The identification of the tube type and the pin of the triode is a basic skill of the beginners of electronic technology. In order to help the reader quickly grasp the method of measurement and judgment, the author sums up four sentences: "three reverses, find the base; PN junction, fixed type; Follow the arrow, the deflection is large; the measurement is not accurate, move the mouth." Let us explain it step by step.
One or three are reversed, and it is known to the great base that the triode is a semiconductor device containing two PN junctions. According to the different connection modes of the two PN junctions, it can be divided into two types of transistors of different conductivity types: NPN type and PNP type.
Test the triode to use the ohmic block of the multimeter and select the R×100 or R×1k gear. For the pointer type multimeter, the red pen is connected to the negative pole of the battery in the watch, and the black pen is connected to the positive pole of the battery in the watch. Suppose we don't know whether the measured triode is NPN or PNP, and we can't tell what electrode each pin is. The first step in the test is to determine which pin is the base. At this time, we take two electrodes (such as the two electrodes are 1, 2), measure the positive and negative resistance of the meter with two meter pens upside down, observe the deflection angle of the hands; then, take 1 3 electrodes and 2, 3 electrodes, respectively, measure their positive and negative resistances upside down, and observe the deflection angle of the hands. In these three inversion measurements, there must be two measurements that are similar: that is, the needle is deflected once in the reverse measurement, and the deflection is small at one time; the remaining one must be reversed before and after the measurement, the pointer deflection angle is very small, this time the unmeasured one The pin is the base we are looking for.
Second, the PN junction, the fixed tube type to find the base of the 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. The black test pen of the multimeter is in contact with the base, and the red test pen contacts any one of the other two electrodes. If the deflection angle of the head pointer is large, the measured triode is an NPN type tube; if the deflection angle of the head pointer is small, Then the tube to be tested is PNP type.
Third, along the arrow, the deflection is large to find the base b, the other two electrodes which is the collector c, which is the emitter e? At this time we can use the method of measuring the penetration current ICEO to determine the collector c and the emitter e.
(1) For the NPN type triode, the principle of the flow direction of the NPN type triode through the current, using the black and red test leads of the multimeter to measure the positive and negative resistances Rce and Rec between the two poles, although the multimeter pointer in two measurements The deflection angle is very small, but when you look closely, there will always be a slight deflection angle. At this time, the current flow must be: black test pen → c pole → b pole → e pole → red test pen, the current flow is exactly in the triode symbol The direction of the arrows is the same, so the black pen must be connected to the collector c, and the red pen must be connected to the emitter e.
(2) For the PNP type triode, the reason is similar to the NPN type, and the current flow direction must be: black test pen → e pole → b pole → c pole → red test pen, and its current flow direction is also consistent with the direction of the arrow in the triode symbol. Therefore, at this time, the black test pen must be connected to the emitter e, and the red test pen must be connected to the collector c.
Fourth, the measurement can not be made, if the mouth is in the process of "following the arrow, the deflection is large", if the deflection of the two measurement pointers before and after the inversion is too small to distinguish, it is necessary to "move the mouth". The specific method is: in the two measurements of "shun arrow, large deflection", use two hands to pinch the joint between the two test leads and the pin, and use the mouth to hold (or with the tongue against) the base electrode b, still The collector c and the emitter e can be distinguished by the discriminating method of "following the arrow and deflecting large". The human body acts as a DC bias resistor in order to make the effect more obvious.
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