# Lowest deltaV buck regulator

#### BlightSpark

Oct 20, 2014
2
Greetings, leccytechies.
I've been asked how to run a 12V wifi router off a 12V car battery. I suggested a step down regulator but the ones I see need a minimum 1.5V difference (which would require 13.5V in battery).
Are there any buck regulators that can work from, say, 12.2V (200mV delta)?
Current draw is 0.5A max

Or do your great and powerful minds possess a more appropriate solution?

Many thanks

#### (*steve*)

##### ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
Moderator
Jan 21, 2010
25,510
One option is to use a boost regulator to step the voltage up to (say) 15V, and then a buck regulator to step it down to 12V.

That would give you 12V output even if the input voltage varies from several volts above 12V to several volts below. (the input voltage an even exceed 15V, the boost regulator wig generally just pass it through)

#### BlightSpark

Oct 20, 2014
2
It seems so obvious when someone else suggests it. Haha
Cheers *steve*

#### Harald Kapp

##### Moderator
Moderator
Nov 17, 2011
13,636
A SEPIC regulator is the circuit best suited for your application, as it will work when the battery voltage is below or above 12V.

Have a look at the 12V input specs of the route. Chances are that it will tolerate 10V...14V from the battery directly without any regulator as the internal electronics will not operate from 12V but a much lower voltage and therefore will have one or more internal regulators anyway.

#### (*steve*)

##### ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
Moderator
Jan 21, 2010
25,510
My experience is that SEPIC regulators tend to be quite inefficient, but a boost followed by a buck regulator will also suffer from this.

#### BobK

Jan 5, 2010
7,682
Theoretically, a buck regulator should work all the way down to the desired output voltage. In that case the PWM duty cycle becomes 100%. The only loss is the resistance across the switch element, which, with MOSFETs can be very low. I believe I have seen buck regulator chips that claim to work with near 0 delta V, but I don't feel like doing the search right now.

Edit: Go to ti.com, and use their wbench design tool. They will give you buck regulator designs that can output 12.0V from a 12.1V input.

Bob

Last edited:

#### (*steve*)

##### ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
Moderator
Jan 21, 2010
25,510
True, but you also have to recognize that a car battery can have the voltage fall below 12V.

However, this is a router. It has no business requiring 12V for anything. Internally it will be 5V or possibly 3.3V. There is a chance (approaching 100%) that there is a switch mode regulator inside and that the device will run from a wide range of input voltages,

I know of one device that could theoretically run from about 5V to 40V, but where the input capacitors limited that to 25V at the upper end. It too had a nominal 12V power supply as standard. Harald's suggestion in post 4 is on point. A regulator may not be required, but I would want to protect the device from voltage spikes!

Replies
3
Views
493
Replies
10
Views
2K
Replies
5
Views
1K
Replies
3
Views
2K
D
Replies
0
Views
1K
D