Hi,

Does anybody know how reduce the current but keep the volts the same, I don't wanna use resistors because of it effecting the volts and the current the only other thing I can think of is a diode.

I want to keep a constant volt of about 5.0 volts but drop the current from 20 ma to 3ma

Take a look here it's a good start... http://users.telenet.be/davshomepage/current-source.htm

Hi,

Strange request because: V=I*R so to keep a constant voltage at a lower current, the R has to rise. A current source as such will not help as it keeps the current constant but then the voltage has to increase until the designted current is reached. What voltage is reached is yet again dependend on the value of R and the rest of the circuitry.

But what do you want to do with the voltage/current? And what voltage do you want to keep at 5V (Supply or output) and why lower the current?

Wim

Yep Wim is right - your tied by Ohm's Law

Yeah I know thanks but it is the resistor route, What I want to do is, drop the Ma later on in my project after the regulators.

I wanna keep the Supply at 5 volts but the volts is still not decided on how high it needs to be yet:) I have found the Constant Current Buck Regulator http://www.national.com/pf/LM/LM3404.html but it is the opposite of what I want. Nobody has invented anything like this then:(

It is really messes way to create things like this, voltage and current up and down all the time.

Well yes and no lol at the moment I think it might be a diode,zener diode I will end up using that does not follow ohm's law somewhat.

What is it you are trying to do? Can you give us more details?

Hi Philips

So you want a supply volatge of 5 volt and use it to generate a certain current. Then a current source like pointe out before is what you need.

The current source should (if correctly setup) output a voltage below 5 Volt for the given current and resitance (V=I*R).

What you initially suggested isn't invented because it violates Ohm's law and therefore just is not possible. The LM3404 you mentions generates the current by generating a voltage high (or low) enough for the current to flow. Even a diode has a resitance (altough it depends on the voltage applied and has a sharp bend arourd the 1.2V and is not linear). Basically what the LM3404 does is keep the voltage drop across the resistor constant and thus the output current is stable. That simple.

So if you use a current source of 20mA with a led you always get around 1.2V output voltage no matter what you use as supply voltage (as long as it's higher that 1.2V off-course).

A zener diode also follows Ohm's law just like a led and a resistor. It's just not a fixed resitance. The current going through times the zener voltage will be dissipated as heat (P=V*I)!

This btw is why switching power supplies where invented (to lower heat dissipation and therefor increase efficiency).

Wim

it was just a DAC and some other projects no point in discussing any further tho

I don't like Ohm's law or Georg Ohm, I know somewhere in some part of this earth there is a material that can do this:) maybe on another planet then lol