You just need one resistor from the pos. rail to the output (it'd take a pretty crappy offset to be greater than about half the output Vcesat). With this you can even balance the divider's current and avoid the opamp some dissipation.
-- Thanks, Fred.
Quite a bit noisier though, just due to the high operating temperature.
Germ of a nice idea though...it ought to be possible to make a hybrid reference, e.g. with a high power, quiet reference that gets fired up periodically to adjust the voltage on a hold cap. You could even correct for the kT/C noise, and all at really low power.
Cheers,
Phil Hobbs
The R4-5 divider needn't source much current--just enough to overwhelm the op amp's bias current, whereas the one-resistor pullup needs to provide a little more juice to dominate the op-amp's output stage, I suspect, depending on the op amp... but I like it.
Simple, clever. Nice touch.
Cheers, James Arthur
Until you get the next production lot and the guy from final QC comes down the hallway, flailing and hollering and all that.
Plus Digikey doesn't have any. Not a good sign ....
[...]-- Regards, Joerg http://www.analogconsultants.com
He was probably thinking about all the paperwork he'd have to do if he fell, and lived. Destruction of government property creates lots of extra work. :(
-- Service to my country? Been there, Done that, and I\'ve got my DD214 to prove it. Member of DAV #85. Michael A. Terrell Central Florida
If you need super performance you gotta tune each one Joerg, of course. Or buy an IC with a buried zener in it.
Digikey?
Grins, James Arthur
I'd vote for the IC then ;-)
Yeah, my house rule here is that when Digikey doesn't carry something or is constantly out of stock on it then it's a boutique part. And boutique parts usually turn into sleepless nights, overtime, cancelled vacation trips and all that.
:-)))
-- Regards, Joerg http://www.analogconsultants.com
Fine, if you're an IC designer and can control the properties of your 100uA device. My point was that 1% zener diodes are basically a waste, unless their 1% voltage and tempco specs are specified at a sensible current, rather than the usual 20mA. I think that's why they didn't succeed as a product. On the other hand, voltage-reference ICs with 1% or better- specs certainly did succeed. At least in my designs. And, they ran at sensible currents.
If you used a reverse-BE junction and well-controlled its characteristics, that's great, because the tempco could have been lower than the usual Vbe-reference device. One of the things I liked about the venerable 723 regulator IC was its nice quiet zener diode.
Exactly. Plus most of the "low current zeners" are just the same old soup, regular zeners measured in the knee. I had lengthy discussions with mfgs about delivering real low current zeners after a client had a major line stop situation where a low current zener drifted out of spec after the umpteenth reel. The result? More of those "measured in the knee" varieties. So I designed in the TLV431. No more zeners there. Meaning they lost a business they could have had.
Why don't they make smaller geometry zeners? It can't be rocket science and the profits from each wafer should greatly increase.
-- Regards, Joerg http://www.analogconsultants.com
Seems like an awful lot of paperwork for a thing where you could have just said, "No, thanks." ;-)
Cheers! Rich
It is at the top of the second page of the data sheet.
-- Bill Sloman, Nijmegen
Someone published a short paper in the (British) Journal of Scientific Instruments some forty years ago on using the forward-biased collector base diode of a 2N2639 gold-doped switching transistor
http://www.ortodoxism.ro/datasheets/fairchild/MMBT2369A.pdf
to compensate the the tempeature coefficient of the reversed biased base-emitter diode.
Because both diodes were at the same place in the same package, the temperature compensation could be pretty good, and the paper went on to tell you how to tune the current through the part (at around 2mA) to minimise the temperature coefficient of the part as a whole - you produced a temperature excursion in the part by prodding it with a hot soldering iron and monitored the voltage drop across the part with a six-digit digital voltmeter ...
A really neat trick, but one that I've never tried to use.
-- Bill Sloman, Nijmegen
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