How to use a multimeter to determine whether a transistor triode is a silicon or germanium tube?
Transistor identification, you can use a multimeter to determine its polarity, to determine whether it is a silicon tube or germanium tube, and at the same time to distinguish between its pins. For general low-power tubes, judgement is generally only appropriate to use R × 1K block. Steps are as follows.
(1) positive and negative measurement.
The red and black pens to measure the transistor resistance of any two pins, and then the red and black pens are still measuring the resistance of these two pins, the two measurements of resistance readings are different, the resistance readings of the smaller measurements is called positive, the resistance readings of the larger measurements is called countermeasurement.
(2) determine the base.
The transistor will be three pins on the 1, 2, 3. Multimeter for three measurements, namely, 1-2, 2-3, 3-1, each divided into positive and negative measurement. These six measurements, there are three positive measurements, and resistance readings are different. Find the positive resistance of the largest pin, such as 1-2, another pin 3 is the base. Since the semiconductor transistor are two diodes connected inversely. Emitter, collector and base of the positive resistance between the general diode forward resistance, very small. When the two pens are connected to the collector and emitter, the resistance value is much larger than the general diode forward resistance.
(3) Discriminate polarity.
Black pen connected to the identified base, red pen connected to another arbitrary pole, if the positive test, then the NPN tube, if the reverse test, then the PNP tube. This is because the black pen is connected to the positive end of the battery in the multimeter, such as positive measurement, the black pen is connected to the P terminal, the transistor is NPN type. If the reverse measurement, the black pen is connected to the N terminal, the transistor is a PNP type.
(4) Determine the collector and emitter.
Positive measurement of the base, for NPN tubes, the black pen is connected to the collector, for PNP tubes, the black pen is connected to the emitter. This is because regardless of positive or negative measurement, there is a PN junction in reverse, most of the battery voltage falls on the reverse PN junction. Emitting junction positive bias, set circuit reverse bias when the flow of current is larger, presenting a smaller resistance. Therefore, for NPN tubes, when the resistance between the collector and emitter is small, the collector is connected to the positive terminal of the battery, that is, connected to the black pen. PNP tube, when the resistance between the emitter is small, the emitter is connected to the black pen.
(5) identify the silicon tube or germanium tube.
The base of the emitter to do positive measurement, if the pointer deflection of 1/2 to 3/5, is a silicon tube. If the pointer deflection of more than 4/5, is the germanium tube. This is because the resistor on the base of the emitter for positive measurement, the voltage added to the base between the emitter is Ube = (1-n/N) E, E = 1.5 V is the battery voltage, N is a linear scale of a DC voltage of the total number of compartments, n is the number of deflection of the needle in the scale of the number of compartments. Usually silicon tube U = 0.6 ~ 0.7 V, germanium tube Ube = 0.2 ~ 0.3 V. Therefore, in the test, for the silicon tube, n/N is 1/2 ~ 3/5; for germanium tube, n/N is about 4/5 or more. In addition, for general small power discrimination, the multimeter should not be used R × 10 or R × 1 block. To 500-type multimeter to measure the silicon tube to illustrate, the internal resistance of the table in the R × 10 block is 100 Ω, the silicon tube b - e pole for the positive measurement, the current up to Ibe = (1.5 - 0.7)/100 = 8 mA, measurement of germanium tubes when the current is also large, with the R × 1 block current is even greater, there may be damage to the transistor. As for the R × 1 K block, the block battery voltage is higher, common 1 V, 12 V, 15 V, 22.5 V and so on several kinds of countermeasurement may cause the PN junction breakdown, so this block should also be used with caution.
