R×1K), and then use the multimeter to connect the two poles of the diode. When the power supply in the meter makes the diode in the forward connection, the diode is turned on and the resistance is small (in the range of tens of ohms to thousands of ohms), which tells us that the black test lead is in contact with the positive pole of the diode; the red test lead is in contact with the negative pole of the diode (see Figure 3); when the power supply in the meter makes the diode in the reverse connection, the diode is cut off and the resistance is very large (usually hundreds of kiloohms), which tells us that the black test lead is in contact with the negative pole of the diode and the red test lead is in contact with the positive pole of the diode.

3. Why are the forward resistance values ​​of the same diode different when measured with a multimeter at R×100 and R×1K?

When measuring the forward resistance of the same diode using the R×100 and R×1K ranges of the multimeter, the measured resistance values ​​are different. This is because the equivalent internal resistance r corresponding to the two ranges of R×100 and R×1K is different, and when the power supply voltage E remains unchanged, the current flowing through the meter is also different.