Hey there - is there such a thing as a 1% zener diode? They all seem to be about 5%. I was looking to make a 10V vref and the best I was able to find was the Digi-Key EDZTE6110BCT-ND, which is accurate to
2.3%. This just strikes me as odd - and makes me wonder if I'm looking in the wrong place or something.I did, however, discover that there are actual 10V vref chips out there - so I'm planning on going with one of those.
-Michael
You're assuming that these devices start to conduct at 10.00V sharp ? This is not the case anyway. The specified conduction voltage is defined at 1mA.
And yes, a 10V reference is a different device.
Rene
-- Ing.Buero R.Tschaggelar - http://www.ibrtses.com & commercial newsgroups - http://www.talkto.net
On a sunny day (Tue, 24 Jul 2007 06:10:10 -0700) it happened Michael wrote in :
Zener diodes are actually in a breakdown region.. so unreliable, not accurate etc by nature.
10V reference? A LM317 with 2 resistors or a 10 turn poti will make any reference you like, for less money with better temp stability, then a zener, possibly for less money too. All that with more power....
Well, my knowledge of them was that you would always put a resistor inline with them to give it a proper bias current so that you would hit the exact right voltage. I need the 10V to connect to the non- inverting input of an Op-amp (OP747). Thus I'm not worried about a current drain on the line.
-Michael
No. Zener diodes are mass-produced and sorted into 10% and 5% bins, but if you require 1% accuracy you need a laser-trimmed resistor (at least) in addition to bias current regulation and other niceties. 10V 1% references are trimmed ICs, not discrete zeners.
REF-01 is a typical such part; see
Even if 1% tolerance did exist, I think the thermal drift (due to self heating and a range of ambient temperatures) would make the 1% pointless. D from BC
TL431 ??
...Jim Thompson
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| James E.Thompson, P.E. | mens |
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The 10V reference chip is a better choice, but I once had a set of precision zeners at either 1 or 2% increments, IIRC.
Once upon a time zeners were king as reference diodes. The 1n829a, for example: 6.2V, 5ppm/C.
Cheers, James Arthur
Only at 7.5mA - to get all the precision that you paid for with the ! N829, your needed a precision resistor biased from the reference voltage to keep the current stable at just the right value. See
http://www.ortodoxism.ro/datasheets/motorola/1N823.pdf
and note that the temperature stability is specified at 7.5mA
+/-0.01mA - the better the diode the closer you've got to hold the current to 7.5mA to maintain that stability.-- Bill Sloman, Nijmegen
In general, zeners make piss poor regulators.
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Precision voltage reference zeners are pretty much a thing of the past. You were limited to a certain voltage (around 6.2V) and forward current (quite a few mA, IIRC) to get zero (nominal) tempco-- as determined by the physics. ICs are much better for most applications requiring much accuracy, and are reasonably priced.
The LM4040 is an inexpensive shunt (two active pins, just like a zener) reference that might do your job, and it's available in 10V with tolerancces of 2%, 1%, 0.5%, 0.2% and 0.1%, and spec'd at 150uA. Tempco is nothing special (100 or 150ppm/K for all tolerances, but still far better than what you'd get with an uncompensated 10V zener.
Of course if you can use a series reference that might save you a part, but they tend to be a bit more expensive.
Best regards, Spehro Pefhany
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In them days I preferred the uA723 when I needed precision. Sometimes I still do that :-)
-- Regards, Joerg http://www.analogconsultants.com
At Cambridge Instruments, twenty years ago, we liked the Linear Technology voltage references
http://www.ortodoxism.ro/datasheets/lineartechnology/1019fcs.pdf
5ppm/C and available with tight tolerances. Farnell doesn't seem to stock the 10.00V part, but does have the 5.00V voltage part for about $15 each in small quantities.When I last looked, Thaler could do better, but their parts were appreciably more expensive.
-- Bill Sloman, Nijmegen
I found the 723 seem to have a lot of failed units out there for what ever reason? THey just seem to fail and go into full output.. that's not very good if you don't have crowbar protection.
-- "I\'m never wrong, once i thought i was, but was mistaken" Real Programmers Do things like this. http://webpages.charter.net/jamie_5
I usually do have a crowbar but I have never seen that phenomenon, and it's been decades. What happened a lot in my teenage days was that chips showed up from "re-labelers" and other shady sources, often at regular electronics stores. Never seen a uA723 from there but I did end up with a batch of uA741 that were totally out of spec. This is very frustrating for a teenager who isn't a chip expert yet.
The 723 is alive and kicking, and very reliable. Look at any linear brick supply from Condor or PowerOne. I just bought a few for a prototype and sure enough they still use the good old 723. By default they usually have a crowbar but not so much out of concern for the 723, it's to protect against a pass transistor that shorts out.
-- Regards, Joerg http://www.analogconsultants.com
I once read somewhere that you could put an ordinary forward-biased silicon diode in series with a zener and their tempcos would tend to cancel out, albeit they didn't say how well. :-)
Cheers! Rich
The only 723 failures I can recall resulted in low or no output. I've only seen a few bad ones, but loads of them in equipment and modular power supplies.
i agree about the crowbar. Anyone who builds that type of supply needs OVP.
-- 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
I also have a set of 1% zener diodes, but for real-world use they're nearly useless, because they have to be used at the exact specified test current. That's why I still have 'em, never found a good way to use them!
Use the zener to reference an OpAmp style current mirror when sources current to the zener.
The "magic" is in how to get it to start ;-)
I built a chip long ago which did that using the E-B junction as the zener. Not for much accuracy, but for significant PSRR in the bias system.
...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC\'s and Discrete Systems | manus |
| Phoenix, Arizona Voice:(480)460-2350 | |
| E-mail Address at Website Fax:(480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |
America: Land of the Free, Because of the Brave
That is an IC full of transistors. D from BC
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