What's the input impedance at the base? Beta times the emitter resistor. Assume a beta of about 100, that means we have about a quarter-megohm at the base. Less than 1% effect on the biasing. And the beta of the 2N4401 is higher than that. When I picked a random one from my parts box and measured it with a milliamp of quiescent current, the beta was about 240.
@@KludgesFromKevinsCave Understood. Thank you !!.. If possible, please show the mathematical derivations and its demonstrations for calculation of Input and Output Impedances of BJT.
@@VigneshD25 This early on in the series, I'm focusing on what the circuits do, rather than working out the numbers in detail. In episode 5 ruclips.net/video/AIxc-cQqKHA/видео.html I introduce transistor beta, which starts letting us calculate impedances. For the common-emitter amplifier, I come back and run more detailed numbers in episode 7. I hope you enjoy the rest of the series!
I am 66, and for the 1st time in my life learning electronics in right earnest. I really love your lessons. And BTW, What is the Spice software that you are using Sir?
I'm using CircuitJS (www.falstad.com/circuit/circuitjs.html) to do the simulations. It's free and runs in the browser. Where I have circuit simulations in the video, I try to include the CircuitJS links in the description and on the project GitHub, so that viewers can follow along with the exact models I used.
Well, 0:20 contradicts your explanation for the valve analogy from the previous video, in which you clarified the valve as behaving like a resistor control, not a current control. But here you switch back to valve controlling the current analogy (by telling it controls "more or less current to flow" while the current was constant in the previous video, hence the name "constant current source")
The constant current source has a constant current at the base, hence a constant current at the emitter. What's actually going on is a feedback loop. If the output current drops, that means that the voltage across the emitter resistor will drop, which increases the current through the base, opening the valve and allowing more current to flow.
I would like to see a video of using the X/Y mode on the scope and the sweep mode of a function generator. I have both and have never used either (X/Y mode and sweep). I think we have the same models of each instrument. As an aside your voice volume varies quite a bit and would benefit from some normalization. Thank you for the video!
@justovision X/Y on the scope is in the video about Schmitt triggers, demo-ing the hysteresis loop. Sweep on the function Gen will come when I start on filters. Stay tuned!
Thanks for the remarks about the audio. I was using an audio compressor in 'kdenlive' but owing to a misconfiguration, it wasn't actually compressing. It'll be a few weeks before the problem's fixed - I try to run a 4-6 video backlog - but I'll try to be more careful moving forward. Still learning this video stuff!
Flexing your 60k counts meter, the yellow one looks to be 10k counts. Nice. Cant wait to get a better look at your scope. Edit: only had to watch a little further. I'm a big fan of Rigol.
The yellow meter is one I got when I was in grad school in the 1980's, on a grad-student budget. It still works. The lack of auto-ranging is annoying, but it's fine as a second meter. Rigol has a lot of bang for the buck. I picked it out because that's the scope I seem to see on half the electronics-hacker RUclips channels I watch, and the other ones I see are all at least twice the price. I've only a few complaints so far, relating to some really weird quantization artifacts. (The values appear to be quantized once in the A/D, and then again going to the screen, with the result that on some scales, there are screen pixels that never light.) One of these months I want to do a video or three on restoring the Tektronix analog oscilloscope that I picked up at a surplus auction in the 1980s.
Oh, the other night I got curious and watched where the ranges of the meters switch. The old yellow meter is a 20k count meter, but the current ranges go in steps of 100x. The blue meter is indeed 65536 counts.
![BLACK BAG - Official Trailer [HD] - Only in Theaters March 14](http://i.ytimg.com/vi/Du0Xp8WX_7I/mqdefault.jpg)
At 8:00 when calculating input impedance, apart from R1 || R2, can we ignore the input resistance looking into the base of the BJT ?
What's the input impedance at the base? Beta times the emitter resistor. Assume a beta of about 100, that means we have about a quarter-megohm at the base. Less than 1% effect on the biasing. And the beta of the 2N4401 is higher than that. When I picked a random one from my parts box and measured it with a milliamp of quiescent current, the beta was about 240.
@@KludgesFromKevinsCave Understood. Thank you !!.. If possible, please show the mathematical derivations and its demonstrations for calculation of Input and Output Impedances of BJT.
@@VigneshD25 This early on in the series, I'm focusing on what the circuits do, rather than working out the numbers in detail. In episode 5 ruclips.net/video/AIxc-cQqKHA/видео.html I introduce transistor beta, which starts letting us calculate impedances. For the common-emitter amplifier, I come back and run more detailed numbers in episode 7. I hope you enjoy the rest of the series!
I am 66, and for the 1st time in my life learning electronics in right earnest. I really love your lessons. And BTW, What is the Spice software that you are using Sir?
I'm using CircuitJS (www.falstad.com/circuit/circuitjs.html) to do the simulations. It's free and runs in the browser. Where I have circuit simulations in the video, I try to include the CircuitJS links in the description and on the project GitHub, so that viewers can follow along with the exact models I used.
Well, 0:20 contradicts your explanation for the valve analogy from the previous video, in which you clarified the valve as behaving like a resistor control, not a current control.
But here you switch back to valve controlling the current analogy (by telling it controls "more or less current to flow" while the current was constant in the previous video, hence the name "constant current source")
The constant current source has a constant current at the base, hence a constant current at the emitter. What's actually going on is a feedback loop. If the output current drops, that means that the voltage across the emitter resistor will drop, which increases the current through the base, opening the valve and allowing more current to flow.
I would like to see a video of using the X/Y mode on the scope and the sweep mode of a function generator. I have both and have never used either (X/Y mode and sweep). I think we have the same models of each instrument. As an aside your voice volume varies quite a bit and would benefit from some normalization. Thank you for the video!
@justovision X/Y on the scope is in the video about Schmitt triggers, demo-ing the hysteresis loop. Sweep on the function Gen will come when I start on filters. Stay tuned!
@@KludgesFromKevinsCave Thanks, I'll check that video out.
Thanks for the remarks about the audio. I was using an audio compressor in 'kdenlive' but owing to a misconfiguration, it wasn't actually compressing. It'll be a few weeks before the problem's fixed - I try to run a 4-6 video backlog - but I'll try to be more careful moving forward. Still learning this video stuff!
Flexing your 60k counts meter, the yellow one looks to be 10k counts. Nice. Cant wait to get a better look at your scope. Edit: only had to watch a little further. I'm a big fan of Rigol.
The yellow meter is one I got when I was in grad school in the 1980's, on a grad-student budget. It still works. The lack of auto-ranging is annoying, but it's fine as a second meter.
Rigol has a lot of bang for the buck. I picked it out because that's the scope I seem to see on half the electronics-hacker RUclips channels I watch, and the other ones I see are all at least twice the price. I've only a few complaints so far, relating to some really weird quantization artifacts. (The values appear to be quantized once in the A/D, and then again going to the screen, with the result that on some scales, there are screen pixels that never light.)
One of these months I want to do a video or three on restoring the Tektronix analog oscilloscope that I picked up at a surplus auction in the 1980s.
Oh, the other night I got curious and watched where the ranges of the meters switch. The old yellow meter is a 20k count meter, but the current ranges go in steps of 100x. The blue meter is indeed 65536 counts.