Low loss 12v regulated output for 12v battery?

[e100]

I'm making a battery backup system to keep a modem and WiFi access point alive for as long as possible during power outages.
The network gear requires 12v although there's no spec given for the voltage tolerance. The combined current draw is about 1 amp.
I have a 12v car battery and a float charger so the battery voltage can go as high as 14.4v.

What's the simplest way of keeping the output voltage under control without unnecessarily wasting power?
I realise there are car 12v voltage stabilizers on ebay, but from the specs these appear to be a combined boost and buck converter. so I'm guessing that the efficiency isn't going to be that good.

I just need to constrain the output voltage to say less than 12.5v, but once the battery voltage voltage drops below that just bypass the regulator completely and run everything directly from the battery.

[mariush]

Power directly from battery.

Your networking gear may be powered using 12v adapters but internally, switching regulators are used to produce 5v, 3.6v , 2.5v etc
These will work with 11..13v a lead acid batterry can offer.

[Psi]

Also, any unregulated 12V adapter is going to put out like 16V peak anyway.
So most of the time they work fine running from a SLA being float charged at 13.8V.
(If it were me i would take the back of the gear and check the voltage of the input capacitors)


You do have to keep in mind that it's not 100% safe, you do see devices that really don't like more than 12V  +/- 5% from time to time.
A SEPIC regulator can be used if you want regulated DC output from the same voltage DC input.

[AE7OO]

You may want to take a look at this article at EDN.
https://www.edn.com/design/power-management/4442151/LM317-smooths-but-doesn-t-regulate

Not so much for using that 317(there are better regulators, to say the least) directly but between the article AND the comments you might get some ideas.

[Bratster]

Also, any unregulated 12V adapter is going to put out like 16V peak anyway.

When did you last see 16V on a 12V adapter? Unless it's a shitty primary side sensing adapter, I don't even think that's possible.
So far I've read a lot about primary side sensing, but I've never seen them in the wild. PC817+TL431 is literally all what I've seen, rest of some really high end ones that use better solutions.

The keyword there is unregulated.

So most likely a linear supply like things used to be in the old days.



Sent from my Pixel 2 XL using Tapatalk

[magic]

Also, any unregulated 12V adapter is going to put out like 16V peak anyway.
So most of the time they work fine running from a SLA being float charged at 13.8V.
(If it were me i would take the back of the gear and check the voltage of the input capacitors)

Unregulated adapters don't matter because network gear is universally shipped with regulated switchers, it's cheaper that way.

Take it apart, see what capacitors and voltage converters are used, check their maximum input voltage rating, problem solved.

So far I've read a lot about primary side sensing, but I've never seen them in the wild. PC817+TL431 is literally all what I've seen, rest of some really high end ones that use better solutions.

It's common in those tiny USB chargers where there isn't even enough space for PC817.

[Zero999]

I've seen some unregulated switched mode regulators which were really cheap: just a blocking oscillator!

But this was in a late 90s phone charger, not a modern piece of network gear, which as far as I'm aware, all use nicely regulated power supplies.

I still think it should be able to cope with up to 15V, with no problems. A higher voltage might even increase the life of certain components, since it would mean a lower current.