Basic AC-DC Converter Fundamentals

If we want to improve this converter, we should think of a way to draw power when the input voltage is both positive and negative.

Let’s take a look at how this operates. Here we are going to look at a four-diode rectifier. This is going from an ac input to a dc output. Now, we are going to use four diodes to help rectify this AC signal into a DC signal.

So, here is our setup as shown here. We have our four diodes and our load is a resistor, and it has this polarity. And we’re going to break it down into two stages.

First, we’re going to look at when we have positive voltage on the input. We have our AC wave, we have the positive voltage, that means the polarity in our input is going to look like the picture at 3:03. And we want the current the current to flow from the input to the output through these diodes.

We have so many diodes, where does the current flow? We want the current to flow through the resistor, because we want positive voltage on the output.

We have to go through diode number 2 in order to flow in that direction. Through diode 2, through this resistor, and then back towards the input to complete the circuit.

In order to get from this point to the input, we have to go through diode 3 here in order to complete our circuit.

So, you can see the current path. What this means is that if current is flowing, our polarity has to be forward biased.

So, here we need positive, negative voltage which we see from our input we would be getting that voltage over our resistor and then all the way through to our diode number 3.