On 2017-11-25 21:28, John Larkin wrote:> On Sat, 25 Nov 2017 17:28:49 -0800 (PST), tabbypurr@gmail.com wrote: > >> On Saturday, 25 November 2017 00:09:27 UTC, John Larkin wrote: >>> On Fri, 24 Nov 2017 14:06:48 -0800 (PST), Leslie Rhorer >>> <rhorerles@gmail.com> wrote: >>>> On Friday, November 24, 2017 at 3:48:01 PM UTC-6, John Larkin >>>> wrote: >>>>> I don't know of any problems with the original LM324. >>>>> >>>>> Except the ghastly crossover distortion. >>>>> >>>>> And the pitiful slew rate. >>>>> >>>>> And the wimpy drive. >>>>> >>>>> And the horrible stuff that happens if any of the inputs go >>>>> below ground. >>>> >>>> None of which matter in this situation, which is one reason why >>>> your original suggestion is definitely the front runner. I've >>>> ordered a couple of Op Amps, including a 324, from Mouser for >>>> testing. They should arrive Monday. >>> >>> One other quirk: if one of the four opamps rails, it can mess up >>> the other three. Shared current sources. I don't remember just >>> how bad that is. >> >> I love the 324, it's cheap & very useful. Crossover is easily >> avoided. Don't buy Motorola or bias the output. >> >> But I do wish there were even cheaper opamps with even more corners >> cut. There must be plenty of uses for opamps with major >> compromises, eg poor gain. Trouble is things start expensive and >> drop in price, which would make cruder opamps uncompetitive in the >> early days. And who wants to sell an even cheaper chip when they >> can introduce a high ticket one. >> >> >> NT > > The Diodes Inc version of the LM324 is 6.5 cents, Digikey price by > the reel. Under 2 cents per opamp. > > What does Digikey pay? 5 cents? Why does anybody bother to make and > package a quad opamp for 5 cents? >Probably less. You can buy the AS324 for around 4 cents.> When these were new, one cost about as much as a couple of bicycles. > > https://www.dropbox.com/s/9idlgfug24rqxyb/Philbricks.jpg?raw=1 >Oh yeah. And people with a good meter to match tubes or transistors could still make a buck. -- Regards, Joerg http://www.analogconsultants.com/
Need Op Amp for design
Started by ●November 19, 2017
Reply by ●November 26, 20172017-11-26
Reply by ●November 26, 20172017-11-26
On Friday, November 24, 2017 at 5:28:49 PM UTC-5, Leslie Rhorer wrote:> > > > > > Am I wrong? If not, is there a different choice of high input impedance op amp that can withstand up to 25V when power is shut off? > > > > You should buy a battery management IC, some of them handle lots of cells, and this is especially true of Li batteries. There are physics based considerations that dwarf the triviality of the electronics interconnection topology. > > I am using an off-the shelf LiPo battery monitor specifically designed to monitor LiPo batteries during use. These are extremely common in the Radio Control hobby sector, and are readily available at very low cost. Below is an example. The only problem is these are designed to be manually disconnected when not in use. The reed relays work perfectly, but are too large to be able to shrink the design down to a desirable size for a lower power version of the light. The 100W version uses a battery that is nearly 4" x 4" x 12", so a smaller board is not of any value, but I would like to create a few 20W lights with a smaller footprint and less weight. > > https://www.ebay.com/itm/5pcs-Lipo-Alarm-Low-Voltage-1-8S-Battery-Buzzer-RC-Checker-Tester-LED-Indicator/263108054278?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2060353.m2749.l2649Looks like that one is quite popular. One forum convo talked about killing the current draw by opening the GND lead in the off state, all the inputs remain connected. That might be worth exploring.
Reply by ●November 26, 20172017-11-26
On Fri, 24 Nov 2017 08:28:06 -0800, Joerg <news@analogconsultants.com> wrote:>On 2017-11-24 08:18, John Devereux wrote: >> John Larkin <jjlarkin@highlandtechnology.com> writes: >> >>> On Thu, 23 Nov 2017 07:54:57 -0800, Joerg <news@analogconsultants.com> >>> wrote: >>> >>>> On 2017-11-22 22:22, Jasen Betts wrote: >>>>> On 2017-11-21, Joerg <news@analogconsultants.com> wrote: >>>>>> On 2017-11-21 11:35, Winfield Hill wrote: >>>>>>> John Larkin wrote... >>>>>>>> >>>>>>>> The ancient LM324 has PNP input transistors, and the >>>>>>>> safe input voltages can go to +32 irrespective of V+. >>>>>>> >>>>>> >>>>>> The datasheet says "Don't do that" though. Looking at the innards on >>>>>> page 4 it seems you'd hit a diode path to V+: >>>>>> >>>>>> http://www.st.com/content/ccc/resource/technical/document/datasheet/bd/fc/46/43/26/8f/40/7f/CD00001046.pdf/files/CD00001046.pdf/jcr:content/translations/en.CD00001046.pdf >>>>> >>>>> use the TI part. >>>>> >>>>> http://www.ti.com/lit/ds/snosc16d/snosc16d.pdf >>>>> >>>> >>>> For hobby or small runs it's ok. With contract assemblers it can be >>>> dicey. >>> >>> NEVER allow a CM to substitute parts! >> >> Yes, quite, I am amazed that Jeorg allows this to happen actually given >> his previous postings here. (Regarding documentation control, >> certifications, procedures, etc etc). >> > >As I wrote I didn't allow it and neither did my client. The CM folks >took it upon themselves to "cost-optimize". Which is why they had to eat >the cost for an expedited re-run and fast air-shipment. > > >> Also it seems rather unfair on the original manufacturer of the part. As >> soon as someone releases a clone, only hobbyists should then use the >> original? >> > >In this case it isn't a clone and if one knows about it then IMO one >needs to point out the risk. > >The other question in this case is that even for the versions that allow >an unusually high reverse Vbe there is no spec in the datasheets about >the maximum leakage current that will flow, AFAIK. Li-Ion protection is >a pretty serious matter, not something to take lightly.One amp-hour divided by one microampere is a million hours. -- John Larkin Highland Technology, Inc lunatic fringe electronics
Reply by ●November 26, 20172017-11-26
On 2017-11-26 14:08, John Larkin wrote:> On Fri, 24 Nov 2017 08:28:06 -0800, Joerg <news@analogconsultants.com> > wrote: > >> On 2017-11-24 08:18, John Devereux wrote: >>> John Larkin <jjlarkin@highlandtechnology.com> writes: >>> >>>> On Thu, 23 Nov 2017 07:54:57 -0800, Joerg <news@analogconsultants.com> >>>> wrote: >>>> >>>>> On 2017-11-22 22:22, Jasen Betts wrote: >>>>>> On 2017-11-21, Joerg <news@analogconsultants.com> wrote: >>>>>>> On 2017-11-21 11:35, Winfield Hill wrote: >>>>>>>> John Larkin wrote... >>>>>>>>> >>>>>>>>> The ancient LM324 has PNP input transistors, and the >>>>>>>>> safe input voltages can go to +32 irrespective of V+. >>>>>>>> >>>>>>> >>>>>>> The datasheet says "Don't do that" though. Looking at the innards on >>>>>>> page 4 it seems you'd hit a diode path to V+: >>>>>>> >>>>>>> http://www.st.com/content/ccc/resource/technical/document/datasheet/bd/fc/46/43/26/8f/40/7f/CD00001046.pdf/files/CD00001046.pdf/jcr:content/translations/en.CD00001046.pdf >>>>>> >>>>>> use the TI part. >>>>>> >>>>>> http://www.ti.com/lit/ds/snosc16d/snosc16d.pdf >>>>>> >>>>> >>>>> For hobby or small runs it's ok. With contract assemblers it can be >>>>> dicey. >>>> >>>> NEVER allow a CM to substitute parts! >>> >>> Yes, quite, I am amazed that Jeorg allows this to happen actually given >>> his previous postings here. (Regarding documentation control, >>> certifications, procedures, etc etc). >>> >> >> As I wrote I didn't allow it and neither did my client. The CM folks >> took it upon themselves to "cost-optimize". Which is why they had to eat >> the cost for an expedited re-run and fast air-shipment. >> >> >>> Also it seems rather unfair on the original manufacturer of the part. As >>> soon as someone releases a clone, only hobbyists should then use the >>> original? >>> >> >> In this case it isn't a clone and if one knows about it then IMO one >> needs to point out the risk. >> >> The other question in this case is that even for the versions that allow >> an unusually high reverse Vbe there is no spec in the datasheets about >> the maximum leakage current that will flow, AFAIK. Li-Ion protection is >> a pretty serious matter, not something to take lightly. > > One amp-hour divided by one microampere is a million hours. >Leslie was looking for nanoamps, no idea why. Even a few tens of uA should be ok with 18650 and similar cells. Milliamps, not so much. Had my comeuppance there with bicycle lights where a standby LED is always lit. Silly design and draws 5-10mA. When I used the road bike for several weeks and then wanted to ride my mountain bike I hopped on, click, no lights. I don't know what a LM324 draws with the input 25V or so above V+. She could find out. If it was my projects I'd first look for complete battery management ICs with ship mode or similar low power modes. Less space, less parts, approved design, cheap, no hassle. -- Regards, Joerg http://www.analogconsultants.com/
