What does the vertical line in this equation mean?

[APUGYael]

Hey,

What does the vertical line with the "I_b" on the bottom right mean?
Link here: https://imgur.com/a/nII9g

Thanks,

-Yael

 

[gleem]

I believe it means the ratio is evaluated at a constant I_b

 

[fresh_42]

It usually means "evaluated at". It indicates the point where derivatives are calculated to actually turn into a linear approximation. As there is no derivative, I assume that either $c$ is approaching $b$ or at least $b \in I_c$ and $I_c$ is closing down on $\{b\}$.

For the record, the image reads $r_{ce} = \left.\dfrac{\Delta U_{ce}}{\Delta I_c}\right|_{I_b}$ but maybe it means something else, as it looks like a physical equation.

 

[gleem]

@fresh_42 I believe the equation is the dynamic emitter collector resistance for a bipolar transistor. in this case the ratio of the change in emitter collector voltage over the change in the collector current.

 

[fresh_42]

@fresh_42 I believe the equation is the dynamic emitter collector resistance for a bipolar transistor. in this case the ratio of the change in emitter collector voltage over the change in the collector current.

I suspected something like this. Actually I had a déjà vu as I wrote the answer, which was why I added the physical possibility. Strange thing.