Why do some electronics use A/C power, while others use D/C?

I am a pilot learning the electrical system of a complex jet. The aircraft has two different electrical systems, and A/C system, and a D/C system. I understand the inherent differences between A/C and D/C power, however when I started to think of why some devices use A/C power, and why others use D/C power, I realized that I don't know why.





Why is it that some electronic devices use A/C power, while others use D/C power? What is the benefit of using one over the other?

Why do some electronics use A/C power, while others use D/C?
Power distribution can be done most efficiently with three phase AC. Without going into details it simply takes fewer pounds of copper. Unlike ground based systems aircraft generally use 400 Hz AC. The higher frequency results in smaller lighter transformers and smaller lighter actuators (servo motors). This is because one can get the same magnetic flux with less iron at a higher frequency!





Motors and lighting systems can be made to run from AC. Electronic circuits for communications, navigation and instrumentation typically requires DC. In general electronic equipment (apart from the power electronic devices used to control AC) requires a steady time invariant voltage source (DC). Fewer transformers would be required if DC power is distributed to the instrumentation. It would be possible for each instrument to have it’s own DC supply which could be supplied with AC power to be converted but it would be more efficient in many cases to use fewer DC supplies and have the DC distributed. The electronics needs a supply with a constant voltage to function.





Note in a similar way your PC at home is supplied with 120 VAC but the power supply in the computer converts that AC voltage to a number of DC values for the electronics (typically 3.3, +5, -5, +12 and –12).
Reply:Hi Jason,


The short answer is - there are lots of reasons. One of the biggest reasons AC is available on the aircraft is that the generators produce AC. Most all the avionics and nav equipment uses DC, many of the electric motors use AC.
Reply:electronics needs DC power (for expert: except power electronics). Some electronic devices which work on AC voltage, has a built-in converter. the rest devices ,which work on DC voltage, needs an external transformer (AC to DC converter) to get it work.





the difference is some devices has a built-in converter, and other does not have.

sp