What is Early Voltage? (066f)

[@spheretical3609]

Very appreciative of the practical nature of your videos and subsequent advice or findings. Your increasing production values are noticed and appreciated.

[@eie_for_you]

Thank you so much! I'm always looking to do it better. Never stop learning! 🙂

[@RensePosthumus]

This was a good and fine video for the day. Thanks.

[@eie_for_you]

You are welcome! 🙂

[@uncleTedLol]

This is brilliantly presented, thanks for your sharing your expertise!

[@eie_for_you]

Thanks! 🙂

[@kensmith5694]

I think a slightly better way to explain what is going on is to come at it like this: The current flows into the emitter following the diode equation for the E-B junction. Most of that current goes out the collector but some goes out the base according to the HFE. The HFE of a transistor depends on the effective thickness of the base. Depletion regions don't count as part of the base so higher collector voltage makes the base appear thinner. How rapidly the collector depletion region is narrowing the base is what determines the slope of the collector current lines. In theory, (but not in practice) the narrowing of the base should be raising the HFE regardless of current so the lines should all meet at the mythical place called the early voltage on the Ic=0 line.

[@daveengstrom9250]

Feel better now? You did not listen.

[@kensmith5694]

@@daveengstrom9250 I think you missed the meaning of my comment. Read it again. I made what I believe are several important points that make the explanation work better.

[@eie_for_you]

Yes, I believe that is exactly what I said in the video, though I didn't rope in the effects on hFE ... at least not directly. 🙂

[@kensmith5694]

@@eie_for_you My comment also put the points in a different order that I think works better. Getting the changing HFE up front explains the change in collector current as a change in HFE

[@eie_for_you]

@@kensmith5694 But, the change in hFE was not the point, but a side observation in the explanation of what it is all about.

[@WECB640]

This was fantastic! Ralph, I'd never heard of "early voltage" before. Thank you for explaining. Also, it was eye opening to learn that the linearity of a transistor changes because of this early effect. I know what I'm about to say uses the wrong terminology, but it's almost like the transistor has an inherent "Q", and that it's variable. Perhaps what I should say is Beta, not Q. My mind then asks the question....do vacuum tubes also have an "early voltage", or does this only pertain to low impedance current driven devices? Looking forward to your reply. 73 OM

[@eie_for_you]

Thanks! I'd learned of all of this back when I was in engineering college, but had forgotten a lot of it through disuse. It is nice to have this stuff now coming back. I think vacuum tube have their own brand of things like this including the Miller Effect which affects semiconductors, too. (that is in the next video). Because of the nature of the Early Voltage, I think this is specific to semiconductor devices and, maybe, to BJTs in specific. 🙂

[@daveengstrom9250]

Is it possible to learn about Early voltage late in life? (educational impedance).

[@eie_for_you]

LOL!!!🤣🤣🤣🤣

[@ornithopterindia]

👍Thank you sir.

[@eie_for_you]

You are welcome, my friend. 🙂

[@newmonengineering]

I have never needed that early voltage to make my calculations, that said I can do all my calculations on a napkin with rough estimates and am within 10% or less every time. And at that point I am within tolerance for most circuits. Its rare that you have to have an exact calculation for an exact input and output. As long as its about where you want it, the circuit will work. You can always add more stages if you need more output. Its easier to build another stage than to worry about calculating exact numbers only to find your resister tolerance throws the numbers off anyway.

[@eie_for_you]

Yeah and neither have I. You rightly point out that by the time we add all of the tolerances of real life resistors and capacitors, precise calculations with transistor models are pretty much moot. Besides, even there ... the hFE possibilities of a particular transistor part number alone cover huge amounts of territory especially when we add in thermal considerations. It is a painfully imprecise world, my friend. 🙂

[@clytle374]

Thanks, that was one of those things that bothered my every time I saw it.

[@eie_for_you]

You are welcome! 🙂

[@derdoktor7123]

I really like your videos! You are presenting very ”dry“ theory in a very good way. But plz do me a favor, you are using too often the left or right turn on your chair, I‘m watching your videos and the only thing I‘m awaiting during your show is this left or right turn… May be there is something new you can do to suprise us!

[@eie_for_you]

Ya know ... that is a good point! I've been thinking about that. Stay tuned for the second video on the CASCODE Amplifier for something new and different. 🙂

[@RensePosthumus]

I've watched the video again, but something is nagging me. You've showed clearly that theory (all curves interact in one point) and practices (curves intersect x-axis at different points) don't agree. But there is no explanation on the *why* there is this disagreement. Could you explain that in another video?

[@eie_for_you]

I thought for absolutely *sure* I already replied to this. :-/ Well, let me give it another try. Understanding the why behind the disparity between theory and practice is one of those mysterious semiconductor physics "rabbit holes." No one seems to want to admit the disparity in the first place. If they tipped their hand on this one back when I had to take 2 semesters of this in engineering school, I remember none of it (it was 43 years ago!). The good news is, in practical terms, we actually rarely need to know the Early Voltage or even use it if we knew it. :-)