Use a multimeter to measure the polarity of the positive and negative poles of the diode and whether it is good or bad
With the help of a multimeter to measure the resistance or the on-off test gear, you can easily find out the polarity of the positive and negative poles of the diode and roughly measure the quality of the diode.
Diode positive and negative
Generally, the diodes directly indicate the positive and negative poles. When you see the section of the white coil on the tube shell, it is the negative pole. Or the shorter side of the wire is the negative pole. But what if you don't have these characteristics?
The multimeter is a tool that electricians have in their hands. When using the ohm range (measurement resistance) of the multimeter to measure the positive and negative resistance of the diode, since the multimeter is connected to a battery, it is necessary to pay attention to the connection of the terminal marked "-" on the multimeter case. The black test leads are connected; the red test leads of the terminals marked with "+" on the case are connected. The current flows out from the red test lead and flows back from the black test lead. In addition, the ohm range of Rx1000 should be used for measurement, because the current of Rx1 file is too large, and the voltage of Rx10K file is too high, which is easy to damage the diode, so it is not suitable to use.
The specific test method is shown in the figure on the right. Connect the two test leads of the multimeter to the two pins of the diode respectively. The forward resistance of the diode is very small, generally tens of ohms to hundreds of ohms, while the reverse resistance is very large, generally tens of kilohms to hundreds of kilohms. 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 test pen 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 gear for judging whether the diode is good or bad (on-off gear). Set the multimeter at this gear for measurement. If there is a reading, the red test pen is positive. If there is no reading or "1" is displayed, it is black. The test lead is positive.
Diode good or bad judgment
It is still judged by the above measurement method using the resistance file of the multimeter. If there is a large difference between the measured forward and reverse resistances, it means that the unidirectional conductivity of the diode is good; Bad diodes with quality issues.
