A triple voltage supply from a dual supply

Question

I have build a dual power supply for an analog synth (see image below).

The input source is a 12 VAC - 1.7A adapter. It is based on the Wall Wart power supply from Music from Outer Space.

Now I would like to include a 5V output to drive one or more Arduinos. If I expand the power supply with a voltage regulator (LM7805) in parallel with the LM7812 regulator, would this work?

I expect that the LM7805 regulator will be less efficient as it has to bring the voltage down from 12V to 5V and will produce more heat. Therefore, I've attached all voltage regulators to heat sinks.

Might it be better to exchange the LM7805 linear voltage regulator with a switched voltage regulator? The advantage being that it is more efficient and produces less heat, while the noise might increase. I do not intend to use batteries, so efficiency is less important, and I expect that the Arduino will not take much current.

An additional question: Have I placed the fuses F1 and F2 at the correct position in the circuit?

Answer 1

Figure 1. OP's original circuit, since removed.

You haven't copied the power supply from Music from Outer Space correctly.

^{simulate this circuit – Schematic created using CircuitLab}

Figure 2. You can't always get what you want. This time you're lucky.

Your arrangement in 1(b) has no ground reference between the supply and your capacitors. The voltages will be all over the place.

1(a) will work.

One fuse will suffice. Add it on the upper winding output. That way it provides protection should anything happen on the diodes or smoothing capacitors.

Figure 3. The RS 78xx series switching regulator.

There are a variety of three-pin 7805 replacements which have a built-in switching regulator in a package a little bigger than the 7805 1 A version. Use those for efficiency. e.g. RS K78xx series.

Answer 2

a) To protect against capacitor failure, delete F1 and F2, and use a single fuse ahead of D1/D2.

b) Since efficiency and size are not factors, I vote for the linear 5 V regulator. Note that most small buck regulators require external input and output capacitors. Also, "proper" grounding techniques are very important for conducted noise control, but they vary widely depending on the physical arrangement of the components. KISS.