A bipolar transistor has three electrodes: an emitter, a collector, and a base. If the pinout of the device is unknown, it can be determined empirically. To do this, you can use a conventional ohmmeter.
Instructions
Step 1
Using a reference diode marked with a pinout directly on the case, determine what is the polarity of the voltage on the ohmmeter probes in resistance measurement mode. In dial gauges, it is often directly opposite polarity, in which it is necessary to connect the probes in the voltage and current measurement modes. On the other hand, digital devices usually have the same polarity in all modes. But it does not hurt to carry out such a check in any case.
Step 2
Connect the probe of the device to one of the leads of the transistor, and then connect the other probe alternately, first to one and then to the other of the remaining leads. If the arrow does not deviate, reverse the polarity of the test leads and repeat the experiment. If it was not possible to achieve the deflection of the arrow in this case, then this conclusion is not basic.
Step 3
Repeat the above steps for the rest of the transistor leads. Find a combination of electrodes in which the transistor behaves similarly to two diodes connected either cathodes or anodes at the same point. The conclusion to which the point of their connection is summed up is the basic one. But remember that you cannot use a transistor as two diodes, since they will affect each other.
Step 4
Determine the structure of the transistor. If it behaves like two diodes connected by anodes, then its structure is n-p-n, and if it behaves like two diodes connected by cathodes, then its structure is p-n-p.
Step 5
It remains to determine which of the remaining leads is emitter and which is collector. Assemble a common-emitter amplifier stage on the transistor. Apply power to it in the correct polarity, depending on the structure (for an n-p-n structure, the voltage on the supply rail should be positive, and for a p-n-p structure, negative). If the transistor is connected correctly (the emitter is on the common wire), its gain will be much higher than with the wrong connection (when there is a collector on the common wire).
