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How to choose the right power supply?

June 28, 2019 article

As we build more and more circuits, and all of these circuits have to be powered, we have to ask ourselves: what is the best way to power an electronic circuit? With a power supply, of course. But there are many choices. In this article we will go through the major options out there and list their advantages and disadvantages.

For a beginner in electronics it can be a bit challenging to navigate in the world of power supplies. I know that when I started to think about power supplies I was quickly discouraged. If you are thinking of getting into electronics, then this article is for you :)

This article is organized as a list of six possible power supply solutions, ranging from budget-oriented all the way to high-end. This means that as you keep reading, the power supplies will be more expensive but also offer more options. For each power supply I will also list advantages and disadvantages to let you make an informed decision.

This article is not to be understood as a self-contained introduction into the basics of all power supplies, but please let me know if there is something you want to learn about, and I am happy to cover it in an upcoming article :) If you just cannot wait, have a look at the resources to this article, where I included some external links to more detailed explanatory articles and videos.

As always, please let me know if there are any open questions, or if I forgot something important. You can get ahold of me quite easily on social media, see the box below.

Batteries ($)

Often overlooked, batteries can be a great power source especially for beginners. Together with the right battery holder you have your own tiny power supply. Some of the battery holders even come with an ON/OFF switch, which can be very convenient.

  • safe
  • portable
  • cheap
  • environmentally friendly if you use rechargeable batteries
  • combine batteries (of the same type!) to increase current and voltage
  • fixed voltage
  • limited capacity
  • many batteries needed for high currents

USB breadboard power adapter ($)

Strictly speaking, a USB breadboard power adapter is not a power supply on its own, it is merely a part of it: it still requires you to plug in a USB cable or an AC adapter (see below). However, for breadboard projects (such as the blink LED or the electronic dice these modules work quite well, as long as they don't require too much power.

  • regulated voltage (3.3V or 5V))
  • small
  • portable
  • cheap
  • strictly speaking not a power supply, still needs external USB cable or AC adapter (see below)
  • current is limited to around 1A, not suitable for larger projects

AC adapter ($-$$)

Sometimes I feel that AC adapters are the bane of my existence. Each and every electronic gadget these days seems to come with an adapter on its own. But that can also be a good thing! Many of those AC adapters have useful output DC voltages (5V, 9V, 12V), and some of them are even adjustable. Not all of the AC adapters are regulated, though. If you are building projects with microcontrollers or logic ICs, voltage regulation is very important, so make sure your AC adapter is regulated.

  • regulated versions are available
  • portable
  • not very expensive
  • can deliver substantial power (up to several amperes, depending on the model)
  • comes with many power adapter plugs, which can be useful
  • many poor quality AC adapters out there, be careful what you pick
  • most of them are switch mode power supplies, which means that power can be quite noisy and not very clean
  • not all of them are regulated

Fixed voltage power supply ($$-$$$)

There are many fixed power supplies like the one pictured above, and most of the time they supply around 13.8V. You can hook up your own voltage regulator circuit in the form of an LM7805, LM7809, or LM317 regulator, but it is a bit cumbersome, especially since these units are more expensive than an AC adapter. The only advantage they really bring (typically) is short-circuit protection. I personally do not recommend getting on of these.

  • affordable
  • regulated voltage, typically 13.8V
  • typically short-circuit protected
  • typically come with a dedicated fuse
  • only one voltage
  • heavy and bulky
  • can get very warm at the back side (this is where the power transistor is located)

Switched lab power supply ($$-$$$)

Switched power supplies, also called switch mode power supplies, are lightweight and can be rather affordable, starting around $80. You can see a very generic model above, and there are dozens just like that one on Amazon. They allow you to adjust the voltage (typically in the range of 0-30V DC) as well as the current (typically from 0-2A) for one channel. They are indeed quite versatile.

They work by rapidly switching a voltage on and off, and that voltage gets passed on to an inductor (the yellow things in the image above), that then creates the desired voltage as an output. The switching frequency is typically around a few kilohertz, but especially in cheaper versions of these power supplies it can be in the audible range in the form of a low-key humming.

Perhaps more importantly, the output voltage of the cheaper versions is regulated, of course, but there can be small ripples on that voltage output and these ripples can confuse microcontroller and logic circuits. So if you are working with sensitive circuits, avoid the cheapest ones.

There are also other details to consider: a decent switched power supply costs around $150-$200. For that price you can already get an OK linear power supply which is in many ways superior. Also, and that is quite important, any power supply that does not use a transformer is not galvanically isolated from the line voltage (which can be a safety risk).

Lastly, there are some switched power supplies that have more than one channel. These channels typically always share the same ground potential, which means that you cannot connect the channels in series (to increase the voltage) or in parallel (to increase the current). This is called tracking and it is typically not possible with switched power supplies.

  • small and light
  • affordable
  • regulated voltage and current
  • adjustable
  • quite efficient (>80%)
  • wide range of voltage and current
  • short-circuit protection
  • power can be quite noisy (both electrically and acoustically)
  • no galvanic isolation
  • typically channels are not independent
  • not very future-proof

Linear lab power supply ($$$-$$$$)

Linear power supplies are the gold standard because they offer the cleanest possible output. They use a large transformer, which is why they are rather heavy and more expensive, and linear regulators to regulate the voltage (and hence the name). If you want to see the inside of the linear power supply in the image above, there is a link to Dave's EEVblog with many details on the Korad KA3305P linear power supply.

First off, the output voltage is typically galvanically isolated from the mains voltage. This is great. Also, the main channels of a linear power supply are typically isolated from each other. This means that they can be connected in parallel or in series to increase the current or the voltage, respectively.

Linear regulators, roughly speaking, work like this: say the unregulated voltage, before the regulator, is 30V. But you want 12V. A linear regulator takes these 30V and spits out 12V. It does that by burning the difference (here, it is 30V-12V=18V) in form of heat. This is why linear power supplies are not always very efficient and can get rather warm. All of them have a fan installed, and sometimes this fan can be obnociously loud. If that sort of thing annoys you, make sure to read the reviews before buying one.

If you have the money to spend and are serious about learning electronics, I always recommend getting a linear power supply. The prices start around $150. It is a lot more expensive than a switched power supply, true, but I think that the benefits are quite substantial. If you want to see the inner workings

  • regulated voltage and current
  • adjustable
  • very clean power
  • wide range of voltage and current
  • short-circuit protection
  • galvanic isolation from outlet
  • typically galvanic isolation between channels
  • can connect outputs in series or parallel (tracking)
  • can be used at a professional level in a lab
  • large and heavy
  • can be expensive
  • not very efficient
  • active cooling required, fan can be noisy

The bottom line

I hope I could give you a glimpse into the fascinating world of power supplies. There is much to consider, and it is always a good thing to ask friends, colleagues, or other people in the community for their advice when you are not sure what is best for you.

But I want to close by saying something entirely different. Power supplies are just tools. They are supposed to help us to build interesting circuits and cool projects. In my opinion they should not always be the center of our attention.

I guess what I want to say is this: once you figured out what power supply you want to use, you can focus on the projects you want to build with the help of it :)

Thanks for reading, and please let me know on social media if there is anything in this article that you think is blatantly wrong or needs more explanation. I will do my best!

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  • power supply
  • linear power supply
  • switch mode power supply
  • voltage regulator
  • current regulator
  • galvanic isolation
  • short-circuit protection