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I was doing research on AC to DC power supplies and I came across a lot of schematics that use regulators like the one below:

Linear Voltage Regulator credit: http://www.instructables.com/id/Make-a-simple-12-volt-power-supply/

Initially I drew out what I thought an AC to DC schematic would be and I basically did everything except including the LM7812 regulator.

Is it necessary or could someone get an equally good power supply by just using an effective transformer, bridge rectifier, and capacitors?

From the (Wiki) page it says the regulator is, "... conceptually an op amp with a relatively high output current capacity." Why this might be important, I do not know.

It seems to be the de facto standard in the AC to DC converter world and I would really like to know the importance of it.

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  • \$\begingroup\$ you could use a switching regulator instead of a linear regulator. \$\endgroup\$ – Jasen Dec 2 '15 at 4:26
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The rectifier alone produces very rough DC; it is not smooth at all and contains much of the AC signal called "ripple."

AC to Unfiltered DC (Courtesy of Wikipedia)

A filtering capacitor helps to smooth this out some, but the output is still not perfectly invariant.

Rectified and Filtered DC (Courtesy of Wikipedia)

The addition of the 7812 in this schematic, regulates that DC down to 12v, and eliminates almost all of the remaining ripple, producing a very nice and clean DC output.

There is nothing stating that you must use a regulator; and in fact, they are sometimes not used. Such as if the power supply were just lighting a lamp or operating a fan. Those "loads" do not require precise power control. But for more sensitive electronics such as digital IC's and analog chips, their supply voltage must remain very steady for correct operation. So the answer is, whether or not to use a regulator depends on the application. :)

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    \$\begingroup\$ The "very rough DC" is often called "pulsed DC". \$\endgroup\$ – Fizz Dec 3 '15 at 22:20
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Some applications will tolerate unregulated noisy supplies. Motors, for example. So no, you don't always need a regulator.

And if you do, it doesn't have to be a linear regulator : a switching regulator is more efficient and runs cooler, but it can be harder to keep the switching noise under control. So a switching regulator is fine for digital logic or a computer, but a linear might be easier to use (but not the only option) for sensitive audio or radio circuits.

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Regulators are required to provide a known, stable, ripple-free output voltage.

Without the regulator, the output voltage of the supply would vary with load, and the output would also have some "ripple voltage" which would also vary with the load on the supply. The output voltage of a simple rectifier/capacitor power supply would also vary with the AC input voltage.

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  • \$\begingroup\$ There are however quite a few applications which can tolerate such ripple and variation. \$\endgroup\$ – Chris Stratton Dec 2 '15 at 1:37
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Switched mode power supplies are now the de-facto standard.

linear power-supplies with an iron transformer driven directly from the mains are now a specialty item.

The regulator is needed if the fluctuations due to the pulsed current from the rectifier and variations in the line voltage give unsatisfactory results.

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  • \$\begingroup\$ I didn't know about switched mode power supplies, thanks for that. \$\endgroup\$ – Klik Dec 3 '15 at 19:28
  • \$\begingroup\$ The down-side to switched-mode power supplies (SMPS) is that they can be rather complex to very complex, challenging to build properly, and sensitive to parasitic aspects of the design (such as the length and shape of of wires and traces.) While they may be most common today for their efficiency and size, most designs are not really suited to beginner-level electronics. \$\endgroup\$ – rdtsc Dec 4 '15 at 12:47

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