What is a Power Rectifier?

A power rectifier is a device used to turn alternating current (AC) power into direct current (DC) power. A rectifier is the opposite of a power inverter, which turns DC power into AC power. Many small household appliances such as laptops, televisions, and video game systems use these devices to create usable power.

There are two basic kinds of electric power. AC power periodically reverses direction from negative to positive and back. DC current does not reverse direction.

Since AC power can be transferred through wires with minimal losses, the power that goes from the electric company into the average home is AC power. The problem is that most small household devices run off of DC power. A power rectifier must be used to allow these devices to run when plugged into a common wall outlet.

It can be as simple as a single diode. A diode is a small glass and wire component that conducts electricity in only one direction. The single diode can act as a rectifier by blocking either the negative or the positive AC current.

A power rectifier that uses a single diode performs half-wave rectification. This means that only half the wave reaches the output. It is inexpensive and easy, but very inefficient.

Efficiency can be increased by using several diodes. A full-wave power rectifier converts the whole AC signal into DC power. This method requires four diodes in a formation called a diode bridge.

A full wave rectifier similar to the diode bridge can be made using a transformer and two diodes. The transformer must have a center tapped secondary winding. This means that a connection is made half way along the transformer. This is more efficient than the single diode but more expensive than the diode bridge method. Other forms of rectifiers exist, but these are the most commonly used.

The main problem with any rectifier is that AC power has peaks and troughs. DC made from this kind of power does not have a constant voltage. This can cause complications with electrical equipment.

To produce a steady DC signal, the power rectifier must be coupled with some sort of smoothing circuit or filter. The simplest of these is a reservoir capacitor placed at the power rectifier output. The larger the capacitor, the more the ripple will be smoothed. The drawback is that a large capacitor will create higher peak currents.