Introduction: World's Simplest DC Current Limiter

By Thanh Chelseabun
About: I am thankful for all of those who don't do anything at all. It’s because of them I do it myself. And I gonna do it my own way. The lazy way: think easy, do lazy.

Greeting. My hobby is electrical, I'm an amateur electrician and also a DIYer. Today I will make a DC current limiter.

Recently, I designing a bench lab power supply and I need a current limiter to avoid overload. I also want a current limiter to play with other things like motor, etc...

As a lazy people, I always looking for easy, simple, and cheap solution. I had been search for some idea on the internet but couldn't found ones (surprisingly not a single one on Instructables). Original idea is using LM317 IC as current limiter but it's not work as I expected. Other things are complicated. After that, I came up with my idea and it really simple: using a MOSFET.

Enough chit chat, let's back to work.

Step 1: Gather Things You Need

Everythings you need are:

- A piece of perf board (I marked the real size of perf board which needed) - 0.23$ for that full size perfboard

- A ruler

- A knife

- A MOSFET (I use IC 06N03LA which I recycle from an old computer) - 0.18$

- Soldering wire and a solder (I forgot to take a photo)

- A pair of crocodile clip (Red and black) - 0.05$

- A potentiometer. I choose 1k ohm but any potentiometer will work too. I recommend using a multi-turn potentiometer for better controlling current -0.05$

- A 9v battery clip and a 9v battery (You can use the voltage souce to limit itself if the current limiter in power supply) - 0.41$

- 2 wires with diffirent color

- An enclosure that fits the project if you have

- And some basic knowledge

Total cost : 0.87$ < 1$ :D

Step 2: Learn Some Basic

To understand how this instrument work, you have to understand how MOSFET work. For N channel MOSFET, if we apply a voltage between gate (positive voltage) and drain/source pin (negavetive voltage), the current will start to flow from drain to source. Normally, to control the current down to absolute zero, the voltage will be applied between gate and source. Very simple, effective and long life for battery (it takes only 7mA to work, about a LED). Transistor also work similar like this but I don't use transistor because the transistor work if we apply current to it. This current cause lots of heat produced by potentiomter and it drain out your battery very quickly. Mosfet also designed with some others advantage, including allow higher current to pass (06N03LA IC allow up to 50A continuosly).

Step 3: Start to Build

Note: read carefully step by step. Read all step beforce attemp to build

- First, cut the perf board to its size 2.5x5 cm

- Place the potentiometer in a good position and bend its legs

- Put the battery clip's wire into leg 1 and 3 of potentiometer's holes then solder it. Watch the color of the wire. We want higher voltage to the right so positive wire to pin 3 of the potentiometer

- Place the IC into posision and solder the tab first. Pin 1 and pin 3 must stay on a copper mark after solder. Tips: apply heat to the tab for 2 seconds that quickly add solder to the part between perf board and IC's tab. Avoid damaging the IC. Blow some cool air to the IC right after soldering

- Connect gate to pin 2 of the potentiometer, source to pin 1. Use 2 different color wires: black for negative, white for positive

- Solder 2 wires to alligator clips. The length of wire shouldn't longer than 20 cm

- Solder 2 ends of that to source and drain pin. Red alligator clip connect with drain, black with source

Step 4: Final Step: Testing

Connect the current limiter in series between the component that you wish to limit its current and the voltage source. If red clip is connected to posive terminal, the black clip must connected to Vcc of the component. Check before apply some voltage. The photo show I dimming a 3W LED with a current limter. This instrument can be used in many application like power supply, dimmer circuit, ... I recommend you make one to have on your workbench

This is my first instructable and I hope it's helpful for you. Share what you think in comment, add to collection, build this and show it to me. I like to see them all. I'll be back with my next project: build the simplest short circuit protector with current limiter. Thanks for reading.

Cheer!