feedback and stability
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From: JosephKK on 3 Jan 2010 21:34 On Fri, 01 Jan 2010 16:16:03 -0700, Jim Thompson <To-Email-Use-The-Envelope-Icon(a)My-Web-Site.com/Snicker> wrote: >On Fri, 01 Jan 2010 14:00:13 -0800, >"JosephKK"<quiettechblue(a)yahoo.com> wrote: > >>On Tue, 29 Dec 2009 08:50:37 -0700, Jim Thompson <To-Email-Use-The-Envelope-Icon(a)My-Web-Site.com/Snicker> wrote: >> >>>On Mon, 28 Dec 2009 18:36:07 -0800, >>>"JosephKK"<quiettechblue(a)yahoo.com> wrote: >>> >>>>On Mon, 28 Dec 2009 18:57:06 -0500, ehsjr <ehsjr(a)nospamverizon.net> wrote: >>>> >>>>>JosephKK wrote: >>>>>> On Thu, 24 Dec 2009 14:52:20 -0500, ehsjr <ehsjr(a)nospamverizon.net> wrote: >>>>>> >>>>>> >>>>>>>Jim Thompson wrote: >>>>> >>>>><snip> >>>>> >>>>>>>> >>>>>>>>TL431's don't SWITCH. They're more akin to an OpAmp. >>>>>>> >>>>>>>Strictly speaking, no, but for usage here, it's simplest to >>>>>>>think of them switching. The switching is like what you see >>>>>>>on a typical zener curve where V goes from sloped to flat >>>>>>>when the zener avalanches and conducts in the reverse >>>>>>>direction. So they can be thought of as on or off. >>>>>>> >>>>>> >>>>>> >>>>>> EUWWW. According to the datasheet is supposed to be used as a >>>>>> linear (read non-switching) device. >>>>> >>>>> From the datasheet: >>>>>"Active output circuitry provides a very sharp turn-on >>>>>characteristic making these devices excellent replacements >>>>>for Zener diodes..." >>>>> >>>>>Where do you see the datasheet indicating it "is supposed to >>>>>be used as a linear (read non-switching) device" ? >>>>>How do you define linear as non-switching? >>>>> >>>>>I'm sure you have something in mind here, but I'm not >>>>>getting it. Vin vs Vout is anything but linear when the >>>>>device is turned on. So you must have something different >>>>>in mind. As to switching, the datasheet specifies a >>>>>very sharp turn-on and refers to a zener. How does my >>>>>description of that fail to capture the gist? >>>>> >>>>>Ed >>>>> >>>>>> >>>>>> >>>>>>>Ed >>>>>>> >>>>>>> >>>>>>>>To do it correctly you want a FIXED FREQUENCY oscillator with variable >>>>>>>>duty cycle. Have the TL431 vary the duty cycle. >>>>>>>> >>>>>>>> ...Jim Thompson >>>> >>>>I thought i read something like walking back and forth around the >>>>knee of the regulation curve. Did i? >>> >>>What "knee"? TL431's are quite sharp. Treat it as an OpAmp... >>>drawing showing how sometime today. >>> >>> ...Jim Thompson >> >>Please reread my question. Please answer it. Did or did not someone >>discuss wobbling it around the corner of the knee? > >Maybe you did. I don't remember it. It's dumb. That sort of >"solution" doesn't stick in my brain ;-) > > ...Jim Thompson Not much of answer, but it will do. You just heard it from JT, regulating by wobbling around the zener knee is dumb.
From: Jim Thompson on 3 Jan 2010 22:10
On Sun, 03 Jan 2010 18:34:12 -0800, "JosephKK"<quiettechblue(a)yahoo.com> wrote: >On Fri, 01 Jan 2010 16:16:03 -0700, Jim Thompson <To-Email-Use-The-Envelope-Icon(a)My-Web-Site.com/Snicker> wrote: > >>On Fri, 01 Jan 2010 14:00:13 -0800, >>"JosephKK"<quiettechblue(a)yahoo.com> wrote: >> >>>On Tue, 29 Dec 2009 08:50:37 -0700, Jim Thompson <To-Email-Use-The-Envelope-Icon(a)My-Web-Site.com/Snicker> wrote: >>> >>>>On Mon, 28 Dec 2009 18:36:07 -0800, >>>>"JosephKK"<quiettechblue(a)yahoo.com> wrote: >>>> [snip] >>>>> >>>>>I thought i read something like walking back and forth around the >>>>>knee of the regulation curve. Did i? >>>> >>>>What "knee"? TL431's are quite sharp. Treat it as an OpAmp... >>>>drawing showing how sometime today. >>>> >>>> ...Jim Thompson >>> >>>Please reread my question. Please answer it. Did or did not someone >>>discuss wobbling it around the corner of the knee? >> >>Maybe you did. I don't remember it. It's dumb. That sort of >>"solution" doesn't stick in my brain ;-) >> >> ...Jim Thompson > >Not much of answer, but it will do. >You just heard it from JT, regulating by wobbling around the zener knee is dumb. Yep, it's dumb. Wobbling is definitely DUMB! ...Jim Thompson -- | James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | If I'm talking, you should be taking notes. |