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Why not use a potential divider in power adaptor? Answered

I thought I could put a bridge rectifier directly after the mains and then pass this through two high value and high(ish) wattage of resistor to act as a potential divider and bring it down to 5v. Why would this not be possible?

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steveastrouk

4 years ago

Because you have no isolation from the mains. Your 5V will be superimposed on the mains voltage, from the point of view of ground.

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mpilchfamily

4 years ago

It would be possible if you are looking to also build a 1500W heater and don't mind that the adapter would be pulling so much power. Cause that is what those resistors will have to dissipate (assuming US mains power). Which would call for some massive wire wound resistors. Which would cost way more than a mains to 5VAC transformer.

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Jack A Lopez

4 years ago

This is possible, but a bad idea in most cases, because the resistors in your divider must dissipate significantly more power than goes to 5 volt load. The ratio of power wasted to power delivered is large, greater than the ratio of voltage in to voltage out. You can prove this to yourself using Kirchhoff's Laws.

The proof is left as an exercise for the interested reader.

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iceng

4 years ago

It will Kill someone

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