Circuit Board

Choosing Fuse for Power Line Input in Embedded System Designs

This is a question that came to my mind as I was designing my power input for a device I am working on. I thought I share my process for choosing a fuse to protect the device and ensure no damages could result from over-current.

I am using a RAC20-05SK as the AC/DC converter from the Neut and Line power inputs to a steady 5V output with 4 Amp and 20 W. The following schematic is the current design as well as further information that were needed to make this decision. By the way, it is always a good idea to write notes on your PCB schematics design.

A 1.5 Amp Fuse would do the job in this design since the input continuous current is 450 mA at 115 VAC. The other important factor that we need to consider is that the inrush current is 20 A at 115 VAC and 40 A at 230 VAC, so we need to place a Time Delay Fuse or Slow Blow, this will give time for the converter to stabilize and return to continuous current at 450 mA.

The next important factor to remember is the rated voltage of the fuse needs to be able to handle the max input AC voltage, in this case it is 264 VAC.

So after looking at the above given information, the best option for my case is a 3 A 250 VAC Fuse SMD and Slow Blow and with a breaking capacity of 50A.

Part # 0443003.DR
Link to DigiKey Part Info

0443003.DR Littelfuse Inc. | F2910CT-ND DigiKey Electronics
Source: DigiKey

Please be cautious when experimenting with high voltage power line input, it could kill you. We are not promoting or suggesting that you follow any of our recommendations without a professional credibility to be able to verify what you are doing.

We are not affiliated or paid by any of the mentioned third-party companies to write this article. We are simply a fan of their products and want to learn more about the future of such products. Nothing on here that we recommend that we would not use ourselves. Please feel free to leave your feedback!

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