# 12v regulator / voltage limiter

#### Slimat

Apr 8, 2024
5
Morning, I know there is a really simple solution to this and I am hoping someone can point me in the right direction.

I have a device which has a number of simultaneously lit LEDs and is being used in a car - the issue I have is that this is an old car and the battery voltage fluctuates between 12v (ish) and 14v when the car is running... this causes an issue where the LEDs pulse because of the fluctuating voltage. I did wonder whether something like an LM317 could be used?

I need a cheap solution which I can make to try and stabilize the voltage to be somewhere between 12v - 13.2v. Can anyone help?

Thanks

Last edited:

#### Harald Kapp

##### Moderator
Moderator
Nov 17, 2011
13,769
Look up 12 V buck-boost module. Here's an example for up to 36 W and a seemingly rugged construction for use in automotive applications.

#### Slimat

Apr 8, 2024
5
Thanks Harald I will take a look. The current drawn is about 1A, so 36W is more than enough.

#### Slimat

Apr 8, 2024
5
Just in case anyone else is looking for something similar this is what I have found...

Buck Converter

Do you think that would do the job?

#### Harald Kapp

##### Moderator
Moderator
Nov 17, 2011
13,769
Do you think that would do the job?
This is aq buck converter only (no boost function). The output voltage always needs to be less than the input voltage.
In your case this means that the LEDs will still flicker when the input voltage (from the battery) drops below 12 V. Unless you set the regulator to much less than 12 V, e.g. 10 V. The LEDs are possibly a bitt dimmer but constant so.

The regulator I linked to is a buck-boost type which measn the output voltage can be higher or lower than the input voltage. When you set it to 12 V, it will present 12 V at the output with input voltages between 8 V and 40 V. A short dip in th ebattery voltage should not be noticeable at the output.
You can find such a converter also in the form of bare modules as the ones you linked to.. But for use in a car you will need to add a case to prptect the circuit from environmental effects, mainly humidity and to prevent a short circuit between the module and the car's chassis.

#### ivak245

Jun 11, 2021
111
You could still use a LM317 and just set it at 12v, or a 3 terminal fixed 12V regulator (7812 etc) is cheap, and only needs a couple more parts to give you 12V out all the time. If the input goes below 12v, you will only get that at the output.

#### Slimat

Apr 8, 2024
5
Thanks @ivak245 I have ordered some of the buck-boost modules, as by my calculations I can get away with 10.8v - 13.2v as long as it is pretty stable, so hopefully these will land somewhere in that range. If not, then I will try to work out a suitable circuit with an LM3817 or 7812

Feb 19, 2021
787
This is a simple approach, not as efficient, as using buck / boost. For future reference,
driving constant current, so T and V effects always yield the same current thru LEDs.
Needless to say LM317 has to be heatsunk.

Note the series V of the 3 LEDs, each 2V in this sim, limit low voltage part of range.
So this works down to ~ 10V. If you series only 2 LEDs then down to 8V would be result.

Dont forget to mange load dump in a vehicle :

Regards, Dana.

Last edited:

#### Slimat

Apr 8, 2024
5
This is aq buck converter only (no boost function). The output voltage always needs to be less than the input voltage.
In your case this means that the LEDs will still flicker when the input voltage (from the battery) drops below 12 V. Unless you set the regulator to much less than 12 V, e.g. 10 V. The LEDs are possibly a bitt dimmer but constant so.

The regulator I linked to is a buck-boost type which measn the output voltage can be higher or lower than the input voltage. When you set it to 12 V, it will present 12 V at the output with input voltages between 8 V and 40 V. A short dip in th ebattery voltage should not be noticeable at the output.
You can find such a converter also in the form of bare modules as the ones you linked to.. But for use in a car you will need to add a case to prptect the circuit from environmental effects, mainly humidity and to prevent a short circuit between the module and the car's chassis.
Ah, thanks Harald... I missed that those weren't buck-boost models... so will take another look. The case is not too important to me as this is to be fitted inside a housing I have 3D printed as this is to go on my race car... size is more important as I really need this to fit into a 53mm diameter circular case... but what I may do is fit a buck-boost circuit to the source supply from the fuse which feeds this unit... that way I can use the bulkhead as a heatsink and when the supply gets to the unit it should be a steady 12v all the time...

Thanks everyone for some great advice

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