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Limitations of the Single-Diode Rectifier. A single-diode rectifier is a very simple type of AC-DC converter. It is only able to supply power from the AC source to the DC load when the input voltage is positive.

But, when the input voltage is negative, no power is transferred from the source to the load. Even though the input is able to provide power during this stage. In other words, only half of the AC waveform is rectified to DC, and the other half is essentially ignored.

Also, if we want to maintain a relatively constant output voltage, we need a relatively large output capacitor.

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.

As we saw from the single-diode rectifier, AC-DC converter, power is only drawn from the input when the input voltage is positive.

To increase power utilization, we may want to draw power during both positive and negative stages.

To achieve this, we use a slightly more complicated circuit topology that utilizes four diodes. This four-diode rectifier is very commonly used when going from AC input to a DC load.

Let’s take a look at how this operates in the next pages.