Paul McGowan writes: A recent post explained a bit about how a switch mode power supply works – it uses a simply electronic switch to chop up the incoming AC into smaller, faster bits so we can use a much smaller power transformer working more efficiently than a giant beast like those you find in a big power amp. To visualize what it’s doing, just imagine turning a light switch on and on hundreds of thousands of times a second and the output of that switch is connected up to this small power transformer. The fast speed is what’s needed to use a small transformer.
One the output side of this power transformer we have the same very fast bursts of energy that we then run through the exact same DC converter circuit and supply capacitors as we would in a larger, conventional supply. The difference here is rather large and it has to do with the size of the power supply capacitors. If you’ve ever looked inside a big amplifier with a conventional power supply, you’ll see huge banks of very large power capacitors. These capacitors store the peak energy the power amplifier needs to deliver its watts to the speaker. The caps are huge because of the frequency of the incoming power – typically 50Hz (times a second) or 60Hz. Just like the transformer, however, the higher the frequency, the smaller the capacitor can become to store the same amount of energy.
So the input switch, which is creating the fast bursts of energy from the AC line, permits us to use exponentially smaller transformers and power supply capacitors to get the same isolation, power throughput and storage as we would in a giant, big and klunky version.
So is that all? Nope, and tomorrow we’ll cover what perhaps the most important aspect of a SMPS is.