What's the difference between an inverter and a converter?

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Knowing the difference between an inverter, converter, transformer and rectifier is essential when designing for specific power supply inputs and outputs. Here's a quick comparison video outlining the functions of each to help clear up any confusion.

 

What is an inverter?

Inverters ultimately have only one job – take in DC current and turn it into AC current. In theory, this is very easy, because a simple switch and some creative wiring can give you an alternating square wave operating at the frequency that you flip the switch.

But in reality, square waves are very damaging to nearly all modern electronics that rely on AC power. So the real question is: How do you take AC power and turn it into something useable? The answer is, you can filter the square wave using precisely selected inductors and capacitors to create a sine wave, or at least something close to a sine wave. 

Oftentimes, inverters will also feature a transformer. This is done so that the AC voltage out can actually be different from the DC voltage in, depending on the number of coils on the primary and secondary winding. 

There two common types of inverters:

  • Pure Sine Wave Inverter (PSW) – The output of a pure sine wave inverter is, you guessed it, a pure sine wave. It is very difficult to achieve a perfect sine wave as an output, and the designs to do so can be very complex.
  • Modified Sine Wave Inverter (MSW) – These can use thyristors, diodes and other passives that produce a rounded-off square wave, and they actually get very close to outputting a pure sine wave. Oftentimes, MSWs can be used for high power electromechanical equipment.

What is a converter?

Converters also have only job: convert AC power to DC power. But the word “converter” is very generic, and you may often see it being used incorrectly. For example, if someone says “DC to AC converter,” that makes logical sense even though the correct terminology is “DC to AC inverter.” The same argument can be made by saying “DC to DC converters.” AC to DC converters are also regularly referred to as power supplies.

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There are two common types of converters:

Half-wave rectifier – These are generally only used in low-power applications because their signal is not very uniform by nature. Since half of the AC signal is lost, the output amplitude is roughly 45% of the input amplitude, meaning that power is heavily wasted during the negative half-cycle of the input. Even when putting a large capacitor over the load, there is still an excessive ripple during the down cycle of the AC input.

Full-wave rectifier – Design engineers use a full-wave rectifier to combat this signal loss and to get a much cleaner signal. They capture both positive and negative cycles of the AC source and are used for applications that need a steady and smooth DC voltage source.

For additional reading, learn how to convert AC to DC using half-wave and full-wave rectifiers.

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You’ll usually see a full-wave rectifier circuit designed in one of two ways: The first utilizes a multiple winding transformer that creates a purely positive signal and can then be smoothed out with a capacitor over the load. The second is called a full-wave bridge rectifier, which effectively does the same thing as the transformer full-wave rectifier but it is a smaller configuration because there is no transformer involved. Either choice is essentially the same strategy as the half-wave rectifier except that there is double the frequency of the AC input and the input nearly never reaches zero.

So you can see how rectifiers and transformers make up parts of the greater converter vs. inverter conversation. Hopefully this video will help you choose the right part for your design.

 

 

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