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This is a theoretical question. I know two sources of power as of now: SMPS (Buck/Boost Convertor) and Linear Regulator. Of these two, a linear regulator is the one with the least noise.

I would like to know if there are options even better than linear regulators. I have heard batteries provide power with the least noise.

Any other option than batteries?

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    \$\begingroup\$ Not any of those devices except batteries are power sources. FYI \$\endgroup\$
    – MiNiMe
    Commented Sep 28, 2023 at 9:02
  • \$\begingroup\$ @MiNiMe Sorry, I meant the final link in the power supply, or maybe need better words, but you get my point. \$\endgroup\$
    – John Snow
    Commented Sep 28, 2023 at 11:10
  • \$\begingroup\$ Oh ok.@Saadat gave a good answer then :) \$\endgroup\$
    – MiNiMe
    Commented Sep 28, 2023 at 17:13

2 Answers 2

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Regulators

Generally speaking, it's not easy to answer this question. There are SMPS regulators that have lower noise than the normal Linear regulators. The downside is they are more expensive.

If you need a low noise linear regulator that is more stable than normal linear regulatros, there are linear regulators designed for such purpose. These are usually used for analogue referencing and are limited in sourcing current. For example, LT3045 is an ultralow noise regulator that can source up to 500mA.

LT3045
20V, 500mA, Ultralow Noise, Ultrahigh PSRR Linear Regulator

Notice that the feedback needs to be connected close to the output capacitor so the regulator can operate properly and reject the ripple and noise from the output.

Batteries

The batteries are very good, as we can assume they don't have internal noise. This means if you are not drawing current from the battery, it's completely noise-free. However, if you are supplying a load, and the load is noisy (there is a ripple on current), then the internal resistor of the battery becomes very important. That internal resistance will create ripples on the voltage of the battery terminals.

This means the lower the internal resistance of a battery, the more stable the output. For example, a Li-Pol battery has a very low internal resistance compared to a Ni-Cad battery. So, for a specific noisy load, if you use a Li-Pol battery, you will end up with lower noise on the battery terminal.

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  • \$\begingroup\$ See, this is why asking just broad theoretical questions is always good, you get broad answers which are so much more educating. Thanks. I didn't know this about batteries. I will tell you what, I realized long back that sensors should be powered via linear regulators for low noise power, but that was before I thought of batteries (I am an amateur, I learn new things every day). I "assumed" batteries would be quieter than say an AMS1117, and you are saying that is not necessarily the case? That a Li-Po might be low noise but not Ni-Cad? \$\endgroup\$
    – John Snow
    Commented Sep 29, 2023 at 9:08
  • \$\begingroup\$ Also, if its a rechargeable battery, and we are charging it while at the same time drawing power, would we not start drawing from the charging source? effectively eliminating any benefits of the nattery's low noise characteristics? \$\endgroup\$
    – John Snow
    Commented Sep 29, 2023 at 9:12
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    \$\begingroup\$ I'm glad it was helpful. For the first question, all I'm saying is that the better the battery (lower resistance), the lower the voltage ripple would be. It depends on the way that your load would use it. If it's a constant current load (like a resistor), both batteries would do the same after connection (just a small difference in voltage drop at the start). For the AMS1117, if you use a proper capacitor, for most of the applications the ripple on output is acceptable. For the same resistive load, the output ripple will depend on how good is your source power supply for input. \$\endgroup\$
    – Saadat
    Commented Sep 29, 2023 at 9:37
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    \$\begingroup\$ For the second question, generally speaking, yes. The chargers are usually the cheapest SMPS solutions and are very noisy. The battery absorbs most of the noise (again, the internal resistance plays a big role here). Still, there will be a ripple on the battery terminals. If you are powering a sensor that directly affects the reading (like a Wheatstone Bride or similar), then go with the ultra-low noise regulators. If it's for a sensor module, most of them have some filters on the module to reject this type of noise. \$\endgroup\$
    – Saadat
    Commented Sep 29, 2023 at 9:42
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If I read your question right, that is, comparing regulators / switching components, you want a source that delivers a clean voltage.

  • Batteries as you stated
  • Capacitors
  • Photo voltaic panels
  • Fuel cells
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