loading

Reducing Current While Leaving Voltage the Same

Hey, I have a power source that puts out 5V at about 2A. I need to reduce the current to 1A while maintaining 5V. How would I go about doing this? I thought about a resistor, but since the voltage drop is 0, how would I calculate what value I would need?

EDIT: I was also looking at regulators, like this one. It says it limits current to 1A, but I'm not sure if it would be useful for what I need...

http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=MCP1826-5002E/AT-ND

sort by: active | newest | oldest
westfw8 years ago
If you're trying to connect a device that is supposed to use a 5V 1A power supply to a 5V 2A source, you can probably just go ahead and do it (as long as it's a REGULATED 5V 2A supply.) A regulated 5V 2A supply won't FORCE 1A though your device, and your device won't draw 2A just because it's connected to a source that could deliver it; for practical purposes, this is what "regulation" means.
msh21 (author)  westfw8 years ago
Thanks for the reply! I tried connecting my iPod to the power source and it shut off. Luckily, there is no permanent damage. My power source is 4 rechargeable AAA batteries in series, rated at 1.2V, 1000mAh each. Somehow I seem to be getting more voltage and current than is advertised. I don't know if this is considered a "regulated" supply. If its not, is there anything I can do to make this work?
lemonie8 years ago
Think about just limiting the current with a resistor (if you need to - westfw). What you get out of a power supply depends upon what you connect to it - what do you want to use?

L
msh21 (author)  lemonie8 years ago
Thanks for the reply! I'm trying to power an iPod. I'm actually surprised I am having this problem because the four rechargeable batteries I bought say 1.2V, 1000mAh each. I seem to be getting more voltage and current than they advertise.
lemonie msh218 years ago
iPod batteries are 3.7V so I'd expect you to be able to run the thing on 3 of your rechargeables. For charging it I should think the iPod will be fine on the 4 as they are. Voltages vary with load and charge, see what you get when they're actually powering the thing?
Is the iPod in or out of warranty?

L
msh21 (author)  lemonie8 years ago
The iPod I plan on charging is in warranty. I have another, older, iPod that is out of warranty. I tried using the batteries on the older one and it shut off immediately. Luckily, no harm done, but I know that something must be wrong. It has to be the amount of current.
PKM8 years ago
As the others have said, it depends what you want to power. Your power supply doesn't always put out exactly 2 amps, it puts out the amount that is drawn up to 2 amps (and could possibly put out more but might be at risk of voltage sag or overheating). If your device draws 1 amp it will draw 1 amp no matter what 5V power supply you connect to it.
kelseymh8 years ago
You can't. Unless your load is superconducting, it will always have some resistance. Given Ohm's law, V = IR, to keep the current I constant, V has to drop proportionately.

The HV power supplies used on my drift chamber are current-limiting supplies. If the current drawn by the load (a group of HV sense wires in the chamber) exceeds the set limit, the voltage is reduced so that the current stays at that limit.