So most of the projects I have designed recently have all been powered using a wall adaptor or some sort of outlet. Since that was the case I never was concerned about voltage regulator efficiency so I mostly have been using linear regulators like LM7805 of LM317. I opted for these because of their simplicity.
However my latest project I've been working on is battery powered so I wanted to have a regulator that didn't waste a bunch of energy on heat like the linear regs do. This got me thinking that I need to have a "goto" switching regulator in my inventory of parts. I started my search for a switching regular with the following requirements in mind: must be cheap, have a common ground, have a large adjustable range, and must be simple. This led me to choose the LM2596 step down power module. I found these on Ebay for only a couple dollars each so I bought 10 of them.
*note C1 and L1 values in schematic are incorrect. There is also an empty resistor pad underneath the potentiometer.
The reason I wanted them to have a common ground is because for some of my recent microcontroller projects I have designed the pcb in a way where it can be used for other future designs. That way I could re-purpose the extra pcbs I've ordered so I wanted to be able to insert the switching regulator in place of the linear and have it still work. I also wanted to have them be adjustable. The spec that was given when I bought them said it would work from 1.23V to 30V so I figured that would be useable for most of my projects. Lastly, I wanted it to be simple so having all the necessary parts on one board was ideal.
I just got them today and did a quick comparison to my usual linear regulators and am quite happy with their performance so far. With a .5A draw on the output of a 5VDC LM7805 linear regulator I was putting in 12VDC and drawing .510A. This gave me an efficiency of 41%. When I tested the LM2596 I had the same output power draw, except the input had far less current which was around .27A. This means the efficiency of the switching regulator is around 77% which is much better therefore a much lower drain on the battery.
The disadvantage though is the noise. Switching regulators are notoriously noisy so precautions must be taken to filter it out if the noise is a problem. Below you can see the noise on the regulated 5 volt output from the LM7805. It's merely 1.94 mV pk.
If you compare the linear output noise to the switching regulator noise you can see there is a difference of around 34mV pk. The switching frequency is evident on the regulated output from the switching regulator as seen below.
One other thing I noticed was that the switching frequency I was measuring was around 50KHz. The data sheet for the LM2596 states that the switching frequency should be 150KHz so its most likely that that that the regulator on the boards I bought is fake which explains why it is so cheap. A quick search on the eevblog forum revealed that these fake ones don't perform as well as a genuine LM2596. The Ebay seller states it can perform at 90% efficiency delivering 15W of power, but I've been told its only capable of 10W when tested. For its price though, this little module does exactly what I need it to do. If I ever need better performance I will spend the extra money and get a genuine part.
Since the project I am currently on will be using 3 different regulators, I want to make sure I am using the battery power as efficiently as possible. The noise also won't be an issue as well but that is something I will have to keep in mind when using it in the future. As stated before, although my PCB design is already done I can easily insert the switching regulator. I'm glad I found something that is cheap and works well.
I found out that another reason why this module is so cheap is because the LM2596 is outdated. A newer module XM1584 which works up to 3A has an operating frequency of 1 Mhz would be a better option. This means the noise is less of a problem.