DC Power Supply

Rebuild my DC Power Supply is something I was planning a long time but just now, had the chance to make it happen.

(click on the pictures to enlarge)

Why rebuild the power supply?

- Make a new PCB with circuit supporting higher currents.

- Add an ammeter.

- Develop a voltmeter based on arduino (previous one was using the pair CA3161 / CA3162).

- Develop a better assembly by taking advantage of CAD design and 3D printed parts.

- Make independent modules to make assembly and maintenance easier.

- Make a new panel layout.

Started by developing a PCB to hold the set of 7 segments displays and later the development of voltmeter/ammeter based on arduino.

Voltmeter based on Arduino was a piece of cake but had a hard time with ammeter. Shunt with very small resistance did not provide good resolution and by using higher values, voltage to load was becoming seriously compromised. Tried amplify the signal with op amps also but results did not convince . Also used ACS712 but did not get good resolution as well. I gave up and bought a commercial voltmeter/ammeter.

While waiting for the package, continued the development of other parts of the power supply...

Project decision was use 2 transformers. A small one to supply power to voltmeter/ammeter and generate a fixed 5v output for digital circuits development. A second one (main) to provide power for the 0 to 12v adjustable output with 3A max. A base where I could fix the 2 transformers was developed to hold both transformers in a single piece.

I no longer had the power supply circuit so I did reverse engineering on the old PCB to recover it.

The main PCB have 3 power supplies:

- A 7805 based to supply power to the voltmeter/ammeter.

- A 7805 based to supply power to 5V output.

- A LM324 based regulator and high power transistors for the adjustable 0 to 12v output.

The last stage of the main power supply uses a 2N3055. Developed a support to hold it. I don't expect the heat synk be hot enought to melt the 3D printed support (PLA melts at 190 celsius).

The 2N3055 is attached to the main board so everything remains in a single piece.

When received the package realized that digits from the voltmeter/ammeter were not what I expected. I disassembled the voltmeter/ammeter and removed the displays. See the digits I wanted versus voltmeter/ammeter digits.

So a new PCB with the regular .56 inch 7 segments displays was developed.and 3D printed a support to attach the voltmeter/ammeter board to the displays board.