best way to drop from 12v to 5v dc? - better than a standard reg

[davecla]

I wanted to add a USB charging port to my car. I wanted about 1.5A max

I used a standard 7805 with a heat sink and that did the job - but got really hot under load!!!

Is there a more efficient way to do this that isn't too complicated? Dropping the power as heat must be very inefficient .

thanks
dave

 

[Pommie]

How about the **broken link removed**.

Mike.

 

[MikeMl]

Is there a more efficient way to do this that isn't too complicated? Dropping the power as heat must be very inefficient .

You have a 700W alternator under the hood. Who cares if you waste 10W? (especially in winter )

 

[crutschow]

You could also build a Black Regulator.

 

[OldTechie]

Yes, the linear regulators do waste a lot of power in the form of heat when there is a large difference between input and output voltages. The most efficient way to get what you want is with a DC-DC converter. Unless you have a specific need for the high current (1.5A) you asked for, it's really unnecessary if you only want to make a USB charger. If memory serves correctly, the USB spec limits available current to 0.5A, so any device you plug into it won't need more than that.
There are USB car chargers available (**broken link removed**) or (**broken link removed**). There are others of course, but these are examples.
If you want to build a DC-DC converter that will supply the 1.5A, check out National Semiconductor's Simple Switcher line (http://www.national.com/analog/power/simple_switcher) of SMPS chips. A caveat here... DC-DC converters can be a bit tricky to get working. Some are very sensitive to circuit layout, and are hard to troubleshoot (unless you have proper test equipment) when they don't work.

Cheers,
Dave M