What Technological Advancements Have Reduced The Size Of Household AC-DC Adapters?

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The reduction in adapter sizes has come about due to significant decrease in the sizes of individual components and simultaneous increase in efficiency. The design of the adapter is also completely changed due to the replacement of bulky transformers with switch based transistors.

Food, clothing and shelter are no longer the only bare essentials needed to survive in this world. In this ever-changing digital landscape, some things have become absolutely mandatory if we want to stay connected to the world at large. Some of these things include an Internet connection, a modern smartphone, a functioning laptop, and a smart TV to play video games (stress relief!), among other things.

However, these things are mere paperweights if you lack the mother of bare essentials—an adapter. Yes, anyone reading this knows that excruciating feeling when you get up in the morning and find that you didn’t plug in the phone charger.

you wake up & the charger wasn't plugged in meme

These pocket-sized devices help us power all the equipment to which we find ourselves addicted, but these charging devices weren’t always this small. They were quite bulky and inefficient, and it took some serious innovation to get where we are today. To understand the advancements needed to reach this size, we first need to understand what they actually do.

The power supply problem

Our current infrastructure is set up to produce electricity through coal, renewable, and hydro-thermal energy sources, among others. These sources are usually far away from the city and power must be transported through grids to individual homes. This transfer is achieved through Alternating Current (AC), as it is the most efficient when traveling long distances. However, our devices need Direct Current (DC) to charge, so the electricity traveling behind our switch sockets, AC, needs to be converted to DC for charging our devices.

This is where an AC to DC adapter takes center stage. Simply speaking, all adapters are basically a circuit through which the incoming AC current is passed, which gets converted into the DC current.

linear power supply circuit illustration

linear power supply circuit illustration

Linear power supply (LPS)

Initially, the conversion was done through a circuit system called a linear power supply (LPS). The incoming AC current is high, around 115V to 230V, which must be brought down to 30V, and then converted to a steady DC voltage. This is done through a steel or iron Transformer, which is the main part of the LPS system. The transformer acts as a barrier to separate high voltage AC input from low voltage DC input, filtering out any noise that may be getting into the output voltage. The AC voltage is then passed through a pair of diodes, which rectifies it and acts as a one-way valve for the current to flow forward.

The voltage then passes through a pair of large electrolytic capacitors, which smooth it into a low DC voltage. A Transistor regulates the voltage as a steady output. The voltage still needs to match the output power requirements of a particular device, which is done through a Voltage Regulator. However, here’s the catch, as the voltage regulator is resisting current to maintain a voltage, it also acts as a power-dissipating device. This results in a constant loss of useful power to maintain the voltage level.

DC Power Supply on white background - Image(Olga Popova)S

Bulky LPS (Photo Credit : Olg Popova/Shutterstock)

There are some pretty major shortcomings of LPS. There is constant heat loss, which needs to be absorbed through a heat sink, adding an unnecessary increase in adapter volume. The transformer itself is also huge in size, which makes the adapter really bulky.

Imagine carrying this monstrosity around to charge your devices… “inconvenient” would be an understatement. Fortunately, as usually happens, necessity drives people to make more functional inventions, so the advancement to smaller adapters occurred.

The advancements to reduce the size of AC-DC adapters:

The first clear advancement of today’s adapters with respect to LPS is the input change being made to switching converters instead of transformers. This changed the overall design completely and this system came to be known as Switch Mode Power Supply (SMPS).

Switch mode power supply circuit illustration

Switch mode power supply circuit illustration

The incoming AC voltage (115V – 230V) is smoothed by a set of diodes and a capacitor that provides high-voltage DC. The voltage is carried to the switching transistor (also known as MOSFET’s), which turns on and off rapidly. This transistor produces chopped DC voltage.

Macro shot of power transistors on the black surface - Image(Andrei Kuzmik)S

A switching transformer, first leap in small adapters(Photo Credit : Andrei Kuzmik/Shutterstock)

The chopped DC voltage is fed to a ferrite transformer, which was another critical innovation, because the size was shrunk to that of a piece of candy. This transformer converts the pulsating DC into high-frequency AC.

Transformers for a switching power supply. - Image( Mykhailo Motov)s

The shrunken transformer size. (Photo Credit : Mykhailo Motov/Shutterstock)

For the final DC output, the high-frequency AC is sent to a second bridge rectifier, which converts it a final time. All the while, a sensing circuit monitors the output voltage, getting feedback and adjusting the duty cycle to maintain a constant voltage output.

Laptop AC adapter on white - Image(Freer)S

A considerable size reduction and compact design (Photo Credit : Freer/Shutterstock)


The adapter is a testament to Moore’s Law, which asserts that the number of transistors in a chip will keep doubling every 18 months due to size shrinkage and increasing computational power. A complete revamp in design for the flow of the voltage was an essential part of the advancement for adapters, as this enabled less dissipation of heat and higher efficiency (85%-90%).

Additionally, all the working parts were shrunk to a more manageable size and became far more efficient. The introduction of switching transistors alone was a huge leap that enabled the elimination of such huge transformers.

So, the next time you plug in an adapter, acknowledge the human drive to make things smaller, better and more efficient that allows you to carry it in your pocket. Also, don’t forget to switch it on before you go to sleep!


  1. Massachusetts Institute Of Technology (Link 1)
  2. Massachusetts Institute Of Technology (Link 2)
  3. ResearchGate
  4. University Of Nevada, Las Vegas
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About the Author:

Vishal is an Architect and a design aficionado. He likes making trippy patterns in his computer. Fascinated by technology’s role in humanity’s evolution, he is constantly thinking about how the future of our species would turn out – sometimes at the peril of what’s currently going on around him.

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