Measure the polarity and quality of the positive and negative poles of a diode using a multimeter
By using a multimeter to measure resistance or the on/off test gear, it is easy to find the polarity of the positive and negative poles of the diode and roughly measure the quality of the diode.
Diode positive and negative poles
Generally, diodes have a section that directly represents the positive and negative poles. When you see the section with a white coil on the casing, 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 (measuring resistance) 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 "-" on the multimeter case is connected to the battery inside the multimeter; The red probe of the terminal marked with "+" on the case is connected. The current flows out from the red probe and back from the black probe. In addition, the Rx1000 ohm range should be used for measurement, as the current in the Rx1 range is too high and the voltage in the Rx10K range is too high, which can easily damage the diode, so it is not suitable to use it.
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 ranging from tens to hundreds of kiloohms. If in the two tests in the figure, the test on the right shows a small resistance and the test on the left shows a large resistance, it can be concluded that the pin connected to the red probe on the right is the positive pole of the diode, and the other pin is the negative pole.
Some modern digital multimeters may have a range for judging the quality of the diode (on/off range). Set the multimeter at this range for measurement. If there is a reading, the red probe will be positive. If there is no reading or a display of "1", the black probe will be positive.
Diode quality judgment
The measurement method using a multimeter resistance range is still used to determine. If the measured forward and reverse resistances differ significantly, it indicates that the unidirectional conductivity of the diode is good; If the resistance values measured twice are both small or large, it indicates that the diode has lost its unidirectional conductivity, and there is a faulty diode with quality issues.
