AC/DC Converter with Voltage Regulator

This was one of the first projects I worked on. I made it for my final assignment in Basic Electronics class. Just to clarify, the picture above is not my actual university project. I left that version in a drawer long time ago and cannot access it right now. So, I remake it in Fusion 360 as a 3D model and put the picture there.

This is a 3D viewer of the model. Use left mouse button for free orbit and right mouse button to pan. Use landscape mode if you are on a phone for a better view.

I assembled the parts and drew the wiring in Fusion 360 so it can be embedded online. However, besides the fasteners, I made all the other 3D parts by myself in SolidWorks. They are uploaded here for everyone to use.

schematic

This is the schematic of the circuit. It uses a transformer to step the voltage down from 220V to 18V.

Four diodes are connected as a typical full-wave bridge rectifier to convert the AC voltage into a positive DC output.

A capacitor is included to smoothen the voltage, and lastly, an LM317 IC is used to regulates the output voltage.

I didn't use circuit protection like a flyback diode or fuse, because this was my project for Basic Electronics class assignment, and I didn't know much about components yet.

PAD 1 & 2 → Transformer

PAD 3 & 4 → 7-Segment Voltmeter

PAD 5 & 6 → Output Wire

circuit Simulation

The output voltage of LM317 IC can be adjusted by modifying the resistance ratio between the output and adjust pins. It can be calculated using the following formula:

R1: the resistance between output and adjust pin.

R2: the resistance between adjust pin and ground.

Voutput = 1.25 × (1 + R2 / R1)

By using a 240 Ω resistor and a 2200 Ω potentiometer, theoretically, we can get an output range between 1.25 V and 12.7 V by turning the potentiometer. Since the LM317 IC requires an input voltage at least 3 V higher than the output, a minimum of 15.7 V is needed at the input pin.

Below is the simulation of how the circuit works (you may refresh if it doesn't load). See how the voltage changes in each section, and use the slider to simulate how turning the potentiometer affects the output. For a better view, please switch to landscape mode if you are on a phone.

PCB

After creating the schematic, I designed the PCB in Autodesk Eagle. I placed the routing on the bottom layer since I was using through-hole components.

I then linked the Eagle software to Fusion 360 to automatically generate a 3D model of the PCB, and here are the results.

Improvement Ideas

I think the safety level could be improved by adding a fuse at the output to prevent short circuit risk, and a flyback diode to protect the circuit from back EMF in case it's used to power a DC motor. Adding a switch to turn the device on and off completely is also a good idea since it cannot reach a 0 V output when plugged in.

Overall, I definitely recommend electrical engineering students to make AC/DC converter with voltage regulator for assignment during early university studies. It was very helpful when building future projects. I often used this device when working on other assignment projects. I did not have to waste batteries, and it eliminated the hassle of continuously plugging and unplugging them.

AC/DC Converter with Voltage Regulator

schematic

circuit Simulation

PCB

Improvement Ideas

See Also

My Personal 3D Models

Remote-controlled Bipedal Toy Robot