Tips for measuring transistor base with multimeter
The determination of transistor types and pin discrimination belongs to the electronic foundation. Generally, beginners in electrical technology will come into contact with the triple inversion and finding the base; PN junction, fixed tube type; Following the arrow, there is a large deviation; Uncertain, move your mouth. Perhaps it would be much easier, but of course, memorizing a mnemonic without knowing its meaning is useless.
The testing of the transistor is carried out using the ohm range R × 100 or R × 1k range of the multimeter. The pointer type multimeter has a red pen indicating the negative pole of the multimeter and a black pen indicating the positive pole of the multimeter battery. When testing a transistor type, the first step is to determine the base position of the pin. Measurement method: Randomly select two electrodes (such as electrodes 1 and 2), first measure the positive and negative resistance, and observe the deflection angle of the meter needle; Next, take electrodes 1 and 3 and
2. Measure the forward and reverse resistance of three electrodes by reversing them, and observe the deflection angle of the meter needle. In these three inverted measurements, there must be two measurement results that are similar: that is, in the inverted measurement, the pointer deviates greatly in one measurement and slightly in the other; The remaining measurement must be reversed, and the deflection angle of the pointer before and after the measurement is very small. The foot that was not measured this time is the base we are looking for
After the appeal measurement, we can determine the transistor type based on the PN junction direction between the base and the other two electrodes after determining the pin base. Measurement method: Place the black probe of the multimeter at the base and the red probe at any other electrode. If the pointer of the meter head deviates greatly, it indicates that the measured transistor is an NPN transistor; If the deflection angle of the meter pointer is very small, the tested tube is PNP type.
The third sentence of the mnemonic: Follow the arrow, deviate greatly
NPN transistor structure and current flow direction
NPN type transistor: According to the principle of the current flow through NPN type transistors, the positive and negative resistances Rce and Rec between the two poles are measured by reversing the black and red probes of a multimeter. Two measurement results are obtained, and it is found that the pointer deflection of the meter head is small. After careful observation, it will be found that there is one deflection angle that is slightly larger, that is, the current flow direction this time is: black pen → c pole → b pole → e pole → red pen, which matches the direction of the transistor symbol arrow. Therefore, at this time, the black probe must be connected to the collector c, and the red probe must be connected to the emitter e.
