Hi everyone. I am thinking about trying a new project but I could use a little advice. Say I have an application which uses around 15 watts. I realize this whole 15 watts thing is vague but it's really more about the idea. I only want to run the project off of one power supply, meaning I want the arduino powered off of the 15 watt supply.
Basically I am trying to use the arduino to limit the voltage to another circuit via PID (DC-DC converter & PWM).
You do not put an Arduino in series with the current. You use another device to carry the current and control it with the Arduino. They can run off the same supply.
If you are using a switchmode power supply, the voltage should be close to 12v, however if it is a transformer type, the voltage may be much higher.
If the Arduino is not being used to power any other outputs, 12v should be ok. If you plan to use the 5v out to run other things, the regulator may over heat.
The arduino may power one other small low current thing (20-60ma max). I guess my question is how do I divide the load between the arduino and the PWM IC or DC-DC converter but still power them off the same supply? Is there a way to have a powersupply give say 500mA to the arduino and 750mA to the DC-DC converter? I've done voltage divider circuits and stuff with op-amps, but I've never seen anything specific to current and can't think of anything.
I'm not seasoned with electronics which is probably pretty obvious.
As CR said, each load will use whatever current it needs. A power supply regulates the voltage but the current draw depends on the load.
In your case the Arduino will draw the small current it requires as will the load draw what it needs.
I query the need to use an Arduino for voltage regulation. Why not simply use a voltage regulator? There are many available for whatever voltage and current you may require.
I'm planning out an idea for an electronic cigarette with temperature control. I'm really happy you all were able to answer this for me, because I have been working on multiple projects but had so many issues with grounding that I almost always end up using 2-3 wall-warts per project. It's kind of funny when you teach yourself something, like I've done dual stage amplification circuits (TIA -> noninverting) and never learned how to handle power supplies. So I am going to go back and update some of these projects...
Thanks everyone for the help!
The idea is this, I will be sensing the voltage drop (probably across a resistor) in series with a resistive heating element. The heating element will be regulated by a DC-DC regulator. The change in resistance of the heating element/voltage divider will be proportional to the temperature of the heating element so I can PID (arduino) the voltage to lower or raise via an electronic potentiometer (DC-DC regulator). In this case only step down will really be needed.
The real short and skinny:
So the Arduino handle's the PID and sensing. Which controls the voltage regulator and thus the temperature of the heating element.
I probably won't even need PID, probably only PD but still.