Digital multimeter for measuring semiconductors
I. Diode
Digital multimeter diode file open-circuit voltage of about 2.8V, the red pen is connected to the positive, the black pen is connected to the negative, the measurement of the current provided by about 1mA, the display value of the diode forward voltage drop approximation in mV or V. Silicon diode forward conduction voltage drop of about 0.3 ~ 0.8V. germanium diode germanium forward conduction voltage drop of about 0.1 ~ 0.3V. and the greater the power of the diode forward voltage drop to be a little smaller. If the measured value is less than 0.1V, the forward voltage drop will be smaller. If the measured value is less than 0.1V, it means that the diode breaks down, at this time both forward and reverse conduction. If the forward and reverse are open, it means that the diode PN section is open. For light-emitting diodes, forward measurement of diode light, tube voltage drop of about 1.7V.
Second, triode
Triode has two PN section, emitter section (be) and collector section (bc), according to the measurement of the diode can be measured. In the actual measurement, each of the two pins should be measured between the forward and reverse voltage drop, a total of 6 times, of which 4 times show open circuit, only two times to show the value of the voltage drop, otherwise the triode is bad or a special triode (such as band resistance triode, Darlington triode, etc., can be distinguished by the model number and the ordinary triode). In two measurements with values, if the black or red pen is connected to the same pole, the pole is the base pole, the smaller measurement value is the collector section, the larger is the emitter section, because the base pole has been judged, corresponding to the collector and emitter can be judged. At the same time can be judged: if the black pen to the same pole, the transistor is PNP type, if the red pen to the same pole, the transistor is NPN type; pressure drop of 0.6V or so is the silicon tube, pressure drop of 0.2V or so is the germanium tube.
Third, silicon controlled:
SCR anode and cathode and control pole is open circuit, according to which you can determine the anode pin and determine whether the SCR breakdown. Thyristor control pole and cathode is also between the PN section, but high-power thyristor control pole and cathode between a protective resistor, the measurement shows the value of the resistor on the voltage drop.
Fourth, the photocoupler
Optocoupler side of the light-emitting diode, measuring the voltage drop of about 1V or so, the other side of the transistor, some only cited c, e, measurement of forward and reverse are cut off, if the three feet are cited, the measurement of the characteristics of the same as the above transistor (more for the NPN tube). When a multimeter to make the diode forward conduction, this time with another multimeter to measure the transistor c to e conduction voltage drop of about 0.15V; disconnect the diode connected to the multimeter, the transistor c to e cut-off, indicating that the optocoupler is good!
