I have the 0-5V output of the Arduino but it does not produce enough current. i would like to convert this to 0-5V with higher current.
i tried using a 2N4401 transistor but the voltage of the output was about 1/10th of what i need. Any suggestions?
What is "enough current"?
Use an external power supply to provide the 5V. An Arduino board is emphatically NOT a power supply
Please post the circuit that you tried when using the transistor
Which one?
...to power what kind of external device?
How? Schematic?
So 0.5V?
The load is a voltage controlled valve. Seems to draw too much power than the arduino can provide. i believe it is less than 100 mA.
Right now the 0-5V is a power supply. in the final product it would be an analog out from the arduino.
You do know that that will be a PWM signal (not really an analog voltage, as you would get from a variable power supply), yes?
Directly into a transistor base? BJT's are current amplifiers, you need a base resistor unless you use a MOSFET.
Definitely an "XY Problem" here. 
Perhaps read the instructions for posting at the start of each forum listing.
Then provide a detailed explanation of each part of your project, with full specifications (Web links) for the parts. Explaining which Arduino will suffice for that part.
This is..what? A smoke machine? Nothing limits the current through the base of the npn.
??? Why?
Btw, which Arduino board?
Hi,
No it won't.
The Arduino will switch the BJT/MOSFET ON and OFF with a small current, the BJT/MOSFET will then switch a larger SEPARATE EXTERNAL 5V supply to the load.
Tom... 
Ok. First I now realize that the arduino output is PWM and is therefore not suited for what I am looking for. That is fine ... I have a true analog out that I can use (and I will put a resistor in the base line).
This was just an idea that I tried. I am completely open to ideas on how to make this work. I've considered digital potentiometers and other items like that. This is a project for work so cost (within reason) is not an issue. What would people use?
How do you expect anyone to give sensible input if you don't specify what the mystery load is? So let's start there - what load are you powering exactly?
Something like this:
https://www.keysight.com/ca/en/products/dc-power-supplies/bench-power-supplies/e3640-series-bench-power-supply-30-100w.html
Why would PWM not work for a valve? Also why current and not voltage?
It is a air valve, a Conner valve to be specific. It takes a 0-5V signal.
That is a little out of my price range ... I need to produce several of these and this would be overkill.
PWM is not idea because this is a control signal as opposed to actually the signal that opens the valve.
Product type & datasheet please? I'd like to have some more info on how it needs to be/can be driven.
Hmmm... not what you answered before... you said money wasn't much of a problem. Perhaps you should define "within reason" more accurately so we can offer practical suggestions. I don't enjoy "what number am I thinking of" games...
Oh? This should be interesting ... a device that needs high current for a control signal. Takes me back to the old days...
Which "Conner" valve?
PWM is used to control proportional valves.
Hi,
What is the application, what do you need a proportional valve for?
Can you please post link to spec/data of the vavle?
If the 0 t o5V is a control voltage, why do you need that sort of current?
Tom...