How to generate DC 3V and 3mA current from 230V AC supply?

MaxHeadRoom

Joined Jul 18, 2013
20,927
The one thing with the supply in the link is it is a linear supply and generally are unregulated, the switching types are usually well regulated if you can get one in 3vdc.
Max.
 

KMoffett

Joined Dec 19, 2007
2,884
We don't know where you are. In the U.S. you can find regulated (SMPS) 3VDC wall warts at thrift/second-hand stores...or in you friends' or neighbors' junk drawers.
Ken
 

spinnaker

Joined Oct 29, 2009
7,835
The one thing with the supply in the link is it is a linear supply and generally are unregulated, the switching types are usually well regulated if you can get one in 3vdc.
Max.
But once you have the walwart, you can easily add your own regulation. Either with a linear regulator (a little easier) or a switching regulator (just slightly harder to do. In fact one of my very first "large" projects. I used a linear regulator. But with some of the new chips, it is actually pretty easy to design a switching regulator. TI really makes it easy for the design challenged with their online calculators.
 
The current will be decided by the load, you don't need a resistor, if 3v output?
Max.
Yes sorry I wasnt clear, I didnt understand what exactly he meant by 3mA, for example does he want to say run a led at 3mA, the phone charger will handle upto about 150mA (could be alot more I just dont remember), so maybe he needs a limit, I was going to say do a constant current driver, but he probably dosnt need that. I made assumptions and guess's, hence the resistor.
Sorry LED is bad example but you get what I mean
 

Thread Starter

mayurdehedkar

Joined Jan 12, 2014
10
I really thank you all for replying. I am from India. I want to generate a 3 miliampere current with 3 volt DC supply. I have 230V AC supply. I don't know how to convert this 230V AC input supply to 3 volt DC (with 3 miliampere(mA) current) supply. I have a Philips charger gives 4.7V and 70mA DC supply. But that doesn't work for the experiment. I have two choices, 1. to generate required current from 230V AC supply or 2. to reduce current from 70mA to 3mA. I don't have knowledge in electronics. I need circuit diagram or details to forward to a friend so that he can prepare it for me.

Mayur
 

THE_RB

Joined Feb 11, 2008
5,438
Since you already have a Philips 4.7v 70mA supply, you only need a 3.0v regulator IC.

These are very simple, one pin is GND, one pin is 4.7v in, the last pin is 3.0v out.

Please google for "3.0v 3-pin regulator" and you will find lots of cheap parts that will do what you need.
 

MrChips

Joined Oct 2, 2009
21,377
You could be confused about the 3V @ 3mA power supply.
In a power supply you control either the voltage or the current, not both at the same time.
Which do you want, 3V or 3mA?
 

ian field

Joined Oct 27, 2012
6,539
an old Nokia phone charger, I have one that is around 3V (3 or 3.3V I cant remember) use resistor to drop to 3mA
If you've got 3.3V and want 3.0V, the forward volt drop of a Shottky barrier diode will take care of somewhere close to the unwanted 0.3V.

The voltage dropped by a resistor will vary according to the current draw - so voltage regulation will not be good.
 

Thread Starter

mayurdehedkar

Joined Jan 12, 2014
10
There is an experiment in which cancer cells (in vitro)were treated with 1.5V to 3 V DC power supply with 3mA current. at higher current more than 20mA electrolysis takes place but at low current only enzyme -ribonucleotide reductase is inhibited and cell dies without producing toxicity. Hence 1.5V to 3 V DC power supply with 3mA current is required.
 

wayneh

Joined Sep 9, 2010
16,398
You cannot generally specify both voltage AND current, as this leave no degrees of freedom. In response to an applied voltage, a load will draw the current it does, as dictated by a number of internal factors; conductivity, cross sectional area and so on. You can instead control the current by varying the voltage, raising or lowering the voltage to get the required current. Only in a very narrow set of conditions will you have your 3mA driven into the load within the voltage range you cite. You would need to reproduce the cited conditions, and this means you'll need similar electrodes, distance between electrodes, and so on.
 

#12

Joined Nov 30, 2010
18,210
I'll try to say that simpler. If you give it a controlled voltage, the current will become what is dictated by the resistance of the sample. If you give it a controlled current, the voltage will become what is dictated by the resistance of the sample. Ohm's Law. V = IR You can't force both at the same time for an unknown and variable range of samples. Pick one.
 
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