3.3V DC-DC Boost Regulator
In case the title of this post didn’t give it away, this is a board that takes a low supply voltage, boost it up, and then regulate it back down to the correct voltage. In this case, 3.3V.
This board is meant to power an RGB LED matrix display that I’m working on. The input voltage will be coming from a pair of AA batteries.
The main component is an SP6641 by Exar Corporation. I got this from Farnell and it packs quite a punch for a decent size and price. The specs claim that this chip can output up to 500mA.
I haven’t put the load capability to the test yet, but the output voltage level is extremely stable at 3.2V. I know what some might be thinking, it’s not 3.3V. But that’s only a 0.1V difference and is well within the tolerances. But having said that, I’ve only loaded it with a 1kΩ resistor and measured the voltage with a standard multimeter. I have no idea how it will perform under fluctuating load. I will eventually hook it up to an oscilloscope to see how it performs when I find the time.
The yellow components are tantalum capacitors for those who don’t know. I had to use two in parallel because it was recommended that the filtering capacitors be of low electrical-series-resistance (ESR). Low ESR capacitors at the capacitance value needed was hard to find and also expensive. My solution was to have parallel capacitors to half the ESR and double the capacitance.
The bottom right component is a ferrite bead. It helps to filter out high frequency noise. Hack A Day has an article on this component.
The component that has 5 leads is obviously the SP6641 and the component right below it is a schottky diode.
The big round component on the far left is an inductor. You’d think that the hardest component to solder is the SP6641 because of how small it is. But, it was actually the inductor. Because the pads for the inductor were so big, it was hard to get solder to melt and flow around and under the inductor. It took a lot of flux and I had to crank up the temperature of my soldering iron. In my opinion, the solder joint doesn’t look as good in real life than it does in the pictures. Oh, and those ‘v’ marks on the top and bottom were supposed to be alignment aids, and my alignment was still off!! Sigh…..
Not visible in the pictures are four standard male header pins. I will be replacing these with low profile ones later on. Why you ask? Well… I like modularity, and while I made this board to power the LED matrix, I want to be able to use it for other projects in the future. I want it to take up as little space as possible, not just laterally. It would’ve been fine if the inductor wasn’t so freaking huge (relative to the other components on the board). Low profile headers are quite pricey, but to me it will be worth it.