How to judge the quality of triode with multimeter
A, digital multimeter in pn junction block.
The red stylus is connected to B, and the black stylus is connected to E. If the highest digit still shows 1, it means that the emission junction is not feasible and the judgment is bad;
The red stylus is connected to B, and the black stylus is connected to C. If the highest digit still shows 1, it means that the collector junction is blocked and the judgment is bad.
The red stylus is connected to C, and the black stylus is connected to E. If the display becomes a finite number or even drops, it means that the C-E is broken down and the judgment is bad.
Second, the pointer multimeter is placed in X1k electric block.
The black stylus is connected to B, and the red stylus is connected to E. If the stylus does not move, it means that the launch junction is blocked and the judgment is bad;
The black stylus is connected to B, and the red stylus is connected to C. If the needle does not move, it means that the collector junction is blocked and the judgment is bad.
The black stylus is connected to C, and the red stylus is connected to E. If the stylus swings, it means that the C-E is broken down and the judgment is bad.
The triode can be judged by the following methods:
1. Distinguishing method of base and tube type:
The measurement of germanium tube is in the range of R×100, and that of silicon tube is in the range of R×1K. First, fix the red stylus in contact with any leg, and then measure the other two legs with the black stylus. See if you can measure the smaller resistance twice. If you can't move the red stylus to other feet, you can continue to measure two small resistances. If you can't find two small resistances by fixing the red stylus, you can fix the black stylus to continue searching. When two small resistors are found, the foot used by a fixed stylus is the base.
If the fixed stylus is a black stylus, the triode is NPN, and if the fixed stylus is a red stylus, the transistor is PNP.
2. Distinguish the collector:
Because when the emitter and collector of triode are connected correctly, β is large (the swing amplitude of the watch hand is large), β is much smaller when it is connected reversely. Therefore, let's assume a collector connected with an ohmic switch (for PNP tube, the emitter is connected with a black stylus and the collector is connected with a red stylus). When measuring, pinch (or connect) the base and the assumed collector by hand, and the two poles can't touch. If the pointer swings a lot, but the pointer swings a little after the two poles are switched, it means that the assumption is the correct collector, so as to determine the collector and emitter.
Either there is something wrong with the multimeter or the triode is broken according to the resistance value you mentioned above. Let's find a good triode and measure it according to the above method before comparing it, so that we can judge whether it is good or not and sum up our experience.
The pin of the transistor must be correctly identified, otherwise, the access circuit will not work normally, and the transistor may be burnt out. Knowing the type and electrode of triode, pointer multimeter's method of judging transistor is as follows:
① Measuring NPN triode: place the multimeter at R × 100 or R × lk, connect the black stylus to the base, and connect the red stylus to the other two poles successively. If the resistance values measured twice are small, connect the red stylus to the base and connect the black stylus to the other two poles successively. If the resistance values measured twice are large, the triode is good.
② Measuring PNP triode: place the multimeter at R × 100 or R × lk, connect the red stylus to the base, and connect the black stylus to the other two poles successively. If the resistance values measured twice are small, connect the black stylus to the base and connect the red stylus to the other two poles successively. If the resistance values measured twice are large, the triode is good.
When the mark on the triode is unclear, a multimeter can be used to preliminarily determine the quality and type of the triode (NPN or PNP), and to identify the three electrodes, E, B and C.. The test method is as follows:
① use pointer multimeter to judge the type of base B and triode: put the multimeter at R × 100 or R×lk, first assume one pole of the triode as the base, connect the black stylus to the assumed base, and connect the red stylus to the other two poles successively. If the resistance values measured twice are very small (or about several hundred ohms to several thousand ohms), then the assumed base is correct, and the triode under test is an NPN type tube; As above, if the resistance values measured twice are very large (about several thousand ohms to several tens of thousands ohms), then the assumed base is correct, and the transistor under test is PNP-type. If the resistance value measured twice is one big and one small, the original assumed base is wrong. At this time, the other electrode must be re-assumed as the base, and then the above test is repeated.
② Judge the collector C and the emitter E: still place the pointer multimeter ohm at R × 100 or R × 1k. Take the NPN tube as an example, connect the black stylus to the hypothetical collector C and the red stylus to the hypothetical emitter E, and hold the B and C poles by hand (it is not possible to make direct contact between B and C). Through the human body, connect a bias resistor between B and C, read the resistance shown in the meter, and then connect the two pens in reverse. If the resistance measured for the first time is smaller than that for the second time, the original hypothesis is established, because the small resistance values of C and E indicate that the current passing through the multimeter is large and the bias is normal. Nowadays, pointer multimeters have interfaces for measuring triode magnification (Hfe). You can estimate the magnification of the triode.
