Measure twice, cut once, and count carefully... - Page 1
Forum section: electronics / general

author: c4757p
author_rank: Super Contributor
timestamp: December 07, 2013, 01:34:54 am
content: I spenthourstoday trying to tame a flyback converter that I had already carefully verified at least had a chance of stability.Turns out I overwound the transformer after losing count and just "eyeballing" it - new cores, not familiar with them, no ability to eyeball them...... the secondary inductance was too high by a factor of about 80 (that's right, I seriously overwound by a factor of 9, and no, I don't know when I became so stupid). Then, when I measured the transformer, I failed to notice that the LCR bridge was two ranges up, and read an error factor of 0.8 (acceptable). The control loop did not like this atall.After all the time I spent dicking around with the compensation network, the solution was as simple as spreading the core gap a bit more. Didn't even have to rewind, I just inserted a couple paper spacers. And the result was so stable it didn't even need any compensation network at all.Folks, measure carefully!

author: Fsck
author_rank: Super Contributor
timestamp: December 07, 2013, 01:39:40 am
content: how do you overwind by 9x?

author: c4757p
author_rank: Super Contributor
timestamp: December 07, 2013, 01:40:30 am
content: Quote from: Fsck on December 07, 2013, 01:39:40 amI was watching the news, drinking coffee and talking

author: deth502
author_rank: Frequent Contributor
timestamp: December 07, 2013, 01:57:06 am
content: you think thats bad, i spent 2-3 hrs the other day trying to figure out why my very simple lm358 amplifier circuit wasnt working and i couldnt get any kind of signal off a microphone.after rewiring and double checking everything about 50 times, i realized i was wiring it to a 555, not an lm358.

author: xrunner
author_rank: Super Contributor
timestamp: December 07, 2013, 01:59:36 am
content: Quote from: c4757p on December 07, 2013, 01:34:54 amDude, per the audiophile thread ...It's the Nanoparticles. You left out the Nanoparticles!

author: vk6zgo
author_rank: Super Contributor
timestamp: December 07, 2013, 04:01:23 am
content: Quote from: deth502 on December 07, 2013, 01:57:06 amLadies & Gentlemen,we have a winner!!

author: Six_Shooter
author_rank: Regular Contributor
timestamp: December 07, 2013, 02:42:11 pm
content: Quote from: deth502 on December 07, 2013, 01:57:06 amThis made me LOL for real.I'm not laughing at you, I'm laughing with you, because I've done similar things...

author: brabus
author_rank: Frequent Contributor
timestamp: December 07, 2013, 03:17:57 pm
content: I HATE L79xx linear regulators in TO220 package.Classic scenario:BANG! Uh-oh, maybe I shorted something.RE-BANG! Uh-oh, but this time I have no load!TRI-BANG! WTF, pinout is not Input-GND-Output! L79xx, you got me again!

author: c4757p
author_rank: Super Contributor
timestamp: December 07, 2013, 03:20:31 pm
content: Easy way to remember that ground isn't in the middle: the substrate often has the most negative voltage. That's the input, for a negative regulator.This obviously doesn't work for everything - LM317 for instance - but it is something to keep in mind. Itdoeswork for LM317 if you consider that the output is the most negativerail(ADJ is just signal, not power, as most of the quiescent current goes through the output).

author: SeanB
author_rank: Super Contributor
timestamp: December 07, 2013, 06:52:07 pm
content: You can wire a 555 to act as an amplifier though, not exactly hifi but something that amplifies somewhat.

author: brabus
author_rank: Frequent Contributor
timestamp: December 07, 2013, 11:09:54 pm
content: Quote from: c4757p on December 07, 2013, 03:20:31 pmVery interesting, thank you!Sorry but I am not so much into microelectronics, I work with components that I can see with naked eye (although 01005s beginto be a bit nasty in this sense). But I always like to learn.I go ahead just with sensible thought: the substrate is always kept at the most negative voltage to avoid direct conduction of bulk diodes, am I right?Is this the main reason or is there something else?Thanks again!About working with negative voltage, please stand up if you reversed the classic electrolytic! Come on, I know we all did!

author: c4757p
author_rank: Super Contributor
timestamp: December 07, 2013, 11:20:46 pm
content: Quote from: brabus on December 07, 2013, 11:09:54 pmBasically. As far as I know, the substrate sits at the most negative voltage because the simplest way to build an N-channel FET or NPN transistor places the source/collector on the bottom, directly over the substrate. And then, yes, you do have to prevent the bulk diodes from conducting. (Keep in mind, I'm hardly a semiconductors expert either, but it is a trend that is easy to see.)

author: mrflibble
author_rank: Super Contributor
timestamp: December 08, 2013, 04:10:02 pm
content: Quote from: Six_Shooter on December 07, 2013, 02:42:11 pmIndeed.Things like swapping the positive and negative supply on an opamp, that's always fun! Hey, it is sortof doing what it should be but ... gee that looks weird.

author: JoannaK
author_rank: Frequent Contributor
timestamp: December 08, 2013, 06:55:07 pm
content: Quote from: c4757p on December 07, 2013, 11:20:46 pmWell, those things seen to happen, for people who work with electronics. Years back I remember once noticing that my Pic based thingy suddenly didn't need any battery to operate.Cause: I had it connected it to my PC serial port with my own hodgepodge level converter. Can't recommend powering any microcontroller via IO pin, but it's definitely possible (at least with 16C84)..