How to make a constant current DC power supply?

[ashayalmighty]

Hello!
I want to make a DC power supply that turns 230V-240V AC (236V to be exact according to my multi-meter) to DC with constant current of upto 15mA.

Is it possible to also have a regulator to gradually change the output DC current from 1mA to 15mA ?

What effect will having a constant DC output current have on the DC output voltage?

Thanks!

[eccerr0r]

Re: How to make a constant current DC power supply?

Well, a theoretical constant current power supply of 1µA connected to a theoretical open circuit will have a theoretical potential of infinite voltage, so you need to make some clarification on what exactly you want because of the constraints of "real" components available...

Most constant current PSUs are extremely voltage limited because of the problems of real components, so you have to put that as a constraint.

[PeteS in CA]

Re: How to make a constant current DC power supply?

Assuming you would use a transformer to step down the voltage and to provide isolation (safety) there's a circuit that might be useful in the application notes for the LM317 adjustable positive regulator.

[budm]

Re: How to make a constant current DC power supply?

Assuming you would use a transformer to step down the voltage and to provide isolation (safety) there's a circuit that might be useful in the application notes for the LM317 adjustable positive regulator.

+1
And also do you know what is the highest resistance your load will be for maintaining 15mA of constant current.
BTW, why 15mA?

[eccerr0r]

Re: How to make a constant current DC power supply?

My guess would be LEDs but no idea, hence wanting clarifications on constraints...

[ashayalmighty]

Re: How to make a constant current DC power supply?

Sorry for late reply.
I am trying to make an iontophoresis device for palmoplantar hyperhidrosis.
From what I've read, it requires a constant DC current.

[budm]

Re: How to make a constant current DC power supply?

Are you referring to something like this?
What research did you find that you need 15mA of constant current?
You can easily make CC source using LM317 as suggested.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4812886/
http://www.jcasonline.com/article.as...56;aulast=Jain
https://www.rafischer.com/direct-vs-...is-comparison/

[eccerr0r]

Re: How to make a constant current DC power supply?

Ooh medical devices... this goes into a lawsuit problem. We'll have to caveat that all of this advice is at your own risk.

That being said, the amount of current going through the body is going to be limited by the resistance of the body so you merely want current limiting to not electrocute the user. If you use a battery, all you need is a resistor for current limiting to a maximum of 15mA before you shock the person to death. I'd suggest not using mains power if you don't know how to make medical electronics (and I do not.)

Also the metal used for the probes, you'd better be using noble/inert metals else you may poison the user, but you'll see this as corrosion first....

[ashayalmighty]

Re: How to make a constant current DC power supply?

Are you referring to something like this?
What research did you find that you need 15mA of constant current?
You can easily make CC source using LM317 as suggested.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4812886/
http://www.jcasonline.com/article.as...56;aulast=Jain
https://www.rafischer.com/direct-vs-...is-comparison/

Yes, the articles you have linked are DIY iontophoresis devices with a battery, but the battery operated apparatus does not have the same efficacy as the plugged ones, even if the battery were to provide a constant voltage it won't provide a constant current.
The constant current is for the safety of the user and accuracy of the measurement.
Many articles I read suggested that using higher current gives better results, although the maximum current should be set according to the comfort of the user, if the user has higher pain threshold he/she can use higher current upto 25mA without causing any serious injury or discomfort so as to be able to perform the iontophoresis therapy.

https://www.iontodevice.com/hyperhid...rent-t139.html

https://allumiax.com/blog/ac-vs-dc-w...more-dangerous
This article states that the resistance when the palms are immersed is around 200-500 ohms

[budm]

Re: How to make a constant current DC power supply?

"This article states that the resistance when the palms are immersed is around 200-500 ohms" is that measured between two hands?
But your body resistance is not 200 ~ 500 Ohms (internal body having at least 300-500 ohms per article and also affected by fat content). You are forcing current through your body via your hands, look at how the connections are made..
BTW, to maintain constant current, the Voltage will have to vary to maintain constant current flow.

[ashayalmighty]

Re: How to make a constant current DC power supply?

Ooh medical devices... this goes into a lawsuit problem. We'll have to caveat that all of this advice is at your own risk.

That being said, the amount of current going through the body is going to be limited by the resistance of the body so you merely want current limiting to not electrocute the user. If you use a battery, all you need is a resistor for current limiting to a maximum of 15mA before you shock the person to death. I'd suggest not using mains power if you don't know how to make medical electronics (and I do not.)

Also the metal used for the probes, you'd better be using noble/inert metals else you may poison the user, but you'll see this as corrosion first....

I am not gonna use the apparatus for commercial purpose.
The probes will not be immersed in the water, they will be connected to the container filled with the water, may be the container need to be inert?
Will using fuse not be enough protection?

[ashayalmighty]

Re: How to make a constant current DC power supply?

"This article states that the resistance when the palms are immersed is around 200-500 ohms" is that measured between two hands?
But your body resistance is not 200 ~ 500 Ohms (internal body having at least 300-500 ohms per article and also affected by fat content). You are forcing current through your body via your hands, look at how the connections are made..
BTW, to maintain constant current, the Voltage will have to vary to maintain constant current flow.

I agree the voltage will have to vary.

[eccerr0r]

Re: How to make a constant current DC power supply?

Perhaps instead of 'probe' probably should use 'electrode' alas it's still the same problem - the person is going to be deliberately contacting some water and the electrode. Even if this is not "commercial" it's still medical use, especially if you're planning to use it on someone else.

A fuse will not help against electrocution, careful design is all you can do.