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Circuit 8: Determining the connection sequence of a NPN transistor
Setup information
Install the transistor as shown in Fig. 2.8. After that, install all other resistors. Now it is time for the jump-
ers. For the purpose of identification, the measuring leads are shown in the figure in black or red. Feel free
to use your own colours. Then connect the moving-coil instrument. Check the placement on the board again
and only then connect the battery.
Experiment
Connect the red line first. Then with the black line touch the remaining two transistor terminals one after
the other. Repeat this until the red line connection is located at the terminal of the other two transistor
connections where the moving-coin instrument measures the greater voltage deflection. All other connec-
tion combinations should show a smaller deflection on the meter; if this is not happening, the transistor is
faulty. The red line indicates the base connection of an NPN transistor.
This method works with silicon and germanium transistors, but only with bipolar transistors and not with
FET transistors.
The circuit diagram for this experiment is shown in Chap. 3, Fig. 3.8.
Components required:
1 x 2N3904 transistor,
1 x 470 Ω resistor,
2 x 1 kΩ resistors,
2 x 10 kΩ resistors,
1 x moving-coil instrument,
1 x breadboard, 1 x 9V bat-
tery with clip connector
Fig. 2.8: Determining the connec-
tion sequence of a NPN transistor
33
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