Rectifiers

At the basic level, rectifiers are nonlinear circuit components that allow more current to flow in one direction than in the other. The perfect rectifier would let current flow freely in one direction and not allow it to flow at all in the other direction.

Some people like to think of rectification as being a switch action. In the ON position the switch allows for current to flow and in the OFF position no current at all can flow back. Rectifiers are used primarily for the conversion of alternating current (ac) to direct current (dc).

There are different types of rectifiers, and there are a variety of rectifier elements in use. Here are a few of the more common ones.

The vacuum-tube rectifier can efficiently provide moderate power. Its resistance to current flow in the reverse direction is essentially infinite because the tube does not conduct when its plate is negative with respect to its cathode. In the forward direction, its resistance is small and almost constant.

Gas tubes, used primarily for higher power requirements, also have a high resistance in the reverse direction which allows them to act as rectifiers as well.

The modern semiconductor rectifier has the advantage of not requiring a filament or a heater supply (which are found in tubes). This type of rectifier has constant forward and reverse resistances, with the forward resistance being much smaller.

Mechanical rectifiers can also be used in some applications. The most common is the vibrator, but other devices are also used.

In general, all rectifiers can be classified as controlled and uncontrolled rectifiers. The controlled rectifiers can be sub-divided into semi-controlled and fully-controlled rectifiers.

Uncontrolled rectifier circuits are built with diodes, and fully-controlled rectifier circuits are built with SCRs. Both diodes and SCRs are used in semi-controlled rectifier circuits.

There are many rectifier configurations. The more common rectifiers and their configurations include: Single-phase semi-controlled bridge rectifier; single-phase fully-controlled bridge rectifier, the three-phase three-pulse, star-connected rectifier; double three-phase, three-pulse star-connected rectifiers with inter-phase transformer (IPT), and the three-phase semi-controlled bridge rectifiers.

These are just a few of the configurations possible. Anyone interested in industrial electronics or electronics in general should spend some time studying the principles behind rectifiers. These devices are being used more often today than ever before and most electronic enthusiasts will come into contact with them sooner or later. You will need a good working knowledge of schematics when you begin working with rectifiers.