Before starting you might wonder what LPS and SMPS are standing for?
LPS is Linear Power Supply
SMPS is Switching Mode Power Supply
So let’s go into it.
A debate that is becoming more and more useless. LPSs and SMPSs are sharing the space in a lot of workshops. In my workshop there are lots of different power supplies, both LPSs and SMPSs ind various sizes.
LPSs are the older ones, but unfortunately the ones with the worse efficiency. They are throwing a lot of power out the window and need big heatsinks to dissipate all that power. LPSs are using a transistor, which will vary its ouwn voltage in order to maintain a stable output voltage. Even though the transistors are big power transistors, they dissipate a lot of power if there is sufficient current going through them. Matters get worse if the output voltage is small.
The upside to it: the output voltage is very clean and rarely has some noise on it. Thats why they are good for microcontrollers since the voltage doesn’t vary at all. Also they are built with few parts. In its easiest form you need a resistor, a transistor and a Z-diode, e voila your LPS is ready for use.
Furthermore they can only regulate an output voltage smaller than the input voltage. (Sounds obvious, but wait a little 😉 ). LPSs are still spread all over the place, espacially the 78xx- and 79xx- regulators are on lots of PCBs.
SMPSs are comparable new to the market, but there are a lot of different variants using nearly the same mechanic behind them. An inductor functions as a current source, while a capacitor is the voltage source (not really that easy, but you get the idea). Depending on how they are wired they resemble a different function. You can build step-down converters (bigger input voltage, smaller output voltage), as well as step-up converters (smaller input voltage, bigger output voltage). Depending on the size of the inductor, you can draw more a bit more current than your tranformer is officially made for, because the current is swithed on and off really fast. however I would not recommend it for step-up converters… They draw a lot more… However, you can only draw litte current from step-up converters compared to step-downs. The bright side: the efficiency can go to 90% and more, even though ~80% are common.
Depending on the SMPS you build, the parts count can go pretty high, needing a lot of special parts like high frequency transformers. But easier SMPSs are buildable with ten or less parts. Also there are lots of integrated switching controllers designed for this use in order to keep it simple.
The downside is that SMPSs are adding noise to the output voltge due to the clocking of them. That’s why a lot of SMPSs are giving you informations like Vrms or Vpp. This is the ripple left behind on the output voltage and should be as small as possible. Because of the complexity of SMPSs they are usually built as high power power supplies. For small power a LPS might do the job just as well.
I said that i have both and I am building both in my projects since they all have their pros and cons. If I need more than 1A, I mostly just build a small SMPS, for less I just use the LPSs (Also depending on power dissipation). If someone is using only LPSs or only SMPSs they might have their reason, but both are useful in different applications. This is a debate without any legitimate reason for dispute…