How do DC adapters work?

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How do DC adapters work
How do DC adapters work?

Even when some people get their head around power adapters, one of the most commonly asked questions is ‘What is the difference between an AC adapter and a DC adapter?’

The answer couldn’t be simpler: There is no difference.

That’s because, in almost all cases, what the power adapter in question is doing is taking the AC power source – for instance, from the mains supply – and translating or ‘adapting’ it to the DC power supply the electronic device in question is asking for.  Remember, AC (alternating current) is used to transmit power from the electrical substation, across the power lines, and to your home or business. 

And why?  Because the multi-directional nature of AC keeps the voltage high during transmit, which reduces the current, minimises wasted energy, and keeps the conversion to the DC power you need a lot simpler and cheaper.

And so, while some may refer to their DC adapters and related DC power connectors because what they do is produce DC power, others call them AC adapters – because they are adapting AC power.  That’s why you’ll often see them referred to as AC/DC adapters, but in essence, they’re all  doing the same thing.

So how does an AC or DC adapter do its thing?

The process of converting AC to DC is called rectification, relying on a circuit within your adapter as the rectifier.  When the AC power is introduced to the circuit, the diodes sort out the multi-directional current so that it can only pass through in a single direction – with the DC power connectors then transmitting that current to your device in its precisely required form.

But before the power can make the device work, it needs to be further translated into a more stable form.  That’s because while the rectifier limits the current to one direction, the voltage continues to ‘pulsate’ in an AC-like manner.  DC circuits, however, do not tolerate this ‘pulsating DC’, so additional filters are added to the mix to knock down the highs and the lows of the pulses.

The DC adapter for your specific operations comes in three basic rectifier forms: half-wave, full-wave and bridge:

Half-wave

This is the simplest form, comprising just one diode.  “Half” refers to the fact that only about 50% of the AC input is converted – the 50% that was already travelling in the required direction.  While simple to manufacture, half-wave adapters are less efficient because for half of the time, the output voltage is precisely zero.

Full-wave

A full-wave rectifier therefore features not one but two diodes, meaning that both directions of travel of the AC input are passed through.  These more sophisticated adapters effectively double the voltage pulse rate of the half-wave version.

Bridge

Finally, bridge rectifiers correct the main problem with the full-wave setup – DC output with half the voltage output from the transformer.  The solution is simple and intuitive: double the diodes (4).  With the four diodes arranged in a diamond shape, two of them deal with blocking current, while the other two allow it to pass.  However, the voltage output from the transformer is fully utilised.

If your business or organisation is on the market for a DC adapter, the easiest way to make your choice is to match the required specifications with the original adapter.  If you don’t have that original, though, adapters differ in terms of the required voltage, current, and the DC power connectors including size and polarity.  Not sure what to do next?  Always consult with an industry expert to match your requirements with the most efficient and cost-effective device for your specific purposes.

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