Multimeter measurement to judge the triode mnemonic
Triode tube type and pin discrimination is a basic skill for beginners in electronic technology, in order to help readers quickly master the measurement of judgment methods, the author summarized four phrases of the mnemonic: "three upside down, find the base; PN junction, set the type of tube; along the arrows, the deflection of the big; measurement is not allowed to move the mouth."
1, three upside down, find the base pole
As we all know, the triode is a semiconductor device containing two PN junctions. According to the two PN junction connection is different, can be divided into NPN-type and PNP-type two different conductive types of triode.
To test a triode, use the ohm stop of a multimeter and select the R×100 or R×1k stop. For the pointer type multimeter there, its red pen is connected to the negative terminal of the battery inside the meter, and the black pen is connected to the positive terminal of the battery inside the meter. Assuming that we do not know whether the transistor under test is NPN-type or PNP-type, and can not tell what electrode each pin is. The first step in the test is to determine which pin is the base. At this point, we take any two electrodes (such as the two electrodes for 1, 2), with a multimeter two pens upside down to measure its positive and negative resistance, observe the deflection angle of the needle; then, then take 1, 3 two electrodes and 2, 3 two electrodes, respectively, upside down to measure their positive and negative resistance, to observe the angle of the needle deflection. In these three inverted measurements, there must be two measurements are similar: that is, inverted measurement of the needle deflection, a deflection of a small; the remaining one must be inverted before and after the measurement of the pointer deflection angle is very small, this time the unmeasured pin is that we are looking for the base electrode.
2, PN junction, fixed tube type
After finding the base of the transistor, we can base on the direction of the PN junction between the base and the other two electrodes to determine the conductive type of the tube. The black pen of the multimeter will contact the base, the red pen contact the other two electrodes in any electrode, if the head of the pointer deflection angle is very large, it shows that the measured transistor for NPN type tube; if the head of the pointer deflection angle is very small, then the tube is measured for PNP type.
3, along the arrow, deflection
Find the base b, the other two electrodes which is the collector c, which is the emitter e? At this point we can use the method of measuring the penetration current ICEO to determine the collector c and emitter e.
(1) for NPN-type transistor, NPN-type transistor penetration current flow principle, with the black and red pens of the multimeter inverted measurement of the two poles between the positive and negative resistance Rce and Rec, although the two measurements in the multimeter pointer deflection angle is very small, but observe carefully, there will always be a deflection angle is slightly larger, the flow of current at this time must be: the black pen → c → b → e → red pen, the current flow exactly the same as the symbol of the transistor. Current flow direction is exactly the same as the triode symbol in the direction of the arrow, so this time the black pen must be connected to the collector c, the red pen must be connected to the emitter e.
(2) For PNP-type transistor, the reason is similar to the NPN type, the current flow must be: black pen → e pole → b pole → c pole → red pen, the current flow is also consistent with the direction of the arrow in the symbol of the transistor, so at this time, the black pen must be connected to the emitter e, the red pen must be connected to the collector c.
4、Measure not, move your mouth
If in the "along the arrow, deflection," the measurement process, if due to the reversal of the two measurements before and after the pointer deflection are too small to distinguish, we must "move the mouth". Specific method is: in the "along the arrow, the deflection of the two measurements, with two hands were pinched two pens and the combination of the foot of the tube, with the mouth to contain (or with the tongue against) the base electrode b, still with the "along the arrow, the deflection of the big" method of discrimination can be distinguished from Collector c and emitter e. Which the human body plays the role of DC bias resistance, the purpose is to make the effect more obvious.
