Diagram of using a multimeter to measure the polarity and quality of the positive and negative poles of a diode
By using a multimeter to measure resistance or conducting on-off tests, it is easy to determine the polarity of the positive and negative terminals of a diode and roughly measure its quality.
Diode positive and negative poles
Generally, diodes have a direct indication of the positive and negative poles. When you see the section of the shell with a white coil, it is the negative pole. Or the shorter side of the wire is the negative pole. But what if these features are not present?
A multimeter is a tool commonly used by electricians. When using the ohm range (resistance measurement) of a multimeter to measure the positive and negative resistance of a diode, it is important to note that the black probe of the terminal marked with a "-" on the multimeter case is connected due to the battery inside the multimeter; Connect the red probe of the terminal marked with a "+" on the watch case. The current flows out from the red probe and back from the black probe. In addition, the ohm range of Rx1000 should be used for measurement, because the current in Rx1 range is too high, and the voltage in Rx10K range is too high, which can easily damage the diode, so it is not suitable for use.
The specific testing method is shown in the figure on the right. Connect the two probes of the multimeter to the two pins of the diode. The forward resistance of a diode is very small, usually ranging from tens to hundreds of ohms, while the reverse resistance is very large, usually between tens to hundreds of kiloohms. If in the two tests in the figure, the right test shows a lower resistance and the left test shows a higher resistance, it can be concluded that the pin connected to the red probe on the right is the positive terminal of the diode, and the other pin is the negative terminal.
Some modern digital multimeters may have a gear (on/off) for judging the quality of the diode. Set the multimeter to this gear for measurement. If there is a reading, the red probe will be the positive terminal. If there is no reading or "1" is displayed, the black probe will be the positive terminal.
Judging the quality of diodes
Still using the resistance range measurement method of a multimeter as mentioned above to determine. If there is a significant difference in the measured forward and reverse resistance, it indicates that the unidirectional conductivity of the diode is good; If the resistance values measured twice are either very small or very large, it indicates that the diode has lost its unidirectional conductivity and there may be a faulty diode with quality issues.
