Source: https://mokxi.com/learn/arduino-lm2596-buck-converter Updated: 2026-11-02 Learn # LM2596 buck converter: power an Arduino from 12 V Beginner Written by the Mokxi team, updated November 2, 2026 Start building free Open the editor Or see every lesson. - 465 parts on the bench - 43 boards running now - 1.00x real time, on every board Click to open it in the editor A 12 V adapter into an LM2596 set to 5 V, its output on the Uno’s 5V pin, and A0 reading the adapter. Press Run, then set the adapter to 9 V. The LM2596 module is the small blue board with a brass trimmer that turns 12 V, 24 V or anything up to 40 V into a lower voltage you pick. It is a buck converter, a step-down switching regulator, and it is the usual way to run an Arduino, a servo or an LED strip from a 12 V wall adapter or a battery pack without a regulator that runs hot. The circuit above is an Arduino Uno on a 12 V adapter: the adapter into the module, the module set to 5 V into the Uno’s 5V pin, and A0 reading the adapter through a 10k and 4.7k divider. Press Run and the serial monitor prints "A0 785, adapter 12.0 V". Swap the adapter for 9 V and it prints "A0 589, adapter 9.0 V" while the 5V pin stays at 5.0 V. ## What you need - An Arduino Uno (or any 5 V board) - An LM2596 buck converter module - A 12 V wall adapter and a DC barrel jack - A 10k and a 4.7k resistor, for reading the adapter on A0 - A multimeter, to set the module before anything is on its output ## Wiring Part and pin | Goes to | Note Adapter + | LM2596 IN+ | 4.5 V to 40 V in Adapter - | LM2596 IN- | LM2596 OUT+ | Uno 5V | Only after the trimmer is set to 5 V LM2596 OUT- | Uno GND | IN- and OUT- are the same copper on the board Adapter + through 10k | A0 | 4.7k from A0 to GND ## Set the trimmer before anything is connected A module comes set to whatever the factory left it at, often well over 5 V. The Uno’s 5V pin goes straight to the chip with no regulator in front of it, so a module set to 12 V on that pin kills the board. Put the adapter on IN+ and IN-, a meter on OUT+ and OUT-, and turn the brass screw until the meter reads 5.0 V. The trimmer is multiturn, so expect a lot of turns before the reading moves much. In Mokxi the trimmer is the module’s volts property, from 1.23 V to 37 V. Before Run the module’s label shows the setting; while it runs, the volts on OUT+. ## Why a buck converter and not a 7805 A 7805 or the Uno’s own regulator gets to 5 V by burning the difference. At 200 mA from 12 V that is (12 - 5) x 0.2 = 1.4 W of heat, and the 200 mA all comes out of the adapter. The LM2596 switches its input on and off 150,000 times a second and an inductor smooths it, so it trades volts for amps instead: 5 V at 200 mA is 1 W, and at about 85 % that is under 100 mA from 12 V. On the engine, 12 V in and 5 V out into a 1 A load takes about half an amp from the adapter, about 86 % efficient. At 3 A it is about 82 %; TI’s datasheet gives 80 % for the fixed 5 V part. The rest is lost in the switch, the diode and the inductor. ## The 5V pin or the barrel jack? Set to 5 V, the module goes on the 5V pin, which skips the Uno’s regulator altogether. Set to 7 to 9 V, it could go into the barrel jack or VIN instead, and the Uno’s regulator would make the last step to 5 V. On a real board that wastes some of what the buck saved, since the regulator burns the last 2 to 4 V as heat. Mokxi’s Uno is always powered by its USB and ignores VIN, so the circuit here shows the 5V pin route only. A buck set to 5 V and a 5 V adapter on its input is not enough: the LM2596 needs about a volt across itself, which the next section shows. ## Reading the adapter on A0 12 V on A0 would wreck the pin, so the 10k and 4.7k bring it down to 4.7 / 14.7 of the adapter: 3.84 V from 12 V, which analogRead gives as 785 of 1023. The sketch undoes the divider and prints the adapter’s volts, so a battery running down shows up in the serial monitor long before the module drops out. Read the adapter through the divider ## Its limits: headroom, current and the input range Headroom. The LM2596 can hold its switch on all the time, so near its input the output follows the input down. Set to 5 V from 5.5 V, it gives about 4.5 V at an amp. For 5 V out, give it 6.5 V or more. Current. The switch limits at 4.5 A peak, about 4.2 A of average output. Ask for more and the output falls instead: half an ohm on a module set to 12 V from 24 V sits at about 2 V. The board is sold as a 3 A converter, and past 3 A a real one runs hot. Input. Under 4.5 V in it is off, and the datasheet’s top is 40 V. Most modules have no reverse protection, so the adapter backwards or into OUT+ kills the chip. What the simulator leaves out: the 150 kHz ripple (the output here is its average, where a real one carries 30 to 60 mV), heat and thermal shutdown, the soft start and the module’s light-load efficiency. ## Questions How do I adjust the LM2596 output voltage? Turn the brass multiturn trimmer with a meter on OUT+ and OUT-, with the input powered and nothing on the output. Set it before connecting a board. In Mokxi it is the module’s volts property. Can I power an Arduino with an LM2596? Yes. Set the module to 5 V and wire OUT+ to the 5V pin and OUT- to GND, or set it to 7 to 9 V and use the barrel jack or VIN. Give the module at least 6.5 V in for 5 V out. What is the LM2596 current limit? The switch limits at 4.5 A peak, about 4.2 A of average output. The module is sold as 3 A, and past that a real one needs cooling. Is an LM2596 better than a 7805? For a big step it is. From 12 V to 5 V at 1 A it takes about half an amp from the adapter, where a 7805 takes the full amp and turns 7 W into heat. A 7805 is quieter and simpler for small loads. What input voltage does the LM2596 need? 4.5 V to 40 V, and about a volt more than the output you set. Below 4.5 V it is off. Related ## Keep going Voltage Dividers and Why They Are Bad Power Supplies Arduino Battery Level Indicator: 18650 on A0 How Many LEDs Can One Arduino Pin Drive? Zener Diode Voltage Regulator Circuit, Simulated Arduino Relay Module: Active LOW and Startup Clicks Help: how the LM2596 is modeled The project: an Arduino on 12 V with an LM2596 Beginner The voltage regulator simulator: a 7805 on a battery The Arduino Uno simulator The project page, with the full sketch Beginner Sources ## Where the facts on this page come from - Texas Instruments: LM2596 datasheet (SNVS124), efficiency, current limit and input range - Arduino: Uno Rev3, its power pins and input voltage ## Build this for real Open the editor, change a value and watch the number move with it. Nothing to install, and no account needed. Start building free Open the editor