I need to calculate the current gain of a NPN BJT, and I have done an experiment where the voltage Vbe is increased slowly in steps and the resulting Ib and Ic are recorded. The voltage between collector and emitter is kept at a constant 5V. hfe should equal Ic/Ib, but I get very small values < 1 for hfe like 0.1, which seems wrong. In the data Ib goes from 10uA to 50uA, and Ic goes from .4uA to 5.7uA. Have I just done something completely wrong? or am I missing something?

Many thanks

My Data

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  • \$\begingroup\$ How are you taking the measurements? Are you sure the scale isn't off? \$\endgroup\$ – loudnoises Dec 6 '18 at 19:28
  • \$\begingroup\$ Are you sure your Ic measurements aren't in mA? That would make more sense. Additionally, looking at the datasheet of the 2N3053, it looks like it's not designed to operate at such low currents, though I doubt it would be this bad. \$\endgroup\$ – Hearth Dec 6 '18 at 19:32
  • \$\begingroup\$ You write that you slowly increased the \$V_\text{BE}\$ voltage, but your chart shows perfectly stepped \$I_\text{B}\$. I'm finding it difficult to believe you managed that by adjusting \$V_\text{BE}\$. In any case, you need to show us the circuit by which you created those results and the method you used to take measurements. Such details are important if you want an answer. As it is, assuming you really did get those measurements accurately I'd guess your BJT was deeply saturated. \$\endgroup\$ – jonk Dec 6 '18 at 20:06
  • \$\begingroup\$ loudnoises and Hearth, You both have a point, it could be a simple case of me being stupid and writing uA when I meant mA. I think that is the most likely explanation. When I change Ic to mA I get hfe values closer to 100 which is reasonable. Thanks for pointing that out! \$\endgroup\$ – Eric Navarrete Dec 6 '18 at 21:42
  • \$\begingroup\$ @jonk You are correct, actually I adjusted Vbe to get Ib in 10uA intervals, the power supply is quite accurate, so I was able to get it very very close to 10uA intervals. I added a schematic to the original post if anyone wants to see it \$\endgroup\$ – Eric Navarrete Dec 6 '18 at 21:51

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