Formula for measuring triode base with multimeter
Triode type judgment and pin judgment belong to the electronic foundation, and ordinary beginners in electrical technology will be exposed to three inversions to find the base; PN junction, fixed tube type; Along the arrow, large deflection; Not sure, move your mouth. Maybe it's much easier. Of course, it's useless to recite the formula without knowing its meaning.
Method for measure triode base by multimeter
As we all know, triode is a semiconductor device with two PN junctions (not two PN junctions in series). According to the different connection modes of two PN junctions, triodes can be divided into NPN type and PNP type.
The test of triode is to use the ohm block R×100 or R×1k of the multimeter. The pointer multimeter, the red pen is the negative electrode of the multimeter, and the black pen is the positive electrode of the multimeter battery. When testing the transistor type, the first step is to judge the base position of the pin. Measurement method: randomly select two electrodes (such as 1 and 2), first measure the positive and negative resistance and observe the deflection angle of the hands; Next, take the sum of 1 and 3 electrodes.
2, 3 two electrodes, respectively, upside down to measure their positive and negative resistances, and observe the deflection angle of the hands. In these three inverted measurements, there must be two similar results: that is, in the inverted measurement, the first deflection of the watch hand is large and the first deflection is small; The remaining time must be that the deflection angle of the pointer is very small before and after the reverse measurement, and this time the untested pin is the base we are looking for.
Circuit symbols of NPN transistor (left) and PNP transistor (right)
After appeal measurement, after we determine the base of the pin, we can determine the tube type according to the direction of the PN junction between the base and the other two electrodes. Measurement method: put the black stylus of multimeter at the base and the red stylus at any other electrode. If the deflection angle of the pointer of the multimeter is large, it means that the transistor under test is NPN-type. If the deflection angle of the meter pointer is small, the tube under test is PNP type.
And the tube type found after passing through the base B, then we can judge the collector C, so which is the emitter E?
Structure and current direction of NPN triode
NPN triode: According to the principle of the flow direction of the penetrating current of NPN triode, the positive and negative resistances Rce and Rec between the two poles are measured with the black and red pens of the universal meter upside down, and the two measurement results are obtained. It is found that the deflection of the pointer on the meter head is small. After careful observation, it is found that the deflection angle is a little larger once, that is, the current flow direction is: black pen →c pole →b pole →e pole → red pen, and the flow direction coincides with the direction of the transistor symbol arrow.
Structure and current direction of PNP triode
PNP transistor: The principle is the same as measuring NPN transistor. After testing, the results are obtained at this time: black pen →e pole →b pole →c pole → red pen. Similarly, the current flow direction coincides with the direction of the transistor symbol arrow, so it can be concluded that "so the position of black pen is emitter E at this time, and the side of red pen is collector C." .
Physical diagram of triode and its internal structure and symbols
In the measurement process of the third formula, it is impossible to tell which time the deflection pointer is larger, so it is necessary to move your mouth. So how do you talk? When measuring the formula of the third sentence, hold the joint between the red and black pen and the pin with both hands, then hold the base electrode B with your mouth (tongue touching is also acceptable), and then compare the results twice. Because the human body acts as a DC bias resistor, the two comparisons will become more obvious.
PS: the method used in the third sentence of the formula is to measure the penetration current ICEO, which is used to identify the collector c and emitter e.
