Hello Warren, many thanks for your valuable response.
If you want to make something in volume
The planned number of devices is more in the range of 2 up to four.
I guess that the others are a LM399 or a LTZ1000 based solution (both with heaters).one of only a very few possible solutions.
Thats a good hint otherwise I will get the humidity changes of the PCB as stress on the device.Don't just solder the parts down on a PCB without a stress relieve loop in the leads.
Do you have typical values over a 64-90 °F range. Will it be above 1ppm/K or below?The zero TC current can be set so that the voltage at most any two temperatures will be the same. (<< 1PPM)
From your plot it would be 0.33ppm per 3 degrees in narrow range i.e. 0.1
ppm per degree. By the way: is it degrees Fahrenheit or degrees Celsius (= 3 Kelvin)?
From a given batch, any that are considerable different, I don't use becauseThats interesting since I have 5 pieces of the brand new LT1236AILS-5 devices.they may have something else wrong going on.
4 of them have a tempco of 2-3 ppm/K around room temperature. 1 piece has a very flat tempco of around 0.2ppm/K (picture attached) If I understand you right then you would not use this device because it does behave other than the others?On the other side it seems to be the device with the largest ageing rate of the 5 pieces.
One experience that I did is that devices out of one batch which have a low tempco
around room temperature tend to have a larger hysteresis and vice versa. So I still hope that anyone has experiences with hysteresis of the zeners. With best regards Andreas----- Original Message ----- From: "WarrenS" <[email protected]>
To: <[email protected]> Sent: Saturday, January 26, 2013 9:48 PM Subject: Re: [volt-nuts] Some questions to zeners (1N823-1N829)
Andreas If you want to make something in volume which is just pretty good, I would not recommend this method for a new design. On the other hand, if this is a nuts thing to make the very best, this is one of only a very few possible solutions. Here are some general answers, most of my experience with these parts is pretty dated, (i.e long ago). As when pushing the performance limit of any reference, there is a lot of variation between parts and even more so between manufactures. Solution is, select, Age, select, test, grade, select.As far as my experience with 1N823, performance depends on the run and whatis left after the manufacture has selected out the others.With 1N823's, Yield can often go to zero. With 1N825's a typical yield I'veseen is around 25-50% (from the right manufacture and batch)Yes the main difference is the zero TC current, with some parts there is nozero TC current. So yes you are more likely to get a lower current TC such as 5 ma from a 1N823 or 1N825 than a 1N829, but it could of course be > than 7.5 ma. I don't use anything that does not have a zero TC between ~ 4 and 10 maI found TC to be very much a Batch thing, with up to 50% of the majority ofa batch, tending to be similar.From a given batch, any that are considerable different, I don't use becausethey may have something else wrong going on.Another thing that needs to be selected for in high end references, and willvary by manufacturer, is 1/F noise. The random jumps in the voltage. For me, hysteresis has not been a issue over room temperature changes for the most part, but something that has to be checked. Some Manufactures are better than others, and hysteresis can and will beeffected by assembly, layout, or anything that puts any stress on the part.Don't just solder the parts down on a PCB without a stress relieve loop in the leads. The zero TC current can be set so that the voltage at most any two temperatures will be the same. (<< 1PPM)If the voltage change in-between those two temperatures is too much, lots ofways to add an additional second order temperature compensation. For the best TC performance, consider the mini-oven idea with the zener, heater resistor, and thermistor all heat shrunk together. With a lot of outer insulation, it could be done low power by adding an addition 0 to 5 ma to the heater resistor. Everything has it's trade offs. The trade off using these zeners is time and complexity. For these parts, 5ma is about as low as you are going to get. For low power, there are many things Much better. The trade off you make to get low power is "Noise" & stability.The trade off you make for the good TC of LM399 is long term stability, PPMnoise, and the high cost of selection fall outs. The best solution will depend on many things including the desired performance, how many you want to make, the cost you place on selection time,and if you can still find the 1N825's at a reasonable price like they wherein the 70s & 80s. (& $0.10 in 2000s) For a xfer standard, the Most important criteria is 1/f random noise. Most everything else can be compensated out. For that, it is hard to build anything better than using a 1N825 selected device. Plot attached. ws ************************************Date: Sat, 26 Jan 2013 16:30:34 +0100 From: "Andreas Jahn" <[email protected]> Subject: [volt-nuts] Some questions to zeners (1N823-1N829) Hello all, Hello Warren, after having experimented a lot with 5V monolithic zener references and still not found the ideal solution I want to try a 1N82x based solution. For me a extended room temperature range of 25 degrees centigrade +/- 7 degrees (64-90 ?F) is of interest. Since I plan to have battery supplied instruments a lower supply current would be of interest. For the zeners a zero TC current is stated. Over which temperature range the TC is nearly zero. How large is the voltage deviation in the above mentioned range?Does it play a role for the absolute temperature deviation if a 1N823 or a1N829 is used? Or is the behaviour equally when the individual zero TC current is used? Is the only difference between the selections that the zero TC current is more near the 7.5mA value on the 1N829? So is it more likely to get a low zero TC current of 4 mA on a 1N823 device than on the 1N829? Or should I go for the 1N829A for the lowest absolute TC? How large is the hysteresis on the zeners in a temperature range of 10-40 degrees celsius (50-104?F). On monolithic unheated reference voltages with hermetic case I have up to around 2 ppm hysteresis difference on temperature cycling. (see attached picture with 10-45 degrees celsius on X-Axis for an ADC with a 5V reference measuring a LM399 heated reference over a 2:1 precision voltage divider. The ADC with the 5V reference is temperature cycled). I blame the temperature hysteresis on the die attach to the lead frame which seems to be usually a silver filled epoxy compound. I hope that the hysteresis on a discrete zener is much lower. With best regards Andreas--------------------------------------------------Name: AD586_05_Hyst_20130120.PNG URL: <http://www.febo.com/pipermail/volt-nuts/attachments/20130126/4a3abca5/attachment.png> ------------------------------
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