The basic function of the SMD transistor is to amplify, it can amplify the weak electrical signal to a certain intensity, of course, this conversion still follows the law of energy conservation, it just converts the energy of the power supply energy converted into a signal.

　　The formula for identifying the pins of the SMD transistors of the professional manufacturer of SMD secondary and tertiary tubes:

　　1. Three upside down, find the base

　　As we all know, SMT is a semiconductor device containing two PN junctions.

　　According to the different connection methods of the two PN junctions, they can be divided into two types of chip transistors with different conductivity types: NPN type and PNP type.

　　To test the SMD triode, please use the ohm gear of the multimeter and select the R×100 or R×1K gear. For an analog multimeter, the red lead is connected to the negative of the battery in the meter, and the black lead is connected to the positive of the battery in the meter.

　　Suppose we don't know whether the SMD transistor tested by the professional manufacturer of SMD diodes or tertiary diodes is NPN type or PNP type, and we don't know what electrode each pin is. One step of the test is to determine which pin is the base.

　　At this point, we take any two electrodes, invert the two test leads of the multimeter, measure their forward and reverse resistances, and observe the deflection angle of the test leads; then, invert electrodes 1, 3 and 2, 3 to measure their Forward and reverse resistance, observe the deflection angle of the needle.

　　In the three reverse measurements, there must be two similar measurement results: that is, in the reverse measurement, one deflection of the watch hand is large, and one deflection is small; the remaining time must be reversed. The deflection angle of the pointer before and after the measurement is very small.

　　　2. PN junction, fixed tube type

　　After finding the base of the chip triode, we can determine the conductivity type of the tube according to the direction of the PN junction between the base and the other two electrodes.

　　Touch the black lead of the multimeter to the base and the red lead to either of the other two electrodes. If the deflection angle of the meter pointer is large, it indicates that the tested chip transistor is an NPN transistor; if the deflection angle of the meter pointer is small, the tested tube is a PNP type.

　　3. Forward arrow, big deflection

　　Find out the base B and the other two electrodes, which one is the collector C and which one is the emitter e?

　　At this point, we can determine the collector C and the emitter e by measuring the penetration current ICEO.

　　(1) For the NPN chip triode, according to the flow direction of the penetration current of the NPN chip triode, use the black and red test leads of the multimeter to reversely measure the forward and reverse resistances rce and rec between the two poles, although the two measurements , the deflection angle of the multimeter pointer is very small, but careful observation shows that the deflection angle is always slightly larger. At this point, the current flow direction must be:

　　Black probe → C pole → B pole → pole e → red probe, the current direction is exactly the same as the arrow direction in the SMD triode symbol, so at this time, the black probe must be connected to the collector C, and the red probe must be Connect to launch E.

　　(2) The principle of PNP chip transistor is similar to NPN,

　　The current flow must be: black probe → pole → B pole → C pole → red probe, and the current direction is also consistent with the direction of the arrow in the SMD triode symbol. Therefore, at this time, the black probe must be connected to the transmitter E, the red probe must be connected The needle must be connected to collector C.