Digital multimeter for the detection of diode conduction voltage
In this position, the red test lead is connected to the positive power supply inside the multimeter, and the black test lead is connected to the negative power supply inside the multimeter. The connection between the two test leads and the diode is shown in Figure 1. If measured according to the connection method in Figure 1(a), the diode under test is forward conducting, and the multimeter displays the forward conducting voltage of the diode in mV. Generally, the forward voltage of a good silicon diode should be 500mV~800mV, and the forward voltage of a good germanium diode should be 200mV~300mV. If "000" is displayed, it means that the diode is broken down and short-circuited. If "1" is displayed, it means that the diode is blocked in the forward direction. If measured according to the connection method in Figure 1(b), "1" should be displayed, indicating that the diode is reversely blocked. If "000" or other values are displayed, it means that the diode has reverse breakdown. This file can also be used to judge the quality of the transistor and identify the pins. When measuring, first connect one test lead to a certain identified pin, and then connect the other test lead to the other two pins successively. If there is continuity or no continuity at all, then test the Change two test leads and test again. If there is no conduction or conduction both times, it can be determined that the transistor is good, and the identified pin is the base of the transistor. If the red test lead is connected to the base and the black test lead is connected to the other two poles and both are conductive, it means that the transistor is NPN type, otherwise, it is PNP type. Finally, compare the forward conduction voltages of the two PN junctions. The one with a larger reading is the be junction, and the one with a smaller reading is the bc junction. From this, both the collector and the emitter are identified.
