Full project name:
OK, ok, You got me. Maybe it is not smaller than this one created by Murata Manufacturing company but definitely something You can build by Yourself in home using commonly accessible elements and tools.
My idea was to create a compact switch mode power supply for my small microcontroller based projects.
This project is also a kind of tutorial how to create paths on a PCB using solid wire instead of build paths with a solder.
Let's do it!
Step 1: Design
You can find many pocket-size power supply custom designs, but most of them I found had 2 biggest disadvantages:
- They are linear power supplies, meaning they are not very efficient,
- They are either not regulated or regulated in steps
My step-up converter is a switch-mode power supply with a smooth regulated output voltage (via regulated resistor). If You want to read more, there is an excellent document on microchip.com which exaplains different architectures, pros and cons of using SMPSs.
As a base IC chip for my switch mode power supply I picked very popular and commonly available chip MC34063. It can be used to build step-down (buck), step-up (boost) converter or voltage inverter just by adding some external elements. Very nice explanation how to design SMPS using MC34063 was done by Dave Jones in His YouTube video. I strongly recommend You to watch it and follow the calculations for values of every element.
If You don't want to do it manually, You can use online calculator for MC34063 to fit Your needs. You can use this one by Madis Kaal or the one designed for higher voltages on changpuak.ch.
I picked elements only roughly sticking to the calculations:
- I picked the biggest capacitors which could fit onto the board. Input and output capacitors are 220µF 16V. I You need higher output voltage or need higher input voltage, pick capacitors which fit.
- Inductor L: 100µH, this was the only one I got with the size of the chip itself.
- I used diode 1N4001 (1A, 50V) Instead of some Shotky diode. The switching frequency of this diode is 15kHz which is less than my switching frequency I used, but somehow the whole circuit works just fine.
- Switching capacitor Ct: 1nF (it gives switching frequency ~26kHz)
- Current protection resistor Rsc: 0.22Ω
- Variable resistor which represents resistance ratio R2 to R1: 20kΩ
- Pick the switching frequency (by choosing proper switching capacitor) in a range of Your diode (by chosing Shotky's diode instead of general purpose one).
- Pick the capacitors with more max voltage than You want to provide as input (input capacitor) or get on the output (output capacitor). E.g. 16V capacitor on the input (with higher capacitance) and 50V capacitor on the output (with less capacitance), but both relatively the same size.
Step 2: Materials and Tools
Materials I used, but exact values stronly depends on Your needs:
- Chip MC34063 (Amazon)
- Switching capacitor: 1nF
- Input capacitor: 16V, 220µF
- Output capacitor: 16V, 220µF (I recommend 50V, 4.7µF)
- Fast switching diode: 1N4001 (Some Shotky diode is much faster)
- Resistor: 180Ω (arbitrary value)
- Resistor: 0.22Ω
- Variable resistor: 0-20kΩ, but You can use 0-50kΩ
- Inductor: 100µH
- Prototype PCB board (BangGood.com)
- Some short cables
- Soldering station (and utilities around it: solder wire, resin if needed, something to clean a tip, etc...)
- Pliers, diagonal pliers/side cutters
- Saw or rotary tool to cut the board
- Duct tape (yes, as a tool, not as material)
Step 3: Placing Elements - Beginning
I spend a lot of time to organize elements on the board in such a configuration, so it occupies as less space as possible. After many tries and failures, this project presents what I ended up with. At this moment, I think this is the most optimal placement of elements using only 1 side of the board.
I was considering putting elements on both sides, but then:
- soldering would be really complicated
- It doesn't actually occupy less space
- SMPS would have some irregular shape, making mounting it into e.g. a bog or on a 9V battery very hard to achieve
To connect nodes I used a technique of using a bare wire, bend it in an expected shape of a path and then solder it to the board. I prefer this technique instead of using a solder, because of:
- Using solder to "connect the dots" on a PCB I consider crazy and somehow inappropriate. Nowadays soldering wire contain a resin which is used to deoxidize the solder and the surface. But using solder as a path builder, makes the resin to vaporize and leaving some oxidized parts exposed, which I consider not so good for the circuit itself.
- On PCB I used, linking 2 "dots" with a solder is just almost impossible. Solder sticks to "dots" without making an intended connection between them. If You use the PCB where "dots" are made out of copper and they are very close to each other, then it looks easier to make a connections.
- Using solder to create paths uses just...to much solder. Using a wire is just less "expensive".
- In case of a mistake, it can be really hard to remove old solder path and replace it with a new one. Using wire-path it is relatively much easier task.
- Using wires makes much more reliable connection.
The disadvantage is that it takes more time to shape the wire and solder it. But if You get some experience it is not hard task anymore. At least I just used to it.
- Main rule to place the elements is to cut the excesive legs on the other side of the board, as close to the board as possible. It will help us later when we will place the wire to build paths.
- Don't use element's legs to create paths. Generally it is a good idea to do it, but if You make a mistake, or Your element needs to be replaced (e.g. it is broken) then it is really hard to do it. You will need to cut the path-wire anyway and because legs are bended, it can be challenging to pull out the element from the board.
- Try to build paths from inside of the circuit to the outside, or from one side to the other. Try to avoid situation, when You need to create a path, but other paths around are already created. It can be hard to hold the path-wire.
- Don't cut the path-wire to the final length/shape before soldering.Take longer path-wire, shape it, use a tape to hold the path-wire in a position on the board, solder it and finally cut it at a desired point (check photos).
Step 4: Placing Elements - Main Task
You just need to follow the schematic and place the element one by one, cutting the excessive legs, solder it as close to the board as possible, shape the path-wire, solder it and cut. Repeat with another element.
- You can check on a photos how I placed every element. Try just to follow the provided scheme. In some complex circuits dealing with high frequencies etc, inductors are placed separated on the board due to magnetic field which can interfere with other elements. But in our project we just don't care about this case. That's why I placed the inductor just directly on top of MC34063 chip and I don't care about any interferencies.
Step 5: Cutting the Board
You need to know before, that PCB boards are really hard and because of this difficult to cut. I tried first to use a rotary tool (photo). The cutting line is very smooth, but it was taking very long to cut it. I decided to switch to a regular saw to cut metal and for me it was working generally ok.
- Cut the board before soldering all elements. First place all the elements (no soldering), mark cutting points, remove all the elements, cut the board and then put elements back and solder them. During the cutting You need to take care of already soldered elements.
- I would prefer to use saw instead of rotary tool, but this is probably an individual thing.
Step 6: Shaping
After cutting, I used a file to smooth the edges and round the corners.
Final size of the board was 2.5cm length, 2cm width and 1.5cm height.
The project in its rough form is done. Time for testing...
Step 7: Testing Operation
I plugged the board to a LED stripe (12 LEDs) which needs 12V power supply. I Set 5V input (privided by USB port) and using regulated resistor I set up 12V output. It works perfectly. Because of the relatively high current drawn, the MC34063 chip was getting warm. I left the circuit with LED stripe on for some minutes and it was stable.
Step 8: Final Result
I consider it as a big success that such a small SMPS can power up this kind of current drawning thing like 12 LEDs.