The method of measuring semiconductors with a digital multimeter
1, Diode
The open circuit voltage of the diode on the digital multimeter is about 2.8V, with the red probe connected to the positive and the black probe connected to the negative. When measuring, the current provided is about 1mA, and the displayed value is an approximate value of the forward voltage drop of the diode, measured in mV or V. The forward conduction voltage drop of a silicon diode is approximately 0.3-0.8V. The forward conduction voltage drop of germanium diode is about 0.1-0.3V. And diodes with higher power have a smaller forward voltage drop. If the measured value is less than 0.1V, it indicates that the diode is broken and both forward and reverse directions are conducting. If both the forward and reverse directions are open, it indicates that the PN section of the diode is open. For light-emitting diodes, when measuring in the forward direction, the diode emits light and the voltage drop of the tube is about 1.7V.
2, Transistor
The transistor has two PN sections, the emitter section (be) and the collector section (bc), which can be measured using the method of measuring diodes. In actual measurement, the forward and reverse voltage drop should be measured between every two pins, a total of 6 times. Among them, 4 times show an open circuit, and only 2 times show the voltage drop value. Otherwise, the transistor is faulty or a special transistor (such as a resistive transistor, Darlington transistor, etc., which can be distinguished from a conventional transistor by model). In two measurements with numerical values, if the black or red probe is connected to the same pole, then that pole is the base pole. The smaller measurement value is the collector node, and the larger measurement value is the emitter node. Because the base pole has been determined, the corresponding collector and emitter can be determined. At the same time, it can be determined that: if the black probe is connected to the same pole, the transistor is PNP type; if the red probe is connected to the same pole, the transistor is NPN type; Silicon tubes have a pressure drop of around 0.6V, while germanium tubes have a pressure drop of around 0.2V.
3, Thyristor:
The anode, cathode, and control electrode of the thyristor are open circuits, which can be used to determine the anode pins and determine whether the thyristor is broken down. The space between the thyristor control electrode and cathode is also a PN section, but there is a protective resistor between the high-power thyristor control electrode and cathode, and the displayed value during measurement is the voltage drop on the resistor.
4, Optocoupler
One side of the optocoupler is a light-emitting diode, with a voltage drop of about 1V during measurement. The other side is a transistor, some of which only leads out c and e, and the measurement is cut off in both forward and reverse directions. If all three pins are led out, the measurement characteristics are the same as those of the upper transistor (mostly NPN transistor). When using a multimeter to make the diode conduct in the forward direction, use another multimeter to measure the conduction voltage drop of transistor c to e, which is about 0.15V; Disconnect the multimeter connected to the diode, and the transistor c cuts off e, indicating that the optocoupler is good
