I happened to use a high-gain, small signal BJT (2N5088) in my testing and observed intermittent issues with the Tester's reported hFE. Most of the time, the Tester responds with very reasonable hFE for my transistor as follows:
NPN
hFE 520 c
I_E 2.742 mA
Vbe 618 mV
Fortunately, my testing repeated this measurement several times. After a while, the Tester would respond with much too high hFE for this transistor as follows:
NPN
hFE 6123 c
I_E 6.671 mA
Vbe 621 mV
I looked at the code closely and observed that the Tester is applying Vcc (5 volts) with Rl (680 ohms) to the collector-base (C-B) junction (this is normal and okay). There are times where the Tester applies this signal to the emitter-base instead; this can be a problem with Super-Beta BJT's because the reverse breakdown potential is low (e.g. for 2N5088 breakdown is 4.5 volts). In my case, it seems that my transistor broke-down after many tests.
I have read that the forward gain of Super-Beta BJT's will degrade once the transistor has been operated in reverse emitter-base breakdown. Ideally, the Tester should only apply Vcc/2 (i.e. about 2.5 volts) to C-B and E-B junctions until the Tester determines the proper orientation and then it can use full Vcc (5 volts) on the C-B junction.
An alternate solution might be to use Rh (470 k ohms) on the C-B and E-B junctions and then switch to Rl (680 ohms) when the proper orientation is found? The emitter-base junction may still break down in this case, however, the low resulting current might save the transistor some stress.
I'm continuing to play with this and I might be able to work-in some changes for release V1.54m? Until then, I just wanted people to know of this potential issue.
I happened to use a high-gain, small signal BJT (2N5088) in my testing and observed intermittent issues with the Tester's reported hFE. Most of the time, the Tester responds with very reasonable hFE for my transistor as follows:
NPN
hFE 520 c
I_E 2.742 mA
Vbe 618 mV
Fortunately, my testing repeated this measurement several times. After a while, the Tester would respond with much too high hFE for this transistor as follows:
NPN
hFE 6123 c
I_E 6.671 mA
Vbe 621 mV
I looked at the code closely and observed that the Tester is applying Vcc (5 volts) with Rl (680 ohms) to the collector-base (C-B) junction (this is normal and okay). There are times where the Tester applies this signal to the emitter-base instead; this can be a problem with Super-Beta BJT's because the reverse breakdown potential is low (e.g. for 2N5088 breakdown is 4.5 volts). In my case, it seems that my transistor broke-down after many tests.
I have read that the forward gain of Super-Beta BJT's will degrade once the transistor has been operated in reverse emitter-base breakdown. Ideally, the Tester should only apply Vcc/2 (i.e. about 2.5 volts) to C-B and E-B junctions until the Tester determines the proper orientation and then it can use full Vcc (5 volts) on the C-B junction.
An alternate solution might be to use Rh (470 k ohms) on the C-B and E-B junctions and then switch to Rl (680 ohms) when the proper orientation is found? The emitter-base junction may still break down in this case, however, the low resulting current might save the transistor some stress.
I'm continuing to play with this and I might be able to work-in some changes for release V1.54m? Until then, I just wanted people to know of this potential issue.