Transistor tester & emitter voltage

[Daniel M]

Hi there, I'm using the Analog Discovery 3 in conjunction with the transistor tester add-on board to profile a selection of transistors. I notice that one of the options apparently sets the emitter voltage, but it is unclear whether this actually sets the voltage at the emitter. When tested using a 2N3904, the base current is consistent with a Vbe of ~0.75V, and an emitter at ground - regardless of the emitter setting.

Could you please clarify what the emitter setting actually does in the tracer settings?

Thanks!

[attila]

Hi @Daniel M

It is not isolated.
The base and collector is controlled by W1 and W2 which generate signals relative to the emitter (virtual ground). If this is set to -5V by the V- power supply, the W1 and W2 for 0V output -5V. The transistor will receive signals from 0V to +10V relative to its emitter. Similarly, the emitter can be set to +5 by the V+ power supply, to have 0V to -10V

[attila]

Hi @Daniel M

The device AWG outputs +/-5V and by brining the emitter (virtual ground) to -/+5V it lets you test the components in 0.. +/-10V range. This is default option with Adapter.

[Daniel M]

Hi @attila, thanks for your reply. I understand that this changes the range of voltages that can be applied at the collector, but am wondering whether this is actually electrically isolated from the base - reading the documentation, the implication is that the emitter voltage is offset, which would then change the base-emitter voltage (and thus the base current), but this doesn't seem to be the case.

Is it the case that the virtual ground applied here is only for the collector connection, and that this is isolated from the base-emitter node?

[Daniel M]

Hi @attila, ah right, thanks for explaining that! That makes sense.