Simple full wave rectification using a homemade PCB

In order to better understand rectification of alternating current, I designed a PCB for full wave rectification and manifactured it using my CNC-Router. This circuit was not designed for high voltages or currents, but can rectify a sine wave to a near perfect DC, at least according to my oscilloscope.

What is full wave rectification?

Full wave rectification is a method of converting alternating current (AC) into direct current (DC) using diodes and capacitors. There are a lot of tutorials on this online, so I am just going to give a quick overview on how it works:

Schematic, found here

The four diodes in the shown configuration only allow the current to flow in one direction. Try to imagine which path the current takes through the diodes, depending on the polarity of the source. You’ll find, that the current will always flow from the node D1D3, through the load, to D2D4, no matter the polarity. Effectively, this flips the negative parts of the sine wave into being positive, so that the current only flows in one direction.

Ideal graphs of normal AC (blue) and rectified AC (green).

Now, at this point, technically, this is direct current, since the direction of the current never changes. But since we usually want a smooth DC without any ripples, we need a way of get rid of the half-sine shape. A way to do this is to store the energy (rather: voltage) of the sine wave at the maximum (see the spots in the graphs) until the next maximum is reached. Short term energy storage in electronics is usually done by capacitors, so this is what is used here. Effectively, the capacitor is charged whilst the sine wave is above a certain threshold, and discharged below. This keeps the voltage at a constant level, as long as the capacitor can store enough energy to “bridge” the low voltage part of the wave when the load is connected. During this part, the capacitor is the effective power source of the circuit.

This is how this circuit looks on my oscilloscope (simple 6V AC from a transformer):

Without capacitor..

With capacitor!

Making the PCB

I designed this simple circuit in Fusion 360 Electronics and milled it on my homemade CNC-router. This was the first PCB I made, so its not perfect, but is does the job!

For the components, I just used whatever I found in my box, since this circuit is just for demonstration/learning purposes. The diodes are simple 1N4007 diodes and the capacitor is rated for 35V 680µF, so this PCB can rectify up to 35 Volts.

So, this is how this specific PCB looks on the oscilloscope:

Blue line: Half wave rectification of one diode. Yellow line: Rectified output voltage.

As you can see, the DC output is pretty much flawless, because the capacitor is never discharged. Of course, if we were to connect a load to the circuit, this would change and the output waveform would be become less perfect (more ripples, lower mean voltage).

I hope you found this short excursion into the world of electronics interesting!

As always: Thanks for reading!