Take the 2-minute tour ×
Electrical Engineering Stack Exchange is a question and answer site for electronics and electrical engineering professionals, students, and enthusiasts. It's 100% free, no registration required.

There is a huge variety of Zeners that exist. They have varying breakdown pd among other things. Why then do we need voltage references that are more complex and made up of many components?

share|improve this question
    
This answer is useful: electronics.stackexchange.com/a/20737/30062 –  David Feb 18 at 13:03
    
Voltage reference ICs are usually more accurate, have a lower output impedance, and lower temperature drift than Zener diodes. –  Olin Lathrop Feb 18 at 14:43
add comment

3 Answers

All voltage references have a tolerance and a drift with aging and temperature. This list includes zener diodes, series voltage references (like voltage regulators) and shunt references (like the normal zener). Here's what a BZX84C zener looks like: -

enter image description here

Take the 5V1 device - its zener voltage range is somewhere between 4.8V and 5.4V for a zener current of 5mA - if you put more current through it some devices exceed the 5.4V limit - notice the column marked "dynamic resistance - this also indicates how this "perfect" voltage might vary with an increase in zener current. Devices like the 7.5v are much better at regulating but their potential drift is slightly higher (see temperature coefficient column). For this particular type of zener I would want, for a better quality of regulation to be choosing the 7.5V device. Notice also that at low zener values the leakage current and dynamic resistance and temperature coefficient are not very good.

The temperature coefficient column is not "parts per million" but hundreds of parts per million per ºC. Compare the lowly zener with (say) an ADR5041. It has an initial accuracy of 0.1% and a TC of 75ppm / ºC and there are better devices than this....

The LTC6655BHLS8-2.5 - it has a temperature drift of less than 2ppm / ºC. Hey, it costs a lot more but if you want a precise, reliable voltage reference for your 16 ADC then go for it. If you want accurate and reliable measurements you need a stable and precise reference. If you are just wanting to stop your MOSFETs gate being damaged by over-voltage then look no further than a zener diode.

share|improve this answer
add comment

Some of the best references available are actually "buried" zeners built into an ovenized arrangement (eg. LTZ1000).

Cheaper, noisier references are often made with band-gap references.

The parameters that vary between design choices include:

  1. Initial accuracy. Do you need +/-10% or +/- 0.01% accuracy?

  2. Drift with temperature or time. If it's a bias circuit you might be happy with a few percent drift with temperature. If it's a 6-1/2 digit multimeter reference you would want considerably better performance, down in the ppm/°C drift range.

  3. Power consumption. If you need a 1.25V reference to function with 50uA of current, a zener diode will not cut it.

  4. Noise. You may want a very quiet reference for a measuring circuit. Or you may want a noise source (zeners can be used for that).

  5. Compatibility. You may need a reference that can be incorporated into an IC, perhaps a CMOS IC.

  6. Price. You may have $100 to spend or 0.01 cent.

  7. Supply/Output voltage. Zeners are best around 6V. They're almost useless if you only have a 5V or 3.3V supply voltage.

  8. Load and line regulation.

Between all the above options, there are thousands of combinations, from the lowly 1N4742 and TL431, to the fancier precision references.

Beyond the monolithic world, there are even better references such as coulomb blockade and Josephson junction devices. At the lowest end, various diode junctions or \$V_{BE}\$ multipliers can be used.

share|improve this answer
add comment

Zeners have tolerances. They aren't commonly what you'd call "precision" devices. A 6.4 volt zener, for example, might be 6.4 +- 5%. They can also drift with temperature. If you need better tolerances than that, you either end up grading your zeners and throwing half of them out, or you get a more precise reference.

share|improve this answer
add comment

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.