How to determine the pinout of a bipolar transistor. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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How to determine the pinout of a bipolar transistor. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Beginner radio amateur

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In amateur radio practice, it is sometimes necessary to determine the location of the terminals of a transistor (for example, imported), but there is no reference book at hand. Particular difficulties arise when using low-power transistors, in which the design of the collector leads does not have distinctive features. In this case, the pinout of the transistor can be determined by the proposed method.

First, using an ohmmeter, determine the output of the base of the transistor and its structure. On the ohmmeter, set the measurement limit "x10" and alternately connect its probes to pairs of leads, moving in a circle.

Having found when connecting that the resistance between the terminals is small (hundreds of ohms), they transfer the negative probe of the ohmmeter to the remaining free third terminal. If the ohmmeter also detects a low resistance, then the output to which the positive probe of the ohmmeter remained connected is the base, and the transistor structure is n-p-n.

If a large resistance is fixed, the probes are interchanged and, after making sure that the resistance decreases sharply, they come to the conclusion that the base of the transistor is the terminal to which the negative probe of the ohmmeter is connected, and the transistor itself has a p-n-p structure.

It may happen that it will not be possible to find such a conclusion, which would be determined by the indicated method as a base conclusion. This will mean that the transistor is most likely defective.

After determining the base terminal, the ohmmeter probes are connected to the remaining two terminals in arbitrary polarity, assuming that the collector is currently the terminal to which the positive probe is connected (for an np-p transistor) or negative (for a pn-p transistor).

Then a constant resistor with a resistance of 30 ... 50 kOhm is connected to the terminals of the base and the proposed collector. After reading the ohmmeter, change the polarity of the ohmmeter connection and reconnect the indicated resistor between the terminals of the base and the intended collector. After that, the readings of the ohmmeter are again counted. The output of the transistor, when a resistor is connected to which a lower resistance value is obtained, will be the collector, and the remaining "unidentified" output will be the emitter.

It should be borne in mind that usually the positive terminal of the ohmmeter included in the multimeter is the negative terminal of this device.

Author: B.Kandalintsev, Yekaterinburg

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