If the marking of a bipolar transistor is erased, you can also determine where it has which pin. To do this, use a device for measuring resistance - an ohmmeter.
Necessary
- - a diode with a known pinout;
- - ohmmeter.
Instructions
Step 1
Determine the polarity of the voltage across the ohmmeter probes. To do this, connect a diode with a known pinout to it, first in one polarity, then in another. When the probes are connected to the diode in polarity, at which the arrow is deflected, a negative probe is connected to the cathode of the diode, and a positive one to the anode. Knowing the polarity of the voltage on the probes, you can begin to determine the terminals of the transistor.
Step 2
Find out which of the conclusions matches the base. There are three ways to connect an ohmmeter to a transistor: between emitter and collector, between emitter and base, between collector and base. Taking into account the fact that in all three cases it can be connected in one or the other polarity, there are six ways in total. The arrow will deflect at one of the polarities of the connection only if the base pin is involved. If the arrow does not deviate for any of the polarities of the connection, then both terminals to which you connect the ohmmeter do not correspond to the base. And the basic one is the rest.
Step 3
Now you can define the structure of the transistor. Connect an ohmmeter in different polarities between the base terminal, the location of which you already know, and one of the remaining. If the arrow deflects when the plus is connected to the base, you have an NPN transistor in front of you. If the deviation occurs when the negative of the ohmmeter is connected to the base, the structure of the transistor is PNP.
Step 4
It remains to find out where the emitter is and where the collector is. For an NPN transistor, connect an ohmmeter between the two non-base terminals. Connect the base to the plus of an ohmmeter. The arrow will deviate. Reverse the polarity of the ohmmeter connection to the non-base terminals. Reconnect the base to the ohmmeter plus. The correct one is the way of switching on, in which the resistance turned out to be lower. In this case, the emitter is connected to negative and the collector to positive. When checking the transistor of the PNP structure, do the same, but connect the base in both cases with the minus of the ohmmeter, and the emitter, when turned on correctly (when the resistance is less), corresponds to the plus of the ohmmeter, and the collector - minus.
