How to use an analog multimeter to determine the quality of a transistor
①Measure the NPN transistor: Set the ohm block of the multimeter at R × 100 or R × lk, connect the black test lead to the base, and connect the red test lead to the other two poles in succession. If the resistance values measured twice are larger than small, then connect the red test lead to the base, and connect the black test lead to the remaining two poles. If the resistance values measured twice are large, it means that the transistor is good.
②Measure the PNP transistor: Set the ohm block of the multimeter at R × 100 or R × lk, connect the red test lead to the base, and connect the black test lead to the other two poles in succession. If the resistance values measured twice are larger than small, then connect the black test lead to the base, and connect the red test lead to the remaining two poles. If the resistance values measured twice are large, it means that the transistor is good.
When the mark on the transistor is unclear, you can use a multimeter to initially determine the quality and type of the transistor (NPN type or PNP type), and identify the three electrodes e, b, and c. The test method is as follows:
① Use a pointer multimeter to determine the type of base b and triode: Set the ohm block of the multimeter at R × 100 or R × lk, first assume that a certain pole of the triode is the base, and connect the black test lead to the assumed base. Connect the red test lead to the remaining two poles one after another. If the resistance values measured twice are very small (or about a few hundred ohms to several thousand ohms), then the assumed base is correct and the transistor under test is NPN. type tube; same as above, if the resistance values measured twice are very large (about several thousand ohms to tens of kiloohms), then the assumed base is correct and the tested transistor is a PNP type tube. If the resistance values measured twice are one large and one small, then the originally assumed base is wrong. At this time, the other electrode must be re-assumed as the base and the above test must be repeated.
② Determine the collector c and emitter e: Still set the pointer multimeter ohm block at R × 100 or R × 1k. Taking the NPN tube as an example, connect the black test lead to the assumed collector c and the red test lead to the assumed On the emitter e, hold the b and c electrodes with your hands (b and c cannot be in direct contact), pass the human body, connect a bias resistor between b and C, read the resistance value shown on the meter, and then Reverse the connection of the two test leads and retest. If the resistance value measured for the first time is smaller than the second time, it means that the original hypothesis is established, because the small resistance value of c and e means that the current passing through the multimeter is large and the bias is normal. Today's analog multimeters have an interface for measuring the transistor amplification factor (Hfe). You can estimate the amplification factor of the triode.
