Digital Multimeter: Diode Forward Voltage Test
In this gear, the red probe is connected to the positive power supply inside the multimeter, and the black probe is connected to the negative power supply inside the multimeter.
The connection between the two probes and the diode is shown in Figure 1.
If measured according to the connection in Figure 1 (a), the tested diode is conducting in the forward direction, and the multimeter displays the forward conduction voltage of the diode in mV.
Typically, a good silicon diode should have a forward conduction voltage of 500mV to 800mV, and a good germanium diode should have a forward conduction voltage of 200mV to 300mV.
If "000" is displayed, it indicates that the diode is short circuited due to breakdown. If "1" is displayed, it indicates that the diode is not forward. If measured according to the connection in Figure 1 (b), it should display "1", indicating that the diode is reverse cut off.
If it displays "000" or other values, it indicates 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 probe to a designated pin, and then connect the other probe to the other two pins in sequence. If both probes are conducting or not conducting twice, then switch the two probes and measure again.
If both probes are not conducting or conducting twice, it can be determined that the transistor is good, and it can be determined that the designated pin is the base of the transistor.
If the red probe is connected to the base and the black probe is connected to the other two poles, both conducting, it indicates that the transistor is of NPN type.
Otherwise, it is of PNP type. *After comparing the magnitude of the forward conduction voltage between two PN junctions, the one with the larger reading is the be junction, and the one with the smaller reading is the bc junction, thus both the collector and emitter are identified.
