Ok, for fun and enjoyment I have decided to build in chargers in a number of positions on the "Mom Van." But either I can't do math, or I am missing something. I want tablet style chargers capable of 2 amps, but when I do the math--basically I'm going to set the car on fire. I chose:

A to-220 5v rated to 2 amps https://www.mouser.com/datasheet/2/389/l78s-974158.pdf

And there will be heat sinks--currently thinking of these: https://www.mouser.com/datasheet/2/303/sink_csm-1265487.pdf

My problem is that with a voltage drop from 14.4 to 5 and at 2 amps I get (9.4v)(2A)=18.8Watts. Take the 50C/W rating from the data sheet and I get a temperature rise to air of: 50C(9.4)=940C.

I could buy these chargers for a couple bucks (but this is more fun, and I want them built in seamlessly)

I must be missing something? Any help would be appreciated!

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    \$\begingroup\$ And now you know why no one uses linear regulators for this. \$\endgroup\$ – Ignacio Vazquez-Abrams May 7 '18 at 6:19
  • \$\begingroup\$ See Figure 27 . \$\endgroup\$ – Ignacio Vazquez-Abrams May 7 '18 at 6:20

Your math is correct. Although 940 C is a bit high, they usually limit around 120 C. You will still create a nice heater using linear regulators. Which is why people don't use them for a big drop in voltage.

Today we use switching power supplies.

And there are little modules as easy as those linear regulators.

They are more expensive directly compared to a single linear regulator. But it will earn itself back if you look at the whole project, and wasted energy during usage.

  • \$\begingroup\$ Thanks! Totally willing to spend a few dollars to do it right, my ignorance was blocking me. I'll go find some switching power supplies. \$\endgroup\$ – Kyle Suzenski May 7 '18 at 17:41

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