How to identify the C/E pole of transistor with a multimeter
Usually we can easily find the base electrode b, but which of the other two electrodes is the collector electrode c and which is the emitter electrode e? At this point, we can use the method of measuring the penetration current ICEO to determine the collector c and emitter e.
1. For PNP type transistors
Pinch the b pole and the assumed c pole with our fingers, and use our fingers to act as a resistor between the pins. Connect the black probe to the assumed c pole and the red probe to the assumed e pole, and measure the resistance Rce between the two poles by setting it to R * 1K; Afterwards, the assumed c and e poles will be swapped and tested again. Although the deflection angle of the multimeter pointer is small in both measurements, upon careful observation, there will always be one deflection angle that is slightly larger. At this time, the current flow must be: black probe → e pole → b pole → c pole → red probe, and its current flow direction is also consistent with the arrow direction in the transistor symbol. Therefore, the black probe must be connected to the emitter e, and the red probe must be connected to the collector c.
2. For NPN type transistor
Pinch the b pole and the assumed c pole with your fingers, and use our fingers to act as a resistor between the pins. Connect the black probe to the assumed c pole and the red probe to the assumed e pole. Use a multimeter to set the R * 1K range to measure the resistance Rce between the two poles; Afterwards, the assumed c and e poles will be swapped and tested again. Although the deflection angle of the multimeter pointer was small in both measurements, upon careful observation, there will always be one deflection angle that is slightly larger. At this time, the current flow must be: black probe → c pole → b pole → e pole → red probe. Therefore, at this time, the black probe must be connected to the collector c, and the red probe must be connected to the emitter e.
