24vdc to 12 vdc for remote deployment?

A 7812 is a linear voltage regulator, so it takes the 24V, and drops it to 12V. However, at 1A, that means the 7812 will need to dissipate 12W, which is far beyond it's capabilities.

A better solution would be a prebuilt dc-dc converter. You can get these all over the place. A quick search brought up this one:

However, there are lots to choose from. Size is an issue for you, so you'll have to be picky.

Richard, I found this page whilst doing some research but does it not go againnst what Robert write above? .i.e. the 7812 couldn't dssipate the power of the 9 to 12W that would occur?

Thanks

Stewart

My data sheet says the thermal resistance from junction to ambient, without a heatsink, is 65C/W, so 12W gives a junction temperature of

For a good TO220 heatsink, you get about 22C/W at 25C. We need to keep the junction temp < 125C. The resistance to case is 5C/W for the device itself. Thus, at 25C ambient, 25 + (5 + 22)*W < 125, so the power dissipation must be limited to 3.7W. This is assuming a perfect junction between the case and heatsink. That means that the maximum voltage input for 12V out at 1A is 15.7V.

Thus, unless I've added wrong, at 12W, a typical 7812 in this application, with or without a heat sink, will shut itself off in a few seconds.

You can get beefier linear regulators, of course, or use an external pass resistor to increase the maximum power dissipation, but then you need to deal with the heat.

A DC-DC converter is more efficient and thus cooler. It's more expensive, but for a single project, it is probably a better choice.

Have a look at