Method for measuring semiconductors with a digital multimeter
1、 Diode
The open circuit voltage of the digital multimeter diode is about 2.8V, with the red lead connected to the positive and the black lead connected to the negative. When measuring, the current provided is about 1mA, and the displayed value is the approximate value of the diode forward voltage drop, in mV or V. The positive conduction voltage drop of the 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 lower forward voltage drop. If the measured value is less than 0.1V, it indicates that the diode is broken down, and both the forward and reverse directions are conducting at this time. 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、 Triode
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 two times show the voltage drop value. Otherwise, the transistor is damaged or a special transistor (such as a bandgap transistor, Darlington transistor, etc., which can be distinguished from a common 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 the measured value is the collector node, and the larger is the emitter node. Since 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 thyristor anode, cathode, and control electrode are open circuits, which can be used to determine the anode pin and determine whether the thyristor is broken down. There is also a PN section between the thyristor control electrode and the cathode, but there is a protective resistor between the high-power thyristor control electrode and the 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 lead 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 the 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
