| Electronics > Beginners |
| Question on NPN Logic Inverter From Textbook |
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| Wimberleytech:
Born in the lab |
| Wimberleytech:
--- Quote from: eev_carl on September 30, 2019, 04:19:27 pm --- --- Quote from: Zero999 on September 30, 2019, 04:05:55 pm ---That's better. I was just about to post the same schematic, but with R2 = 8k2, but you beat me to it. I suggest you try it. --- End quote --- Is there a rationale for selecting 8.2k? Also, is this R a current limiting resistor or DC coupling (or both)? --- End quote --- Power, speed... The resistor is to limit current. All resistors couple dc. |
| edavid:
--- Quote from: eev_carl on September 30, 2019, 03:54:37 pm ---Is the general consensus that the book is wrong? High current / low current, the book still seems about an order of magnitude too high (180mV versus 18mV)? --- End quote --- I wouldn't say that the book is wrong. They are just describing a different type of transistor, probably something more like a 2N2369. You can tell this from the high VBE. Also, your base current is still unrealistically high. Try a forced beta of around 10 and see what you get. |
| Wimberleytech:
--- Quote from: edavid on September 30, 2019, 04:26:54 pm --- --- Quote from: eev_carl on September 30, 2019, 03:54:37 pm ---Is the general consensus that the book is wrong? High current / low current, the book still seems about an order of magnitude too high (180mV versus 18mV)? --- End quote --- I wouldn't say that the book is wrong. They are just describing a different type of transistor, probably something more like a 2N2369. You can tell this from the high VBE. Also, your base current is still unrealistically high. Try a forced beta of around 10 and see what you get. --- End quote --- At best, the book is incomplete then. Given that it's goal is to teach, leaving the student with such a quandary without explanation is sub optimal. But, books are never perfect. |
| fourfathom:
--- Quote from: Wimberleytech on September 30, 2019, 04:35:29 pm ---At best, the book is incomplete then. Given that it's goal is to teach, leaving the student with such a quandary without explanation is sub optimal. But, books are never perfect. --- End quote --- That book is quite complete (I found it online as a pdf). Take a look at Chapter 5 (Bipolar Junction Transistors) where the behavior in saturation is extensively discussed. That "inverter" example is just that, en example of an inverter, and not meant to by itself be a treatise on transistor characteristics. So from this the OP learns that not all transistors are created equal. Not a bad lesson! |
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