I have one of these cheapo GM328A transistor testers & I'm diagnosing Darlington transistor with it. It's printing these parameters \$ICE0\$, \$ICEs\$ & \$B\$, which I'm not sure what they mean:

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I have a suspicion \$ICE0\$, \$ICEs\$ are just CE leakage currents when \$V_B = 0\$. Then there's \$B\$. Is that just \$B_f\$?? Because according to the datasheet, it's a minimum of 5000.


1 Answer 1


\$I_{ceo}\$ (note that it's o, not 0) is the collector-to-emitter current when the base is open. This is one measurement of the transistor's leakage current.

\$I_{ces}\$ is the collector-to-emitter current when the base is shorted to emitter. This is another leakage characteristic.

\$β\$ (β, not B) is the transistor's current gain, \$\frac{I_c}{I_b}\$. It's also called \$h_{FE}\$.

As for why β is so much lower than the datasheet number, I would guess because the tester isn't designed to measure Darlington pairs like this, and can't interpret such a high number. It's possible some digits got cut off, and the number is actually 13400 or something. Or it's possible that, at the low test current this device uses (who knows what it is, but it's probably no more than a few μA), the β actually is 134--the datasheet number is specified at 10 A of collector current, far more than this thing can probably provide.

For completeness' sake, the other parameter listed, \$U_f\$ is the forward voltage of, most likely, the base-emitter junction. Or junctions, as it's a Darlington. This is usually written as \$V_f\$ in my part of the world, but \$U_f\$ is common in Europe and Asia. Since there's apparently a 70 Ω pull-down resistor in there (according to the datasheet you linked), I don't think the number it gives you is likely to be that useful.

The tester seems to have also erroneously identified an emitter-collector diode; the datasheet makes no mention of this, and while there are BJTs that have one, it's pretty uncommon--you see that more often with IGBTs (and there's the inherent diode in a MOSFET, of course, but that's not added intentionally).

  • \$\begingroup\$ Thanks for the answer. I've been looking at the schematics (dragaosemchama.com/wp-content/uploads/2019/04/sch2.png) to find a way to supply enough, in case of BJTs, current to the collector; in the case of MOSFETs, current to drain; & in the case of zeners voltage across. I would think in my admittedly amateur mind, the multiplexing & analog signals are done on different chips. But, no, it's nearly all done in the microcontroller. \$\endgroup\$ Commented Mar 28 at 8:57
  • \$\begingroup\$ Would anybody have any idea how to provide higher voltage/current to components? Routing the PB[5:0] of ATmega328P to some homebrew circuit & updating the source code is too much of a challenge to me... Looks like it can't be done. \$\endgroup\$ Commented Mar 28 at 9:02
  • \$\begingroup\$ @TempusNomen If you want to test a part at higher current, I would test it with a proper curve tracer or parameter analyzer, but I have easy access to 370A and a B1505A through work. \$\endgroup\$
    – Hearth
    Commented Mar 28 at 13:18

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