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I am looking to use a 12V, 5 ampere car battery on a small 5V, 2A LED. Typical applications online use a resistor or voltage regulator, but since I am using a battery I would like to conserve power, if possible.

Is there a way to limit the current to this LED, ehile not draining excess power from the battery?

I'm ooking for a small/cheap solution, such as a BJT or MOSFET, but I am unsure of the most efficient way of doing so.

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    \$\begingroup\$ Does this answer your question? Efficiently limit current to led without power loss \$\endgroup\$
    – JYelton
    Commented Apr 4, 2022 at 16:51
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    \$\begingroup\$ Are you sure your LED is rated at 2A? If so, I wouldn't consider it "small." \$\endgroup\$
    – JYelton
    Commented Apr 4, 2022 at 16:55
  • \$\begingroup\$ "Does this answer your question?" No. A linear current regulator, linear voltage regulator, and single resistor all dissipate the same amount of power for the same operating conditions. \$\endgroup\$
    – AnalogKid
    Commented Apr 4, 2022 at 17:11
  • \$\begingroup\$ Welcome! ”12V, 5 ampere car battery” Stange. Do you mean 5 Ah? Even if so, that’s the smallest car battery I have ever seen by an order of magnitude. \$\endgroup\$
    – winny
    Commented Apr 4, 2022 at 17:14
  • \$\begingroup\$ LED are 3.5V max typically not 5V unless regulated with losses. The ideal solution is to match the load to the supply range or visa versa, like 11.5 to 12.5V to ?? So pls show link to LED or datasheet. Then if your priority is power efficiency , this is a must \$\endgroup\$
    – Tony Stewart EE75
    Commented Apr 4, 2022 at 17:35

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You are looking for a switching regulator. You can buy pre-made off-the-shelf modules from various sources, so you only need to solder the input and output wires. They may be labeled as "voltage step-down regulators" or "buck converters" - other slightly more obscure types are also suitable, such as "buck-boost converters" and "inverting converters".

Make sure to check the input and output allowed voltage and current. That's the main thing you are looking for. Many of them have adjustable output voltages, in which case make sure to set the output before connecting the LED.

Make sure it's a switching regulator. If it has a coil on it, it's almost certainly a switching regulator, although on the other hand, you might not be able to see the coil. You do not want a linear regulator as that's the inefficient type.

There are also ones designed to output a constant current, instead of the usual constant voltage, which can be useful for powering an LED, but those are a bit harder to find and aren't very useful for loads other than LEDs. If your LED is designed to be used with a resistor in series, then you will want to use a constant-current regulator instead of a constant-voltage regulator. If your LED is designed to be connected directly to a voltage source, use a constant-voltage regulator (the usual type).

You can also build your own switching regulator instead of buying one, but it's a bit more advanced.

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  • \$\begingroup\$ Thankyou! Exactly what i needed. Side Note/Question: As far as these buck-converters go, let say one is rated at 2amps. If i were to put a 3amp led on this, would the LED draw too much current, destroying the buck converter, or will this limit the current output, so the max current flow could be 2 amps, resulting in a dimmed LED. \$\endgroup\$
    – drew wood
    Commented Apr 4, 2022 at 17:50
  • \$\begingroup\$ @drewwood Depends on the converter. They can be designed to limit the current - they can be designed to switch to constant current instead of constant voltage, just like a lab power supply - but unless it actually says it will do that, you should assume there's a risk of damage. \$\endgroup\$
    – Stack Exchange Supports Israel
    Commented Apr 4, 2022 at 19:17

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