Testing the Polarity and Condition of Ordinary Diodes Using a Multimeter
Detection principle: According to the unidirectional conductivity of diodes, diodes with good performance have low forward resistance and high reverse resistance; The greater the difference between these two values, the better. If they are similar, it indicates that the performance of the diode is poor or has been damaged.
When measuring, select the "ohm" range of the multimeter. Usually use Rx100 or Rxlk instead of Rx1 or Rx10k. Because the current in Rxl mode is too high, it is easy to burn out the diode, and the internal power supply voltage in Rxlok mode is too high, which is easy to break down the diode Measurement method: Connect two meter bars to the two electrodes of the diode and read the measured resistance value; Then swap the meter bars and measure again, taking note of the second resistance value. If there is a significant difference in resistance between the two times, it indicates that the diode has good performance; And based on the connection method of the meter rod with the lowest resistance measurement (referred to as forward connection), it is determined that the positive terminal of the diode is connected to the black meter rod and the negative terminal of the diode is connected to the red meter rod. Because the positive pole of the internal power supply of the multimeter is connected to the "-" socket of the multimeter, and the negative pole of the internal power supply is connected to the "+" socket of the multimeter.
If the resistance values measured twice are both very small, it indicates that the diode has broken down; If the resistance values measured twice are both very high, it indicates that the diode has already broken internally; if the resistance values measured twice are not significantly different, it indicates poor performance of the diode. In these cases, the diode cannot be used.
It must be pointed out that due to the nonlinear volt ampere characteristics of diodes, different resistance values will be obtained when measuring the resistance of diodes with different resistance levels of a multimeter; In actual use, the current flowing through the diode will be larger, so the resistance value presented by the diode will be smaller.
