Introduction: Buck Converter (DC-DC)
Alright! So hello everyone! Long time user, follower, commenter but first time iblest here! So for my first instructable I thought I'd share a recent simple project I made; a Buck Converter.
Buck Converters are great! I use them all over the place in many of my nerdy, techy, geeky hobbiest projects. They also can commonly be referred to by other names, a DC-DC converter or a switching regulator. Essentially what it does is take some higher voltage in (higher than what you want for your project), chops it up, and pieces together a lower voltage. It might help to think of it as a transformer for DC circuits... only without the giant iron block... and without the long coils of wire... and with only 3 pins.
Ok ok so it might not be like a transformer electrically speaking but it does take a voltage in and transform it to a lower voltage. It achieves this by taking the higher source voltage and "chops" it. The Buck Converter integrated circuit (IC) switches the higher voltage on and off very very quickly. It then passes this through caps and inductors and filters it down to a desirable lower voltage. Essentially if you increase the "on" time you increase the voltage out and vice versa.
So you may be wondering why use the more complicated Buck Converters when a simple voltage regulator serves the exact same function with no external circuitry. The answer? Buck Converters are WAY more efficient. They achieve their purpose at around 90-95% efficiencies. Regulators get their lower voltage by bleeding off the excess voltage as heat. So if you need 10V from 12V a regulator would probably be just fine and heat worries are probably not a concern. But if you have 16V (from a li-ion battery pack) and need 3.3V (to power various IC's) a regulator would have to bleed off about 13V! That's a lot of voltage to turn to heat! A buck converter solves this problem without the need for big and bulky heat sinks.
So now if you've decided to make a Buck Converter circuit, let's get to it!
Step 1: Gather the Materials!
So with any prototyping project this really shouldn't be the first step... But we're gonna go ahead and do it cuz it's just so darn fun! Just a little disclosure, we'll be using the ACT4088 picked because it's cheap and has an adjustable VOut along with a max of 1.5A out. Of course if you need different characteristics chances are, there's a chip out there for you! The circuit we'll build is taken straight from the IC's datasheet and works very well!
List of parts:
- ACT4088 - http://www.mouser.com/ProductDetail/Active-Semi/AC...
- 4.7 uH Inductor - http://www.mouser.com/ProductDetail/Murata-Electro...
- Schottky Diode - http://www.mouser.com/ProductDetail/Vishay-Semicon...
- 10 uF Capacitor - http://www.mouser.com/ProductDetail/AVX/08053D106K...
- 22 nF Capacitor - http://www.mouser.com/ProductDetail/Vishay-Vitramo...
- 22 uF Capacitor - http://www.mouser.com/ProductDetail/AVX/08056D226M...
- 49.9 kΩ Resistor -http://www.mouser.com/ProductDetail/Vishay-Dale/CR...
- 16.2 kΩ Resistor -http://www.mouser.com/ProductDetail/Vishay-Dale/CR...
Notes: Alright, now to address some design notes.
- All parts are surface mount for two reasons. 1: Our project will take up much less space once completed. 2: SMD parts are generally cheaper nowadays. :P
- The inductor listed is shielded as speced in the datasheet however I got an unshielded one and the circuit works just as well and it's about $0.20 cheaper.
- The two resistors listed are speced for a 3.3V out however you are more than welcomed to change them to whatever values you want! The resistor selection is how you change VOut to whatever is desired. The datasheet recommends keeping the 49.9 kΩ resistor and changing the 16.2 kΩ resistor. This being said with a little imagining you can see how a potentiometer can be used to make your very own $2 variable power supply! Which I have done and will show you at the end of this instructable.
Step 2: Design the Layout
Alright, so now let's design the layout for the circuit we'll be using for the Buck Converter! Don't worry, it's a very simple circuit and we'll be getting the design straight from the datasheet. This is "v1.0" of my design and have thoughts for a "v1.1" I'll share at the end! My goal when designing the layout was to fit it within a 1 square in. board which it does easily!
I use a software called DipTrace. For me it's easy to use and has a very large library to choose parts from! Though if you do have a part that's not listed (as I encountered when placing a WT32 bluetooth module) you can easily add it to the user library. For this circuit even though the ACT4088 doesn't have a part listed it does use a standard footprint layout that is included in the DipTrace library, so that's what I used and it fits perfectly! If you would rather use some other layout program such as EagleCAD or other software you can absolutely use it, I just don't have any project files for any other program besides DipTrace.
Step 3: Order Your Boards!
Alright so now that we have our board layout design let's upload them to a manufacturing company! For this project I used OSH Park. They do a fantastic job and offer some great services at some really great prices! They are particularly suitable for small board orders and they are run out of the US too!. the boards cost me around $1.30 a board and had to order in muliples of 3... so I got 9. lol. Another fantastic feature is that they gold plate all the contacts, pads, and holes making it ideal to solder to and gives the board an excellent finish. Also the dark purple they use for their solder mask is sick looking!
The order took about a week and a half to get to me with no delays, free shipping, and usps so no need to be there to sign! (the signing for packages thing may be one of my soap-boxes that I will save for another time)
Step 4: Solder Parts to the Board
Alright this step may be a bit daunting for some of you as the parts are small and SMD. But don't fear! It really is easier than it looks and I'll share a few tips and tricks to make the job easier.
Soldering Iron: Having the right tool for the job is essential for any project! And if you're an electrical hobbiest this tool is an absolute must! I personally use a soldering station, the Weller WES51. This iron has exchangeable tips and get up to temp in about 10 - 15 seconds. When soldering SMD parts it is extremely important to use an iron with a fine point tip! Though it is possible to use Walmart's $5 big bulky plug-n-play iron, a station with temp control and i fine tip makes a strong, reliable, perfect solder joint every time with ease.
Tweezers: As stated before, get the right tool! Tweezers make life so much easier when working with SMD components. You really can make do with any type, from the ones found at any pharmacy store to the specially designed ones you can order when you order parts at Mouser.com
Clamp: This is optional though having a clamp can greatly help securing the board and keeping it from moving. I did not use one but if you don't you'll need a free finger to hold the board down and with an iron being so close to your finger... beware! I have been burned... many times... and it is not pleasant.
Pre-tinning: One thing that can make all your solder connections more stable and easier to make is to pre-tin any connection you're about to make. For this project we'll apply solder to a single pad on the board. Then take the appropriate part with tweezers, heat up the pad with solder, and tack one side of the part to the pad. Then make a clean solder connection on the other side before cleaning up the tack solder joint. By doing it this way you wont have to hold the solder in addition to the part when you adhere it to the board!
Examine: It is important to examine your board closely when finished! If you see any questionable joint now is the time for patience and diligence. Re-heat the connection and clean it until it meets your requirements. Check for shorts! Thankfully this is a very simple circuit and the only major source for shorts is on the IC itself between the pins. If a short does exist just re-heat the joints and pull away with your iron.
Step 5: Test Your Board
Alright, you've done it! But now... the moment of truth... the scariest part of any electronic project... the dreaded... powering on. We had a saying back in college, "If it works the first time... you did something wrong." Alas though my first attempt at powering on the board was actually successful! I know, I'm worried too. In fact it's been quite some time and I still have worries! :D
Now hook up any ole power supply, preferable 5V or more, to the VIn and GND pins. Then all that's left to do is grab your trusty voltmeter and test from VOut to GND! You should be reading 3.3V. That's it! You're done! Now you can make those complicated projects requiring multiple voltage supplies much more efficiently and let's be honest, it'll look cooler too ;)
Step 6: Thoughts and Suggestions
Now we can evaluate what to do to make this project even better!
- The first adjustment I'd like to make would be to the placement of the VIn, GND, and VOut pins on the board. After showing my design to a friend he recommended placing the pins in a straight line. This would allow you to connect the board straight to your project without the need for jumper wires! you could solder pins from this board to any other board you wanted to add a Buck Converter to! In fact, you could adjust this to be a direct replacement to any through hole voltage regulator!
- The second alteration I would make would be to add a second circuit. See, I found that when I made this circuit it all fit onto a single side of the board. This means that the exact same layout could in theory be duplicated and put on the opposite side of the board! And it even may be possible to do a little tweaking to share the VIn and GND pins too!
- This one is just a thought I'd like to share with others. A few years ago I altered a Buck Converter board very similar to this one. To set the VOut of the IC, fundamentally it simply uses a voltage divider to set a reference pin. Just swap in a potentiometer and voila! Your very own power supply! I fit one into an altoids can... cuz it's cool, and use the potentiometer shaft as a little stand!
Anyways, I hope you enjoyed this project and please feel free to ask any questions or leave any comments below!
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