Simpler–yes. But cheaper is changing. It used to be that low-power devices all used a heavy iron-core transformers (wall warts), but today they’ve all been replaced with switch-mode power supplies (which use a tiny transformer and some electronics to regulate the voltage). Switch-mode isn’t just more efficient; it’s cheaper, too. Power electronics may be more expensive per unit weight, but the switch-mode supply is much smaller and lighter.
Yes, smaller, lighter, and more efficient. The only problem is that there’s some noise on the DC output, which can cause problems in sensitive analog circuits. I discovered this the hard way.
On the other hand, a normal transformer passes noise from the input to the output, so if you have noisy wall power for whatever reason, they provide less isolation. And they may have more ripple since they have to rectify the AC into DC and the filtering caps aren’t always sized adequately.
The frequency range for the noise on linear PS’s is very low and easily filtered. By contrast, the frequency range for the noise on SMPSs can reach into the MHz due to sharp harmonics, and that crap is hard to filter out.
Last year I ran into all kinds of problems when I powered some 28 V military aircraft hardware using a brand new Kepco laboratory SMPS. Lots of crap in my scope signal when probing the low-level analog portions of the circuit. I tried filtering the 28 V, but it didn’t do any good. Finally ditched the SMPS and used a big ol’ HP “boat anchor” linear power supply made in the 1980s. No more noise in my scope signal when probing the circuit.
A real linear power supply is a somewhat different beast. Transform/rectify to get the output in the ballpark, and then a linear voltage regulator to bring it to the desired range. Very smooth output at the expense of even more efficiency: all the power from the voltage drop goes straight to heat. Hence the giant heatsinks on the supply.
Wall-wart style transformers generally didn’t do that. Transform/rectify, then some caps for filtering. But they can only do so much.
Way back in the day, I was teaching a college physics lab, and on the day that we were doing electromagnetic induction, one of the questions at the end was “Why are there no DC transformers?” One student wrote “Because Marvel got the comic book rights”
And…
What was his grade?
Currently available switchers are pretty low noise. I use amateur shortwave radios and have never really found anything around the house that kicks up RF: TV/audio entertainment gear, home IT stuff like modem, router, computer power supplies, etc. Most of the lighting in the house is CFL or LED of assorted vintage, notorious noisemakers but I don’t hear them on the radio.
My 50 amp 12v linear Astron is nice to have but at about a pound an amp and bristling with sharp pokey heatsink fins, not nice to move. My little radio only uses maybe 10 watts so I’ve got a couple flavors 3A binding post supplies like these below. No nonsense and quiet.
It’s been over a decade, but IIRC, he was a pretty good student. There are two kinds of EE student: Both already know everything about electronics, but some of them are right.
(he also gave the other answer to that question, thereby saving me from the dilemma of whether to give credit)
The definitions of AC and DC are a bit fluid, but within context it is usually pretty clear what is meant. A clue about the problem is that no-one ever uses the full names “Alternating Current” and “Direct Current”, basically because that is way to limiting, and not just because the signal might no be alternating in polarity, but it probably isn’t just current either.
Years ago I was discussing some spectral energy measurements with a physicist from a client company. He pointed the the value at the first plotted wavenumber and said “that’s DC right?” It was indeed the zero’th wavenumber and calling it DC made perfect sense. So much so that I would be happy defining DC that way.
The point about AC and transformers is simply that in order to use magnetics to transfer energy, you need a varying magnetic field to induce a current flow.
Switch mode power supplies as a totally different question. You can divide them into two types. Ones that use a very high frequency drive and a small transformer, and those that just chop the input current and switch it to charge capacitors to the needed voltage. This can get arbitrarily evil.
The point about high frequencies and tiny transformers is important. The limiting factor for how much power a transformer can deliver is saturation of the core. The more magnetic flux we can sweep though the windings the more power we are transferring. So we use a core that has a much greater magnetic permeability than empty space. This is usually some ferromagnetic material - and usually a specific alloy. But there is no such thing as a free lunch, and these core materials eventually saturate, suddenly stopping any more flux to be crammed into the core. This stops the transformer dead in it tracks, and causes all manner of nasty mess on the output, as well as upsetting the input drive as it suddenly see the load vanish. So transformers are limited by the cross sectional area of the core. But if you can sweep the input current faster, you are transferring energy that much faster as well (since the speed the flux is sweeping though the windings is now faster.) So if you increase the frequency of the drive the power you can transfer through a transformer before it saturates increases proportionately. This is the reason aircraft use 400 Hz. Transformers are vastly smaller and lighter for the same power.
So what if we take this to greater extremes? Say we run a transformer at many kilohertz? Until recently this was losing problem because we now need an electronic circuit to create the higher frequency AC from our input. This minimally needs switching transistors to switch the input at the higher frequency, and these are never totally efficient. They don’t turn on or off instantly, and never fully turn on. They dissipate energy whenever they are not fully on or fully off. But advances in semiconductors brought us high speed devices with enough efficiency that switching power supplies became viable. That was a long time ago, but as devices became cheaper and cheaper they swept everything away. So much so that big iron lump power supplies are a thing of the past for most power supply uses. However the output of the tiny transformer in these power supplies as still AC, and at a uselessly high frequency for any use - so it is rectified filtered and regulated (to varying degrees) before leaving the power supply as DC. Crucially, and why a transformer still exists in such power supplies is that they provide galvanic isolation from the input side - which is directly connected to the mains input, and the output side, which is connected to whatever you are running from the power supply.
The other thing we can do with a switched input is to just switch the input onto a capacitor to charge it up, and stop charging it when it reaches a desired voltage. You can make a power supply with a ridiculously small number of components. Typically all you need is a switching device, a diode capacitor and inductor and a bit of control logic. These work really well when they work, and they show no mercy if anything at all goes wrong. So there is some black magic in their design, and real world devices incorporate a lot of protection and are usually driven by a specialist IC. The lack of a transformer means, depending upon use, that they lack some of the intrinsic protection of a transformer version.
We now see ridiculously efficient devices that are as near perfect switches as you could wish for (Gallium Nitride and Silicon Carbide devices especially). So switching power control is the new normal. They are key part of modern EVs viability. We can do all sorts of magic with these devices. Inside an EV the DC from the battery can be turned into whatever drive is needed at the very moment, and also regulate how the battery charges.
In the extreme we can use a stacked switching system to take input power and switch it up though the stack of capacitors to create near arbitrary DC voltages. And do so at very high power capability. The same system in reverse can create AC back out of the very high DC. Which is basically what the very high voltage DC power transmission systems do. Again, no transformers necessary. Key is that there is energy transfer occurring, but it is buffered as the charge in capacitors and switching this charge in and out of the system is how we can change the form of electrical energy.