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Friday, March 11, 2011

Update: Switch Mode Power Supply

Well, I'm back after a fairly long time away from my blog and, unfortunately, away from my projects as well.

Since I last posted, I've have a few developments on the SMPS front, including another excellent source for simple switch mode power supplies at very cheap cost.  If you remember my last post about SMPS, I created a power supply for my baseball scoreboard project out of a car charger for a long defunct cell phone of mine.  A little tweaking to change the output voltage to suit my needs and, presto!  A "reasonably efficient" SMPS.  Here's a link to that post:

Building Blocks: Switch Mode Power Supply

I've had some developments in this arena and I thought I would share it with my fans.

First, back in August of 2010, I was featured on Hack-a-Day, which was really cool.  Mike was a very nice guy and it was really nice to get a little exposure.  For the article, I drew a quick schematic of the power supply, so that might be handy for those that are interested.  Also, I was able to grab my loupe and identify the chip that was being used.  It's an MC34063 switching regulator; apparently quite cheap and quite common to find in a very low end, low cost SMPS.

Shortly after this feature, Dave, from the EEV Blog (one of the few blogs I view religiously, btw) did a video on this exact same voltage regulator and how to run all the calculations.  While I'd like to say that I inspired Dave to do this video, I can't really say that he'd be at all interested in my ramblings, but it was extremely timely and several orders of magnitude more informative than my simple hack, so, good on ya, Dave!

Now, being an unprofessional hack rather than a professional designer, I thought I could do better.  I mean, that SMPS is all through hole parts!  Well, quite a while ago I stumbled upon this quirky, but very inspiring Chinese website called Deal Extreme.  Some people love them, some people hate them, but no one disputes that they sell really cheap stuff.  Combine that with free shipping on everything and you've got a hacker's paradise (assuming you don't sweat the lack of quality of many of their parts).  Digging through their sub$2 parts, I found this gem for $2, which reminded me of my SMPS project.

A couple months later, I finally got my shipment of three of these guys (they were on backorder for a bit).  When I popped open one of them, I found a nice, neat, and extremely small (1"x0.5") SMD based SMPS using the MC34063 regulator.  The resistors appear to be 0603 size, but I was able to change out the resistor divider (similar to my first post about SMPS) with an 0805 size.  So, for $2 I was able to reduce the size of my previous SMPS by 4 or 5 fold.  Excellent!!

Don't mind the wires, those are the ones I tacked on for easy access to the supply voltage and output voltage.

What I also found was a little disturbing.  I have yet to find a fuse in this product, so buyer beware.  I would never use this in any of my vehicles (the most expensive things I own second only to my house, which would also be in danger).  I know my 12V sockets on my car are also fused, but still...  Perhaps it's the principle of the matter.

That being said, I would totally use this to power my creations, so that's what I'm going to do.