30 volt, 15 milliamp max current power supply suggestions needed

Hello,

I need to build a power supply which has a 30 volt regulated (constant) voltage and also will be current limited to 15 mA max current.

I would like to use four 9 volt batteries hooked in series as the supply, and drop the voltage to 30v (regulated) somehow, as well as limit the current to a maximum of 15 milliamps ..

Thanks in advance for the help with this.

I was thinking of using an LM338 in constant current configuration:

**broken link removed**

As I understand this, Vref/R1 means Input voltage divided by the value of R1 so I would need to make R1 value of 2000 ohms, right? (30/2000=.015 amps).

If the above is correct, I just need to figure out how to regulate the input voltage from 36v down to a steady 30vdc. .

Here is the datasheet of the LM338 I would be using: https://www.electro-tech-online.com/custompdfs/2008/08/838621.pdf

I THINK I can use this same regulator somehow to do the voltage regulation I require. Suggetions, better ideas, all welcome..

I'd suggest the, L200CV. The circuit is on the datasheet which can be found using Google.

Why do you want such an unusual power supply for?

Another option would be to use a SEPIC converter and a single 9V battery but expect the input current to be around 56mA.

Are you wanting to build this because of it's simplicity? It is quite unusual. I suggest maybe building a traditional power supply using those old chestnuts...you know, bridge rectifier, Vreg, OVC and all that.

If I had a schematic for one that would give me the output I need, which would accept the input of my four 9 volt batteries, I would. .

I am exploring all my options at his point. My only requirements are that I need to power it with 36 volts dc input ( i COULD even go as high as 4 batteries, giving me input voltage of 45vdc), and need an output of exactly 30vdc and current limited to an absolute maximum value of 20mA.

I am even mulling over a scenario where i simply use a resistor to drop the voltage and a current regulating diode to limit the current. The only obstacle I have run into so far is that the only CRD's I can find regulate current to 22mA instead of 20mA.. (15mA is my ideal current target) That and I am not sure it will work..

The circuit will have very high resistance at first, but will eventually have lower and lower resistance, even to close to 0 ohms, thus i need the current regulation..


..

What kind of load will there be?

You still haven't said why you want to do this, it's possible you're trying to do something the wrong way.

Hi,

I am running current through water through submersed electrodes in order to create a colloidal solution of the metal.

The voltage and current need to be exact since I need all particles to be within a certain range of size, the more current used the bigger the particle size. I am shooting for very tiny particle size, thus the need for current regulation.

The solution at 1st has high resistance, then as more and more particles are deposited into the solution the resistance is lowered..

Do you really need to use batteries?

Two laptop power supplies in series could easilly provide 36V.

You are aware that you can't regulate the current and voltage simultaniously.

0x00x0 said:

a 30 volt regulated (constant) voltage and also will be current limited to 15 mA max current.

Click to expand...

So the V-I curve looks like a square; a flat horizontal line at 30 vdc, up until 15 mA is drawn, and then the curve goes vertically downward?