Electronic – Location of diode bridge on transformer circuit

bridge-rectifierpowerpower supplyrectifiertransformer

I'm designing a full bridge rectifier that takes 110vAC to 4-16vDC for input into a 5v switching regulator.

I opened a few 5v power supplies and they place the bridge on the high voltage side. Why not use the low voltage size so the diodes are smaller/cheaper?

Also, I notice they use an IC on the high voltage side, what is the purpose of that IC and is it required?

Most circuits I see online are basic like this one which should give me full wave recification:

enter image description here

This is the transformer I'm using:
http://catalog.triadmagnetics.com/Asset/FS10-600-C2.pdf

Best Answer

You're confusing the "oldfashioned" linear mains supply like this:

enter image description here

Reasons to use this design are:

  • It is a simple design
  • As long as you don't touch the primary side of the transformer, it's pretty safe

With the more modern switched mode power supply:

enter image description here

As you can see the switched mode supply is much more complex !

Reasons to use this design are:

  • the transformer is used a a much higher frequency than the 50 or 60 Hz mains frequency meaning that it can be much smaller and more efficient
  • the smoothing capacitors after the transformer can be smaller
  • being a switched supply means that it is much more efficient
  • it can be made more compact (because of reason one)
  • it can be made cheaper (no expensive transformer)
  • lighter in weight, easier to carry.

For Bonus points:

Here's a "circuit level" example of a simple switched mode mains supply, note that it has 2 outputs, 5 V and 12 V. You could leave out the 12 V output to make it even more simple.

enter image description here

Now compare that to the first schematic !

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