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| Question on NPN Logic Inverter From Textbook |
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| eev_carl:
Hi, I created an LT Spice of this logic inverter from a textbook (Jaeger and Blalock, 3rd edition "Microelectronic Circuit Design"). I'm getting a Vce that's 10x less than what's printed in the book. I was wondering if someone could help troubleshoot my model. In the sim, I get a Vce of 18mV and the book (see attachments) has it listed at 180mV. Maybe I'm not measuring the right thing? Thanks, Carl |
| eev_carl:
It's cut off in the photo, but the figure from the book below the text is 5.32(a). |
| Wimberleytech:
Pick a 2n3904 model for you simulation and see what you get. You are being kinda hard on that poor transistor forcing 1 volt Vbe. Add some base resistance. |
| eev_carl:
2n3904 V(vce): 0.00810523 voltage |
| rstofer:
VceSat is usually on the order of 0.2V (MAX at Ic=10 mA). Your simulation shows about 1/10th that amount and it is probably an issue with the model. Look at the 2d page of the 2N3904 dataseet and you will see that VceSat is also a function of collector current. The lower the current, the lower the saturation voltage. https://www.onsemi.com/pub/Collateral/2N3903-D.PDF Page 6 shows VceSat of 0.1V for currents less than about 10 mA. Try it with a real circuit! |
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