How to measure NPN transistor with pointer multimeter?

Multimeters include digital multimeters and analog multimeters. Both types of meters can measure. Let me show you the measurement methods one by one.

1. Digital multimeter measurement

When using a digital multimeter to measure, use the "diode mode" for measurement. The red test lead is equivalent to the positive pole of the battery, and the black test lead is equivalent to the negative pole of the battery.

Transistors are divided into NPN type and PNP type tubes, and their internal structures are different. However, there is a PN junction between the B pole and the C and E poles. When the test lead applies forward voltage to the PN junction, it can be turned on.

When measuring with a digital multimeter, current flows from the red test lead.

▲ NPN type, B pole is connected to the red test lead, black test lead is connected to C and E, it will be conductive

If it is an NPN type transistor, when the B pole is connected to the red test lead and the C and E poles are connected to the black test lead, the PN junction will conduct forward and the multimeter will display the conduction voltage. The conduction voltage of the PN junction of a transistor made of silicon material is generally about 0.7V.

▲ PNP type, B pole is connected to the black test lead, and the red test lead will be connected to C and E.

If it is a PNP type transistor, when the B pole is connected to the black test lead, and the C and E poles are connected to the red test lead, the PN junction will conduct forward, and the multimeter will display the conduction voltage.

When measuring, we can first assume that one of the poles is the B pole, and then use one of the test leads to fix it on the assumed B pole, and the other test lead to contact the remaining two pins respectively.

If there is no continuity during the two measurements, you can interchange the test leads and measure until you find the B pole.

If the conduction voltage displayed during measurement is 0V, it means that the transistor has an internal breakdown and has been damaged.

After finding the B pole, you can find the C pole and the E pole. Hold the B pole and the assumed C pole with your hands, and then put the test leads to the assumed C pole and the assumed E pole. If there is no continuity, Red and black test leads are interchangeable.

If there is still no continuity after exchanging the test leads, change another electrode, assuming it is the C electrode, and then place the test leads on the assumed C electrode and the assumed E electrode to measure.

2. Measurement with pointer multimeter

When using a pointer multimeter to measure, the resistance range "Rx10K range" is used for measurement. If the resistance range is used for measurement in other ranges, the pointer may deflect too small to be easily observed.

When using the resistance setting of the analog multimeter, the red test lead is equivalent to the negative pole of the battery, and the black test lead is equivalent to the positive pole of the battery. That is, the current flows out from the black test lead, which is different from the digital multimeter.

When measuring, we can first assume that one of the poles is the B pole, and then use one of the test leads to fix it on the assumed B pole, and the other test lead to contact the remaining two pins respectively.

If there is no continuity during the two measurements, you can interchange the test leads and measure until you find the B pole.

After finding the B pole, you can find the C pole and the E pole. Hold the B pole and the assumed C pole with your hands, and then put the test leads on the assumed C pole and the assumed E pole, and observe the deflection of the pointer. , exchange the red and black test leads and test again.

Then change another electrode and assume it is the C pole, and then put the test lead on the assumed C pole and the assumed E pole to measure. Observe the deflection of the pointer, exchange the red and black test leads and measure again.

When judging the C pole and the E pole, you need to measure 4 times. At the time when the pointer deflects the most, the pole that is not pinched by your hand is the E pole.