Best Way to Achieve Stable 9V DC Output: 9V Battery vs Regulated DC Power Supply

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#1 21675782 23 Apr 2016 09:05

jr don jr don

Anonymous

Post #1
21675782 23 Apr 2016 09:05

I have an electronics project in which I have to maintain as stable a DC voltage as possible. The voltage has to be kept constant, with little to no ripple, at 9 volts. What is the best way of achieving this? How would using a 9 volt battery compare with using a DC power supply in how stable the voltage would be. Which would give better results?
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#2 21675783 23 Apr 2016 10:47

Dean Franks Dean Franks

Anonymous

Post #2
21675783 23 Apr 2016 10:47

It depends on whether you need a highly regulated voltage (exactly 9.000 volts) or low noise (9.0 volts with 0.00001 volt of noise).

Low resistance batteries (like NiMH or LiPoly) produce very low noise outputs if you don't need exactly 9 volts but you need low noise. If you need an exact output, you can use a low dropout regulator on one of these batteries to get a good compromise of both.

Typically, the voltage output will vary slightly by temperature and load current. Output noise from a low ESR battery is pretty low, but once you add a regulator you will get a more constant output voltage (across different loads and battery discharge states) but the LDO will also add noise.

A DC power supply can be designed to effectively eliminate ripple, but designing for very low output noise (
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#3 21675784 23 Apr 2016 19:28

richard gabric richard gabric

Anonymous

Post #3
21675784 23 Apr 2016 19:28

It would help if you specified more precisely what you want, how constant, what sort of stability, how much noise and ripple, over what sort of environmental conditions, what load current variation. Some idea of the application would help, since it could well define more precisely some of the values you need, and how much tolerance that there may be on then (maybe more than you believe), otherwise people like Dean cannot give you a better answer,
cheers,
Richard
#4 21675785 23 Apr 2016 20:51

jr don jr don

Anonymous

Post #4
21675785 23 Apr 2016 20:51

"It depends on whether you need a highly regulated voltage (exactly 9.000 volts) or low noise (9.0 volts with 0.00001 volt of noise)."

The answer is that it doesn't have to be highly regulated, but it does have to be low noise. So for example, if I were to set the voltage to 9 V, but it actually was 8.932 V that would be fine, but I would want it to remain steady at 8.932 V despite varying the resistance of the load by a few kOhms or the temperature of the environment by ~10 degrees C. I would want the noise to be as small as possible, and most important of all, I wouldn't want the voltage to drift over time.

With regards to the load, its total resistance wouldn't always be the same, but would be somewhere around 100-400 kOhms and may increase by about 10 kOhms every day or so ( I would want the voltage across this load to remain the same after this resistance increase takes place). With regards to much of the other questions, I don't yet know the answer to them. All I know is that I will need the voltage to be very constant, but I don't yet know to what tolerance I'll need. Its good to here that batteries work for this since this is a cheap option that I can just go an try out.
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#5 21675786 23 Apr 2016 22:10

Justin Spencer Mamaradlo Justin Spencer Mama...

Anonymous

Post #5
21675786 23 Apr 2016 22:10

Hi there,

Then what you need is an LDO. [Low-dropout linear regulator].

-Very low noise, can be as low as 60 uVrms.
-Regulates well too.

-the drawback: low efficiency

I'm not sure of charge pumps and buck converters because they're noisier.

Regards,
Justin
#6 21675787 23 Apr 2016 23:04

richard gabric richard gabric

Anonymous

Post #6
21675787 23 Apr 2016 23:04

From what you say, it does have to be highly regulated, but the absolute value is not as important. From your figures, you imply a stability of better than 1 part in 10,000, over 10 degrees C. Do you have a means of actually measuring this, what is the resolution, temperature coefficient and drift on the meter you have. Some battery types have significant temperature coefficients, so unless you can hold the temperature constant(or you can compensate for it), they will not meet your needs. You need to look up the curves of voltage versus temperature for the various battery types. Load is high, so self heating is not an issue. I think an Alkaline cell is around 1mV/4 degrees C, so you would get away with it if the temperature doesn't shift more than that temperature range, you need to check that out though.
There are regulators and references with noise down at the uV level, as Dean said, good references may have temp coefficients
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#7 21675788 24 Apr 2016 21:36

Justin Spencer Mamaradlo Justin Spencer Mama...

Anonymous

Post #7
21675788 24 Apr 2016 21:36

Hi there,

I was just wondering, are there references that regulate well
under a significant load?
If Mr. Don were to use a reference then it may not regulate well when
he loads the 100-400 kohms or so. Or maybe I'm not informed of
any well-regulating references (sorry, I'm still quite inexperienced).
I once tested the load regulation of a bandgap circuit and it didn't provide
a good curve (maybe because of the current limitation of the test pin/port).

It is really nice to learning a lot of things here in the forums, specially those
lessons that can only be learned through experience.

Regards,
Justin
#8 21675789 24 Apr 2016 22:51

richard gabric richard gabric

Anonymous

Post #8
21675789 24 Apr 2016 22:51

a Load of 100K to 400K was specified. The figure for deltaR was around 10K/day increasing.
A poor reference will have perhaps 50ppm/mA variation with load, a good quality one
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Topic summary

To achieve a stable 9V DC output with minimal noise and voltage drift, the choice between a 9V battery and a regulated DC power supply depends on the specific requirements for voltage accuracy, noise level, load variation, and environmental conditions. Low internal resistance batteries such as NiMH or LiPoly provide very low noise but their voltage varies with temperature and load, and they do not maintain a precise voltage level. Using a low-dropout (LDO) linear regulator with such batteries can improve voltage stability and regulation at the cost of some added noise and reduced efficiency. DC power supplies can be designed to minimize ripple and noise effectively, but achieving ultra-low noise requires careful design. For loads in the range of 100-400 kΩ with slow resistance changes, an LDO regulator is recommended for low noise (down to ~60 µVrms) and good load regulation. Battery voltage temperature coefficients (e.g., ~1 mV/4°C for alkaline) and measurement resolution should be considered to ensure stability over environmental changes. Bandgap voltage references may not regulate well under high load currents typical of the specified load range. Overall, an LDO regulator combined with a low ESR battery offers a good compromise for low noise and stable voltage in this application.
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Best Way to Achieve Stable 9V DC Output: 9V Battery vs Regulated DC Power Supply

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