Back to Basics video: Transistor bias circuits and Beta dependence - Page 1
Forum section: electronics / beginners

author: w2aew
author_rank: Super Contributor
timestamp: December 02, 2014, 12:08:38 pm
content: This back to basics video describes a few methods to setup the bias level (or quiescent point, Q-point) of a bipolar transistor, and looks at how the q-point is affected by the transistor's current gain (Beta).

author: void_error
author_rank: Frequent Contributor
timestamp: December 02, 2014, 02:39:19 pm
content: Nice videoIt would be awesome if you also made one for low-power MOSFETs, haven't seen many linear applications for them and I'm curious how well they'd work, stuff like 2N7002 and similar.

author: dentaku
author_rank: Frequent Contributor
timestamp: December 03, 2014, 03:38:34 pm
content: That's all fine but it would be nice for beginners to show why that's useful.What's the simplest use of such a thing and what happens when it's not done correctly?

author: w2aew
author_rank: Super Contributor
timestamp: December 03, 2014, 11:57:01 pm
content: Quote from: dentaku on December 03, 2014, 03:38:34 pmBottom line- it is bad practice to design a circuit that is dependent upon a the Beta (hfe) of a transistor. This is because this parameter is NOT well controlled, and can vary by quite a lot. The three transistors used in this video were all PN2222A from the same manufacturer. The point of the video is that when designing a circuit, it's best to design it so that the bias point, performance, operation, etc. of the circuit is NOT highly dependent upon Beta.

author: c4757p
author_rank: Super Contributor
timestamp: December 04, 2014, 12:26:08 am
content: Quote from: dentaku on December 03, 2014, 03:38:34 pmThat's what the whole video wasabout!

author: dannyf
author_rank: Super Contributor
timestamp: December 04, 2014, 01:22:59 am
content: QuoteFor DC applications, they are identical to bjt (npn in this case). And if you design carefully, the Vgs vs. Vbe differences can be ignored.QuoteAny circuit designed with a bjt will be dependent on its beta. The goal is to design it in such a way so that the variations due to beta differences don't materially impact the performance of the circuits.

author: Syntax_Error
author_rank: Regular Contributor
timestamp: December 04, 2014, 02:18:19 am
content: That's what he meant. It is clearly articulated in the video. As a newb myself, I had zero trouble understanding the topic covered.W2AEW, thanks for another great video.I really like the combination of schematics and diagrams, breadboarding, dialog, instrument screen details, RF doohickey usage, and how you tie together the theory behind the topic to the real world observations you show in your videos.Your videos on IQ modulation were great, too. Just wanted to say thanks and a job very well done.

author: frostheave
author_rank: Contributor
timestamp: December 04, 2014, 02:31:16 am
content: Fantastic video. Can't wait for the next in the series! Thanks a lot w2aew.

author: w2aew
author_rank: Super Contributor
timestamp: December 04, 2014, 02:38:31 am
content: Thanks for all the great comments, guys! It's feedback like this that inspires me to keep producing more videos. Too bad my full time job and normal private life only give me barely enough time to do one video per week or so.I'm always open to suggestions too - so feel free to let me know what topics you'd like to see, and I'll add them to my (long) list of "to-do's"

author: rozeh
author_rank: Regular Contributor
timestamp: December 04, 2014, 06:28:28 am
content: Thanks w2aewQuote from: void_error on December 02, 2014, 02:39:19 pm+1 for brilliant suggestion!a video with these contents could be much more helpful and useful:1- Introduction to all type of FETs and MOSFETs2- How they work and what is the difference between them?3- How to bias them as a switch or for amplifying a signal?Nowadays, the MOSFETs are so much popular.

author: dentaku
author_rank: Frequent Contributor
timestamp: December 04, 2014, 05:57:20 pm
content: Like I said, the video was fine. It demonstrated what Alan set out to show.What I like about most W2AEW videos is how well Alan can demonstrate something simply once he moves over to the oscilloscope.I guess this latest video goes well as an addition to this older video.

author: aroby
author_rank: Regular Contributor
timestamp: December 04, 2014, 06:21:42 pm
content: Quote from: w2aew on December 04, 2014, 02:38:31 amIs there somewhere, other than the videos, where your diagrams can be viewed? Even having a steady shot of the diagram at the end of a video would be helpful.Great stuffAnthony

author: dentaku
author_rank: Frequent Contributor
timestamp: December 04, 2014, 11:05:14 pm
content: Quote from: aroby on December 04, 2014, 06:21:42 pmThat's a good idea. A few times I've taken screenshots of the video when there where no hands in the shot so I could later build them in a simulator.

author: Radio Tech
author_rank: Frequent Contributor
timestamp: December 05, 2014, 01:14:42 am
content: Quote from: w2aew on December 04, 2014, 02:38:31 amYou cannot stop life, so quit work and come a full time video bloggerQuote from: dentaku on December 04, 2014, 11:05:14 pm+3 on that. A few plain shots taken at the end would put his videos over the top.Alan has some of the greatest video's and I enjoy watchin them. Very easy to follow and understand.

author: w2aew
author_rank: Super Contributor
timestamp: December 05, 2014, 04:32:51 am
content: It just so happens that I scanned the notes for about 30 of my videos, and placed links in the YouTube video notes where you download the pdf files. This video is one of the ones that I scanned, so revisit the video in YouTube and check out the video notes.

author: aroby
author_rank: Regular Contributor
timestamp: December 11, 2014, 08:21:27 pm
content: Quote from: w2aew on December 05, 2014, 04:32:51 amExcellent, thanks!

author: dentaku
author_rank: Frequent Contributor
timestamp: December 11, 2014, 10:24:57 pm
content: Quote from: w2aew on December 05, 2014, 04:32:51 amThat's good to know. Youtube hides that stuff under a little link that says "SHOW MORE" so I never noticed it.

author: chickenHeadKnob
author_rank: Super Contributor
timestamp: December 11, 2014, 11:09:26 pm
content: Quote from: w2aew on December 04, 2014, 02:38:31 amHere is a suggestion that should be right up your alley: super regenerative receivers. a whole show on how they work, with a bit of history.if you already have covered this and I missed it I apologize. I have largely learned electronics through self-teaching so I have many gaps in knowledge in both RF and basic analog. I think I know how super-regeneration works but would appreciate the confirmation you could give.

author: w2aew
author_rank: Super Contributor
timestamp: December 12, 2014, 12:57:37 am
content: Quote from: chickenHeadKnob on December 11, 2014, 11:09:26 pmYeah, regen receivers have been on my to-do list for a long time. I hope to get around to it sometime this winter.