Are TS555's really supposed to suck this much?
in [Design]
|
Prev: ZXSC400 LED driver problem
Next: calculate MTBF
From: Tim Williams on 22 Jan 2010 01:11 "John Fields" <jfields(a)austininstruments.com> wrote in message news:7t5hl5lbis9m3talpgj3140v73nbk2nhhn(a)4ax.com... >>Well, duh, it's a 555. > > It's like Invasion of the Body Snatchers, where a Sloman pod was placed > next to Larkin while he was asleep... ;) Meh, I rarely use 555s either. I prefer LM393s for such purposes -- more general, though the parts count usually ends up a lot higher. When you're packing parts on perfboard and folding up your resistors, it doesn't really matter. In fact, one of the few places I actually used a 555 was the HV generator, http://webpages.charter.net/dawill/Images/High%20Voltage%20Supply.gif where the *bipolar* chip's ample output current makes a good starting point for driving bigger transistors (hmm, those 1k's don't look very impressive though). Works a lot better than those shitty 2N3055 drivers plastering the internet. As for this thread, my excuse: it's a school project, so it has certain requirements, like simplicity and "has to look nice to the guy who's grading it" (what could be better than a million 555's?). That, and it was late at night after a meeting, and you know how useful meetings are. ;-) Tim -- Deep Friar: a very philosophical monk. Website: http://webpages.charter.net/dawill/tmoranwms
From: Archimedes' Lever on 22 Jan 2010 08:20 On Fri, 22 Jan 2010 04:14:42 -0800 (PST), Bill Sloman <bill.sloman(a)ieee.org> wrote: > >Archimedes Lever, you really don't have a clue about electronic >design, and you illustrate the point by slagging off people who do. Is that what you are calling yourself?
From: Jim Thompson on 22 Jan 2010 09:42 On Thu, 21 Jan 2010 21:49:59 -0800, John Larkin <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: [snip] > >I used a 555 once in my life, to run a little charge pump to make some >negative voltage from +12. I ran the output back to the timing cap >through one resistor, avoiding the usual extra parts in the >charge/discharge path to get a square wave... something that I thought >was obvious but not on the datasheet. I still don't see that >configuration very often. > >John You've seen it many times from me. But it gives 50% ONLY with the CMOS version. ...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 | I love to cook with wine. Sometimes I even put it in the food.
From: John Fields on 22 Jan 2010 12:50 >I used a 555 once in my life, to run a little charge pump to make some >negative voltage from +12. I ran the output back to the timing cap >through one resistor, avoiding the usual extra parts in the >charge/discharge path to get a square wave... something that I thought >was obvious but not on the datasheet. I still don't see that >configuration very often. --- It's fairly common, and Maxim shows it on page 6 of their 17 year old CMOS 555 data sheet at: http://datasheets.maxim-ic.com/en/ds/ICM7555-ICM7556.pdf It's not so common with bipolar 555s because its output doesn't swing symmetrically about Vcc and GND, so it's not easy to get a square wave out of it. Plus, its output doesn't swing to the positive rail, so if Vcc gets low enough, the output won't swing high enough to get to 2Vcc/3, THRESHOLD will never be triggered, and the timing cap will never discharge. JF
From: Gerhard on 22 Jan 2010 17:41
"Bill Sloman" <bill.sloman(a)ieee.org> wrote in message news:6f8f419d-feee-4396-aab4-4d3d26e0d253(a)22g2000yqr.googlegroups.com... On Jan 22, 2:26 am, Archimedes' Lever <OneBigLe...(a)InfiniteSeries.Org> wrote: > On Thu, 21 Jan 2010 16:15:53 -0800 (PST), Bill Sloman > > <bill.slo...(a)ieee.org> wrote: > >On Jan 21, 7:09 pm, John Fields <jfie...(a)austininstruments.com> wrote: > >> On Wed, 20 Jan 2010 21:18:43 -0800, John Larkin Snip . . . . > >It's more that John Larkin is good at electronic design, and has > >recognised precisely how useful the 555 is - which is to say, not a > >useful device in most applications. > > Why then is it STILL one of the most widely used chips in existence? >Legacy design. It worked for specifc applications, back in 1971 when > Hans Camenzind designed it, and people have been copying these > circuits ever since. Not because there isn't a better alternative - > there almost always is - but because finding out what the better > alternative is, qualifying the new component and explaining to the > boss why you've wasted your time solving a non-problem all take time, > and while the time is usually well-spent, in the long term, lots of > people have more immediate short-term concerns. Snip some more .... Hans R Camenzind has some interesting information on IC design for those that would like to try their hand at it. Search for the article "Redesigning the old 555" by Hans Camenzind. It was published in the IEEE Spectrum Volume 34 Issue 9, Sept. 1997. IEEE Explore has a copy of the article. http://ieeexplore.ieee.org/iel3/6/13487/00619384.pdf?arnumber=619384 Google might have a link to a free copy of the IEEE Spectrum article. A short article on Hans Camenzind and the 555 design history is available at http://www.eetimes.com/special/special_issues/millennium/milestones/camenzind.html The text and audio recordings of an interview with Hans on the design of the 555 and PLLs are available at http://semiconductormuseum.com/Transistors/LectureHall/Camenzind/Camenzind_Index.htm It covers most of the info in the IEEE Spectrum article. There are however more detail and diagrams on the 555 design in the IEEE article. I consider my self lucky to have experienced the days of BIG IC mask drawings and peeling Rubylift. Enjoy the weekend Gerhard van den Berg CSIR |