The Humble Power Supply

Used every day in schools… and quietly doing electrical wizardry.

If you’ve ever walked into a science lab, a DT room, an ICT suite, or (let’s be honest) a cupboard labelled “DO NOT TOUCH” and found a tangle of mysterious black bricks, you’ve met the humble power supply. It’s the unsung hero of school life: powering microscopes, sensors, laptop trolleys, data loggers, routers, projectors, LED strips, chargers, and that one device nobody remembers owning but everyone is afraid to unplug.

And yet… it’s also a technical marvel. A power supply is basically a small, polite machine whose full-time job is to take whatever electricity it’s given (often rather wild and “mains-y”) and turn it into something calm, safe, and useful for delicate electronics. It does this all day, every day, without applause.

1) The problem: mains electricity is not what your gadgets want

In the UK, mains is about 230 V AC at 50 Hz. That’s brilliant for transmitting power around the country, but it’s not what your Arduino, laptop, or PASCO sensor dreams of at night. Most school kit wants something like 5 V, 9 V, 12 V, 19 V DC, and it wants it stable, smooth, and reliable.

So the power supply acts like a translator:

• Mains AC → low voltage DC

• “Noisy” → “smooth”

• “potentially lethal” → “safe enough to poke into a classroom device without writing a risk assessment the length of War and Peace”

2) The classic approach: transformer power supplies (the chunky ones)

Old-school power supplies often used a transformer. These are the heavier ones that feel like they contain a small neutron star.

A transformer works on electromagnetic induction:

• It takes high-voltage AC and steps it down to lower-voltage AC.

• It’s robust, simple, and often beautifully over-engineered.

Then the power supply has to convert that AC into DC. That typically means:

• Rectification (usually a diode bridge): flips the negative half of the AC wave so it all goes “one way”.

• Smoothing (big capacitors): fills in the dips so you don’t get a lumpy output.

• Regulation (a regulator circuit): keeps the output steady even if the input or load changes.

The result: usable DC… and a box that could be used as a doorstop in a storm.

3) The modern approach: switch-mode power supplies (the clever ones)

Most of today’s “black bricks” are switch-mode power supplies (SMPS). They’re lighter, smaller, and more efficient — which is why you can have a laptop charger that doesn’t weigh the same as the laptop.

Instead of stepping down 50 Hz AC directly, a switch-mode supply:

1. Rectifies the mains to DC first.

2. Chops it at a very high frequency (thousands to millions of times per second).

3. Uses a much smaller transformer at that high frequency.

4. Then rectifies and regulates again to get a clean DC output.

That “chopping” is why switch-mode supplies can sometimes cause electrical noise (and why some audio kit gets grumpy when you use a cheap charger).

4) Why schools absolutely depend on them

Schools are basically power-supply ecosystems. Every department has its own habitat:

• Science: sensors, microscopes, data loggers, centrifuges, magnetic stirrers

• DT: soldering stations, small CNC/laser kit, fans, controllers

• ICT: laptop charging, networking kit, servers, monitors

• Music: keyboards, amps, interfaces, mixers

• Admin: printers, label makers, phones, “conference speaker thingies”

And the secret truth: half the time, the lesson doesn’t fail because the kit is broken… it fails because someone brought the wrong adapter and is now trying to persuade a 12 V device to run on 19 V “because it fits”.

5) The label that saves lives (and lessons)

If you remember one thing, let it be this: read the label.

A power supply label tells you the important stuff:

• Output voltage (V): must match what the device wants.

• Output current (A or mA): the supply must be able to provide at least what the device needs.

• Polarity (centre-positive / centre-negative): crucial for barrel connectors.

• AC or DC output: yes, some supplies output AC. Yes, it catches people out.

A common school tragedy:

• “It turns on and then goes off.” → current too low, supply overheats or voltage sags.

• “It worked once and now smells funny.” → wrong voltage (or wrong polarity).

6) A tiny physics lesson hiding in plain sight

Power supplies are a brilliant real-world link across the curriculum:

• Physics: AC vs DC, transformers, diodes, capacitors, power, efficiency

• Computing: stable supply rails, noise, data errors, brownouts

• Design & Technology: power requirements, safety, connectors, standards

• Maths: P = IV, unit conversions, peak vs RMS, energy and efficiency

And they’re also a wonderful reminder that engineering is often about making something complicated look boring.

7) The power supply deserves a bit of respect

We don’t notice power supplies when they work — which is most of the time — but they’re doing constant, precise, high-speed control to protect your devices from spikes, dips, overloads, and the chaos of the mains. They’re not just “chargers”. They’re small power stations with manners.

So next time you see that pile of identical-looking black rectangles in the prep room, take a moment. Somewhere inside each one is a whole chain of clever ideas — quietly turning raw electricity into something your classroom can actually use.

And if you’re the one in charge of the cupboard of adapters… may your labels be clear, your voltages correct, and your spares box forever blessed.