Ye Good Ole 7805
I use lots of 7805 linear regulators in automotive projects. They usually have a capacity of 1A (in TO-220 package), but even at 150-200mA they generate a lot of heat. Doing the math confirms that this is normal and expected, but it gets to be difficult keeping them cool at times and for this reason, I usually use metal enclosures which become a heatsink. Other than that, they are great.The Switching 7805
Switching regulators are a great solution to heat problem of linear regulators, but take more PCB space. I've seen a couple switching regulator circuits that claim to be drop-in replacements for the 7805, but as soon as I looked at the actual datasheets I realized that they were not -- apparently they don't have space/budget for filtering caps, so they state that these need to be added externally. Yes, I know that 7805's need external caps, but usually just 0.1uf caps that are small and low cost. A lot different that the larger low-ESR caps that switching regulators require. Deceptive advertising IMHO.I decided to see if I could create a true drop-in replacement for the 7805, but which is actually a switching regulator. This would be successful if I could drop in my switching regulator into the 3 holes for a 7805 on most any circuit board. Also, I did not need a full amp, so for my purposes I would allow myself to be successful with a lower-current version. Cost would definitely be higher, but let's see what we can do.
Circuit Design
Although I can design basic buck switching regulators, I am not a guru on this subject. But I don't need to be, as National Semiconductor has a very nice switching-regulator design tool on their website, which has served me very well in the past. I entered my specs and it gives me options for chips (made by National) which can serve the purpose and designs the circuit around those chips. After several designs, a lot of evaluation around physical circuit size, cost, current output, parts availability, etc, I chose a circuit around the LM2674 chip, in 8-SOIC package. This particular circuit would give me just under 0.5A output capability.Implementation
At this point, I laid out the circuit and built it. It works great, and I've used it successfully in a couple circuits. Total cost of around $7 in 1-piece quantities makes it bearable for one-offs, but pricing at 500-1000 pieces is still in the $4 range, so it's still 10x the price of a 7805, and I have not been convinced to use it production yet.Improvements
There's a lot more that I can do to improve this design in terms of cost, space and current output capability. Integrated switchers are still a relatively new technology so smaller and more powerful chips are being released very frequently now. And with all these chips from many manufacturers comes competition, which come to us in the form of better pricing. There are also other options I can use such as tantalum caps, which can also be smaller as higher-frequency switchers get more popular. As soon as I find some spare time...
This last photo shows my usual breadboard 5V PS, which I've been using for ages.
