6-
17
similar to a diode with its polarity reversed. These are the signatures we expected from our
circuit modeling. We can do the same kind of comparison with the emitter-base circuits.
Zener Diode 1N5239B PNP Transistor 2N3906 NPN Transistor PN2222A
5V, 10kΩ
ΩΩ
Ω Range
Figure 6-23. Signature of a Diode and Emitter-Base of a Transistor
We can see that the base-emitter signature of the NPN transistor is nearly identical to the
signature of the zener diode. The emitter-base signature of a PNP transistor is also nearly
identical but opposite in polarity to the zener diode.
PNP Transistor - 2N3906 NPN Transistor - PN2222A
15V, 10kΩ
ΩΩ
Ω Range
Figure 6-24 Signature of the Collector-Emitter of a PNP and NPN Transistor
Emitter to Common
You can see that the collector-emitter signature of a PNP transistor looks like a forward biased
diode with the knee at approximately +7 Volts. The collector-emitter signature of a NPN
transistor looks similar to a reverse biased diode with the knee at approximately -7 Volts.
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