How to measure semiconductors with a digital multimeter
1. Diodes
The open circuit voltage of the diode gear of the digital multimeter is about 2.8V, the red test lead is connected to the positive, and the black test lead is connected to the negative. When measuring, the current is about 1mA, and the displayed value is the approximate value of the forward voltage drop of the diode, and the unit is mV or V. The forward voltage drop of a silicon diode is about 0.3~0.8V. The forward conduction voltage drop of germanium diode germanium is about 0.1~0.3V. And the forward voltage drop of the diode with higher power is smaller. If the measured value is less than 0.1V, it means that the diode is broken down, and both forward and reverse conduct. If both forward and reverse are open, it means that the PN junction of the diode is open. For light-emitting diodes, the diode emits light when measured in the forward direction, and the tube voltage drop is about 1.7V.
2. Transistor
The triode has two PN sections, the emission section (be) and the collector section (bc), which can be measured according to the method of measuring the diode. In the actual measurement, the forward and reverse voltage drop should be measured between every two pins, a total of 6 times, of which 4 times showed open circuit, and only 2 times showed the voltage drop value, otherwise the triode is bad or a special triode (Such as band-stop triodes, Darlington triodes, etc., can be distinguished from ordinary triodes by model). In two measurements with values, if the black test lead or the red test lead is connected to the same pole, then this pole is the base, the smaller measured value is the collector node, and the larger one is the emitter node, because the base has been judged, Correspondence can determine the collector and emitter. At the same time, it can be judged: if the black test leads are connected to the same pole, the triode is PNP type; if the red test leads are connected to the same pole, the triode is NPN type; the silicon tube with a voltage drop of about 0.6V is a silicon tube, and the one with a voltage drop of about 0.2V is a germanium tube. Tube.
Three, thyristor:
The anode, cathode and control electrode of the thyristor are open-circuited, based on which the anode pin can be determined and whether the thyristor breaks down can be judged. There is also a PN junction between the control electrode and the cathode of the thyristor, but there is a protection resistor between the control electrode and the cathode of the high-power thyristor, and the displayed value is the voltage drop on the resistance during measurement.
4. Optocoupler
One side of the optocoupler is a light-emitting diode, the voltage drop is about 1V when measuring, and the other side is a triode, some only lead out c and e, and the positive and negative directions of the measurement are cut off. If all three pins are led out, the measurement characteristics are the same as the above triode (mostly NPN tube). When a multimeter is used to make the diode conduct forward, at this time, another multimeter is used to measure the conduction voltage drop of the triode c to e, which is about 0.15V; disconnect the multimeter connected to the diode, and the triode c to e is cut off, indicating that the optocoupler is good
