Limit Current From 7805

Other Hardware General Electronics
1

I am working on a project where I will need to output 5v at around 500mA (or slightly less) from a ~12V source (motorcycle battery). I was thinking of using the 7805 regulator, but am not having second guesses. From what I have read it is more efficient to only supply about 3v higher than you need from the regulator. Anything more than that will be dissipated as heat. The other issue I have is the load (Android phone) is pulling well over 1.5A (which it doesn't need, but its taking what i can). I want to limit the output current at around 500mA. What is the best method of doing this using the 7805. Also would I be better off using a different regulator? Will I be putting out too much heat by supplying ~12V? Here is the circuit I am currently using for my regulator:

Thank you in advance.

2

I actually think I answered my own question. I apologize.

3

Some 7805 like : 78M05CT or L7805CT are the same in Voltage but not Current. Some are max 500 mA, some higher like 1 A or 1.5 A. Just do a search at http://www.datasheetcatalog.com/ and type the part number to download the datasheet. When a regulator goes behound the current rating, the regulator shut-down temporary, so make sure you know the total current being use and having a heatsink will help a lot, because when it is too hot, it will shut down.

Something to bear in mind about regulators.

4

Anything more than that will be dissipated as heat

No any excess above 5V is dissipated in heat.

The other issue I have is the load (Android phone) is pulling well over 1.5A (which it doesn't need, but its taking what i can).

Rubbish you do not understand basic electricity. If a device is pulling 1.5 A it needs the current, any attempt to limit the current will result in a lowering of the voltage and then the device will not work.

5

heats not really that big of a deal, just strap a hunk of metal on it and it will run happily with 500ma draw and 12 volts being applied to it ... the trick is to find a hunk of metal on a motorcycle :drooling_face: (just for clarity a hunk of metal that does not get hot, unlike the exhaust pipe)

celphones also often have a bit of work in the usb wall chargers, like a resistor pulling a data line one way or another ... so it will pull what it wants off of a charger, but I bet if you plugged it into a computer USB port it will draw less than 500ma, but charge slower.