12V to 5V step down regulator VS. Switching regulator.

**HiJackZX1** · 11-06-2010, 06:57 PM

Originally Posted by OldSpark

A linear is at least 60% inefficient - ie, 7/12 (7volt drop from 12V).
If running at 14.5V, its (14.5-5)/14.5 = 65% inefficient.

If it drops 7V@16A, that's 7x16 = 112W in heat.
If it's 14.5V hence dropping 9.5V to 5V is 9.5V x 16A = 152W of heat.
And the input current will be 16A to provide 5V @ 16A = 80W output.

Switching regulators can be 90% efficient - eg; if 6A@14.5V = 87W input for 5A@16A = 80W output => 80/87 = 92% efficiency.

PS - that linear converter is a "12V/24V to 5V, Step-down, 20A, 100W". I hope the 100W simply means its output, not its thermal rating. IE; 5V@20A = 100W.
But max V-input if thermally limited to 100W is 10V for 20A, or (5 + 100W/16A) = (5+6.25) => 11.25V maximum for 5V@16A output (as opposed to dropping 112W & 152W at 12V & 14.5V as above).

So if it was your install, which would you get? The Linear or the Switching Regulator? The heat is concerning me on the Linear. I am starting to lean more towards the Switching now because PaulF uses one and swears by it. I havent seen anyone use the Linear and maybe the heat issue is why. Ive already spent so much money on my install, no reason to be cheap now, I'll just spend the extra money!

**OldSpark** · 11-07-2010, 01:19 AM

I'd get the Switching.
Else the switching.
Or at a pinch, the switching....

For small loads, linear is ok.
For big or otherwise, switching is preferred for efficiency, and often size.
Problem with switching is expense.
But those Mean Well switchers seem to be a very good price, and from what I hear, they are good & reliable.

Since the prices are so close in this case, switcher definitely.
Even at greater price differential, 100W of more of heat is a lot of heat; and wasted load (ie, equivalent to a pair of headlights...).

Just one thing - do NOT parallel PSUs - ie, don't connect two 10A linear OR switchers together to get 20A; keep them separate else buy the right size....

**HiJackZX1** · 11-07-2010, 06:10 PM

HEHE, noooooooo, I wasnt going to do that. I was going to put three KVMPs and maybe the ethernet hub on one switch. Then three KVMPs and maybe the Access Point on the other. So one would be 9.8 amps in use, the other would be 9 amps. Thats going by the adapter brick numbers, it will most likely be less then that.

**HiJackZX1** · 11-07-2010, 07:32 PM

I have a question though. I also have one USB hub that is on the OPUS 320. In the past the OPUS 320 would act funny with a USB hub. I would have to unplug the hub for the PC to boot correctly. Do you think it will do harm if I put the USB hub on one of the switching regulators and max it out to 10A?

**Flood_of_SYNs** · 11-21-2010, 02:35 PM

I believe they are both switching power supplies.

Here is some math that applies to linear regulators.

(12V - 5V) x 20A = 140W wasted as heat
(14.4V - 5V) x 20A = 188W wasted as heat

The largest heatsink I could find on digikey is one that can dissipate roughly 50 watts of heat.

I was googling around for a +5V supply for my truck, and the best I could find was a BEC for RC radios and it had a rating of 10A for ~$38.

The one from Current-Logic can do 20A and is about $25 plus it is epoxy sealed and waterproof.

I plan to buy this and mount it in my dash and use it for projects (Arduino / AVR) and for charging my iPhone.