Any infos on µA circuits?

[Zen_]

Hi,


would button cells battery be the best choices for portable projects with circuits with these specs: 03 - 1.1v (max) 0.1 - 3µA (max)?

I do not find circuits as references or examples.

Any informations or suggestions would be appreciated!

 

[Harald Kapp]

Depends on how you define "best".

• size
• lifetime
• weight
• rechargeable yes/no?
• prize

 

[Zen_]

Thank you for your reply.

I need to generate DC with no deviations of voltage or current above max values (the load will be tissues samples, and dynamic resistance will be tested as it varies)

- it depends (can be adjusted) in regards to the circuit.

-At 3µA (max) for 3 to 7 days.

-2.5g max (with circuit 4.5g)

-no (will be replaced when needed)

 

[Harald Kapp]

3 µA -> 3 µA × 24 h = 72 µAh per day,
3 days -> 3 days × 72 µAh/day = 216 µAh capacity required.
Button cells come in many different sizes and capacities. Select one that fits your needs in terms of capacity (aka lifetime), size and weight. See here for a rough overview. Look up the datasheet of the cell of your choice for specifics.

 

[Zen_]

The only issue is that the entire circuit would need to be of similar size and i have no examples (3µA is max - 0.1 is the reference)

If you have any examples of such a circuit, i would really appreciate any infos.

I have looked at the data and the end point voltage is of concern, and i see no details on this.

 

[Harald Kapp]

If you have any examples of such a circuit

Which circuit? You asked about batteries.
It makes no sense to ask for just any circuit that draws 3 µA or less. You need to specify the function of the circuit.

I have looked at the data and the end point voltage is of concern, and i see no details on this.

Where have you looked? What have you looked at?
Please state clearly what the problem is. Of course any battery loses voltage over time. In your first post you state a voltage range from 0.3 ... 1.1 V, This is quite wide a range.

 

[Zen_]

I thought that indication on batteries would help me find more details or similar projects.


I have looked at various links on end point voltage on button cells (no particular references) they do mention "fast drop".

I'm trying to replicate a study who used a "galvanic current response" circuit (the terminology of the papers)

Electrodes connected to a circuit, to elicit direct response with controlled voltage and nA to µA current, to tissues samples.

There are mention of "button cells", as well as other DC supply who have been tested (but no details)

The max values indicate negative range (0.3 positive and 1 to 1.1v a limit and toward negative elicited effect) in regards to biological response in tissues.

Constant current is essential (no deviation during at least 72h of contact with tissues samples)

There are no schematics, only preliminary results (There a vastly more informations on temperatures, tissues samples, containment, etc...)

All informations present indicate an extremely simple circuit.

 

[Zen_]

The informations above is all the details contained in the study (on the device)

This type of research is discussed (µA DC) the values are different (and power supply).

How do I generate ~50 microamps of DC across dynamic resistance?

 

[Nanren888]

Consider a lab instrument? Somewhat different form factor, I understand.
There are instruments that are programmable power sources; you tell them the voltage or current and they set to it, accurately.
.
Possible to build yourself ones that are fixed, or even set variable, but as the accuracy required gets tighter, the intricacy of the circuit design also goes up.
Until we have an idea of the what you actually want, difficult to guess what sort of circuit you are talking about.
.
Is it a button cell in & a DC-DC converter to a variable, preset each use, current source output you need?

 

[Zen_]

Device is similar to EMS/TENS unit (with electrodes on tissues samples)

Button cell would be preferable (portability) output 0.5v - 0.5µA (constant current)

 

[Harald Kapp]

output 0.5v - 0.5µA (constant current)

You can't have both voltage and current fixed. Acc. to Ohm's law the voltage for a given resistance is V = R × I where
I = current (supposedly constant)
R = resistance (varying, depending on the tissue samples)
It seems what you are looking for is a constant current source with I = 0.5 µA. Loads of circuits can be found for a constant current source along with equations for calculating component values. The real challenges are:

• The very low current of 0.5 µA
• The requirement for operation from a single cell

The low current is in the range of the quiescent current of most of the integrated solutions I scanned quickly. I doubt you can build a solution based on your requirements for size and battery voltage at reasonable cost. The typical opamp or transistor based current source will draw a multiple of the 0.5 µA as quiescent current alone.

 

[Zen_]

The output of 0.5v (can be 0.4v to 0.6v) is mentioned as correct (anything above 1.1v regardless of current is "negative")

Current of 0.3 to 0.4µA is efficient (max 4µA is considered the limit)

What is required is few components, single button cell, and constant current.

 

[Alec_t]

constant current.

We know you want something in the 0.3μ to 4μ range, but how constant? ±10% tolerance?, ±1%?, ....?

 

[Zen_]

These are the informations contained in the study, there are no details.

Deviations (above correct margin) is described as "negative" response, everything within the margin of values mentioned is described to be correct.

Only increases are mentioned to be negative.

±1% tolerance (from informations present in the document)

The values of 0.3 to 4µA elicit similar response (example 0.9v - 4µA "correct", 1.3v - 0.1µA "negative")

 

[Harald Kapp]

These are the informations contained in the study, there are no details.

So the first task i for you to thoroughly read and understand the study. We'll be happy to help with details of implementation. You don't expect us to study the study, do you?

 

[Zen_]

The informations (voltage, current and negative - postive effect) is what is described in totality about the "circuit" in the study.

All the informations, details, analysis and hypothesis concern the tissues samples selections, reactions.

The difference of this study is the values which are not usually studied.

There are no technical references to similar circuits or devices (in patents or study) effective in those ranges (most are in mA)

There are no schematics (or picture of the circuit), the preliminary informations on the study do not consider that the circuit itself deserve elaborate explaination (as no details is present in the papers only the values who are discussed in details).

Based on the study, it seems a similar circuit is a simple project (the tissues samples analysis requiring the majority of the attention)

 

[Alec_t]

would button cells battery be the best choices for portable projects with circuits with these specs: 03 - 1.1v (max) 0.1 - 3µA (max)?

If all you have to power any proposed circuit is a button cell, I don't see any obvious way of creating a constant current source (albeit only a μA or so) able to maintain the current within a ±1% tolerance.

 

[Nanren888]

Based on the study, it seems a similar circuit is a simple project (the tissues samples analysis requiring the majority of the attention)

This is often the way for one of two reasons.
When I look at doing something, or how to do something, I automatically focus on the parts that I know about. Anything that I do not have to do, I do not need detailed knowldge of, so a passing understanding will do. So only my part seems complicated. Also, I have little idea how to even specify the important paramters of the parts I just want to use, without further involvement. Everything else is sort of described by, well that part should just do its job.
The other reason is that might be available. either because an instrument is available, or I don't really care about the parameters and I write up what I used, or had, as if that is the only option, or more importantly so someone else knows how to repicate.
.
Can you share the reference?
We might be able to sort out what's actually required.
.
Generally batteries offer a power source, voltage source. Many run at almost a constant voltage for some time, then as they drain, the voltage drops. Some battery technologies seem pretty flat, same voltage, then drop off to dead quickly. Others droop slowly, running at lower voltage for some time before dieing..
Many things we would like to power offer a sort of constant resistance, so the current is proportional to the voltage. Some other things like biological or chemical cells can have characterstics that change over time.
If we want the current fixed to some known value we generally have to put a circuit between the battery, or other power source and the load that will measure the current & keep adjusting it to keep it constant. It does this by keeping changing the voltage till the current is right. When things get too far out, like the battery if flattening, they fail to keep things constant.
.
So, a constant, even small, current into a biological specimen, with not much more than a button cell?, not really.
(1) If the cell always starts from new & does not have to last long AND the cell is always the same, then with some experimentation, you could choose the right resistor to put between the battery cell and the biological cell to make the current correct. This will be approximately right given battery tollerance, and cell tollerances, till the battery voltage droops. It won't regulate, so given those possible diffferences of battery & one cell to another , not likely within 1% too often or for too long.
(2) Make a constant current circuit that regulates. No problem there. That circuit will use power, probably more than the load current, so you'll need a bigger power source for it. It can run off a button celll if you must with appropriate converters & constant current source circuit, but ot will drain faster. Someone needs to design it. As mentioned above, there are many curcuits for constant current sources online. Some simple & some sophisticated. If you want good regulation, that is accurately controlled current, you're want more sophisiticated. As mentioned above, the currents many components are designed for can be as big or greater than the one you want in your load, so two things. (1) the control, constant current, circuit will consume more power than the load and (2) some carfeul design may be required so leakage current don't swamp your measurements that are the basis of the control.
.
Sorry, I didn't really get your setup. I couldn't imagine any meaningful thing that matched your explanation that would not be done in a lab. So using standard lab equipment is often the easiest way rather than reinventing the wheel. But constant current circuits are plentiful; Could be done.
.
Hope this helps. Hope I've been clear. Don't think I've included anything really new, just summarised those above.

LM134/LM234/LM334 3-Terminal Adjustable Current Sources
(Programmable From 1μA to 10mA)

https://www.analog.com/en/products/...omplete,by instrumentation and test equipment.

 

[Alec_t]

After doing a bit of googling I now think you could use a 3V lithium cell to power a constant-current source. There are micropower 1.25V voltage references available (e.g. LTC6656-1.25) and micropower op-amps (e.g. MAX40006). Something based on the attached circuit might meet your requirements, so far as I understand them. If this project is for in vivo use rather than in vitro you would have to adapt it if necessary so that it meets any legal requirements in your country.



The Sample current here is 2μA, set by resistor R1 (increase R1 to reduce the current, reduce R1 to increase the current). The LT6656 draws <1μA and the MAX40006 draws <5μA, so the lithium cell should run for a long time.
I'm attaching my simulation file.

 

[Zen_]

Hi,

the study is not peer reviewed and was not made public outside of the university (the access is part of preliminary work on a similar subject)

I can details part of the study (which are found above in the previous messages) but not actual applications nor the conclusions.

The study is in vitro.

Thank you for the excellent suggestion on the LTC6656-1.25 and the configuration presented.

Would there be a possibility to keep a similar number of components but with the output under 1v?

these devices while completely different in applications than the study discussed (In vivo applications, different specs, etc...) are portable, require button cells and relatively simple circuits.

http://www.nlvocables.com/blog/?p=609