[Q] Transistor question - Page 1
Forum section: electronics / beginners

author: itvend
author_rank: Contributor
timestamp: May 02, 2014, 11:46:17 am
content: Hy.So i have little circuit and why does collector output signal does this, it goes 60us longer before dropping to 0V.

author: Andy Watson
author_rank: Super Contributor
timestamp: May 02, 2014, 11:59:30 am
content: You need to take care about where the scope trigger occurs - at the moment you appear to be looking at each signal independently - i.e. the time is not correlated.

author: c4757p
author_rank: Super Contributor
timestamp: May 02, 2014, 12:02:09 pm
content: Andy's right, the signals aren't correlated. But you're also right, the timing is off - but it's actually taking too long to rise back to 12V, not drop down to 0V.You're likely seeing the transistor'sstorage timeor storage delay. When the transistor saturates, you store excess charge onto the base; this charge must be removed (slowly) to switch off.Try aBaker clampto hold the transistor right on the threshold of saturation:Edit - er, or not. Your input waveform is asymmetric too, and the time is perhaps a bit too long to be storage time.Something to keep in mind, anyway.

author: Bored@Work
author_rank: Super Contributor
timestamp: May 02, 2014, 12:28:34 pm
content: Quote from: Andy Watson on May 02, 2014, 11:59:30 amAnd what he missed when "aligning" the waveforms is that the transistor stage inverts. The input has shorter on than off times, so the output has shorter off than on times.

author: itvend
author_rank: Contributor
timestamp: May 02, 2014, 12:49:51 pm
content: Thanks guy-s for good infonow its with correct triggers

author: vk6zgo
author_rank: Super Contributor
timestamp: May 02, 2014, 10:39:33 pm
content: Quote from: Bored@Work on May 02, 2014, 12:28:34 pmAnd it took a grumpy old Greybeard to notice!

author: David Hess
author_rank: Super Contributor
timestamp: May 03, 2014, 01:24:27 pm
content: What make and model of DSO like that supports independent triggering?I am used to seeing that kind of mistake on analog oscilloscopes which support alternate triggering.

author: free_electron
author_rank: Super Contributor
timestamp: May 03, 2014, 03:56:59 pm
content: What piece of shit scope allows moving one trace in respect to another ? (Apart from probe skew alignment of course)I have growled multiple times at scopes that cannot time-lock traces. Example : throw something in memory, then tap a live signal, hit single shot or stop, start scrolling , the memory traces stay , only the live ones scroll... Totally useless if you want to do a comparision between an earlier captured signal and what you just captured. Timelock is broken. All visible traces should scroll in sync when operations on timebase or trigger position are done post-capture.Of course the scope input stage must allow for skew between channels to compensate cable and probe length , but that compensation happens BEFORE viewport manipulations.

author: David Hess
author_rank: Super Contributor
timestamp: May 03, 2014, 04:13:53 pm
content: Quote from: free_electron on May 03, 2014, 03:56:59 pmSome allow a trace to be "unlocked" so they may be shifted horizontally relative to the others.A more common problem at least with analog oscilloscopes is alternate triggering while in alternate instead of chop mode which destroys the displayed phase relationship between traces. It is doubly annoying when a DSO does it. The solution is to force the trigger to only use one channel or to use chop mode.QuoteI agree that it should happen first but probe skew is usually an insignificant source of error on slow oscilloscopes. I have only seen it compensated for significantly above 100 MHz and never as part of the horizontal positioning except in very special circumstances like when using a current probe or active probe.