Is a Rectifier a Non-Linear Device and What is the Process of Rectification?

Some say that the history of power electronics began in 1902 with the invention of the pool-cathode glass-bulb mercury-arc rectifier. The credit for this revolutionary non-linear device goes to an American inventor named Peter Cooper Hewitt. He made his discovery while experimenting with a mercury vapor lamp that he patented in 1901. Through his experimentation, he discovers that current flows in only one direction, from anode to cathode, therefore providing rectifying action.

The invention of the mercury-arc rectifier paved the way for many electronic devices that are an indispensable part of our daily personal and professional lives. There is no wonder why some consider its invention the beginning of the classical era of power electronics.

What is a Rectifier?

By definition, a rectifier is an electrical device that converts AC (alternating current) that intermittently reverses direction to DC (direct current), which only flows in one direction. A rectifier is a component of a circuit that allows current to pass in one direction while preventing its flow in the other direction. In terms of applications, you can find a rectifier in use in a typical desktop power supply unit.

The rectification process itself involves a device that only allows electrons to flow one-way. As You may know, that perfectly describes the functionality of a semiconductor. Moreover, the most basic kind of rectifier circuit is a half-wave rectifier.

However, physically, a rectifier can be in a variety of forms, including mercury-arc valves, semiconductor diodes, vacuum tube diodes, and even wet chemical cells, to name a few.

Above is a simple half-wave rectifier. Typical uses for rectifiers are going to be in desktop power units. 

Rectifier Applications

In terms of applications, rectifiers have a myriad of uses. However, they typically serve as components in DC power supplies or high-voltage DC power transmission systems. The process of rectification also has multiple applications as well. For example, it can serve in the role of detectors of radio signals, or flame presence detectors in Gas-heating systems.

Moreover, depending on the type of the AC supply and the rectifier circuit’s arrangement, a rectifier’s output may require further smoothing to produce an output (voltage) that is both uniform and steady. Most rectifier applications need a stable and constant DC voltage, i.e., power supplies for PCs, TVs, and radios. Therefore, to accommodate these requirements, rectifier designs incorporate electronic filters to smooth out a rectifier’s output.

In general, these electronic filters can be capacitors, a set of capacitors, a choke, or chokes and resistors, which are typically followed by a voltage regulator to produce a steady voltage.

Rectifier Devices and Types of Rectifier Circuits

Prior to the use of silicon semiconductor rectifiers, there were copper oxide-based and selenium-based metal rectifier stacks, as well as vacuum tube thermionic diodes. However, with the onset of semiconductor electronics, the obsoletion of vacuum tube rectifiers was inevitable. Fast-forward to the present day and various types of semiconductor diodes are in use for rectification ranging from the extremely low to the extremely high current applications.

When simple rectification is not enough, in the case of variable output voltages, other devices are put into service. These other devices, of course, are also capable of controlling electrodes and providing the unidirectional flow of current as well. Moreover, these types of high-power rectifiers are in use in high-voltage DC power transmission, and they incorporate various types of silicon semiconductor devices.

In general, these types of rectifiers are called thyristors. These and other controlled switching solid-state switches, effectively function as diodes to pass current in only one direction.

Overall, a rectifier circuit can be multi-phase or single-phase, but the majority of low power rectifiers in use in domestic equipment are single-phase. Also, three-phase rectification is essential in industrial applications and for high-voltage DC transmission.

Single-Phase Rectifiers and Half-Wave Rectification

In the case of a single-phase supply with half-wave rectification, only half of the AC wave will pass, while it blocks the other half, regardless of polarity. Since only half of the input waveform reaches the output, this translates into a lower output voltage. Also, half-wave rectification entails the use of a single diode in a single-phase supply and three diodes in a three-phase supply.

In general, a rectifier produces DC outputs that are both unidirectional and pulsating. A half-wave rectifier generates far more ripple compared to a full-wave rectifier. This, of course, means that it requires significantly more filtering to eliminate the harmonics of the AC frequency from its output.

Single-Phase Rectifiers and Full-Wave Rectification

A full-wave rectifier converts the entire input waveform into a single and constant polarity output (positive or negative). Full-wave rectification converts both polarities of the input waveform into pulsating DC, which results in a higher output voltage.

In terms of design, you can create a full-wave rectifier with either four diodes in a bridge configuration or two diodes and a center-tapped transformer and an AC source, which can be a transformer without a center tap. For example, a single-phase AC supply, with a center-tapped transformer and two diodes back-to-back (anode to anode or cathode to cathode), can form a full-wave rectifier. Although it requires twice the turns on the transformer’s secondary to produce an equal output voltage than say a bridge rectifier, its power rating remains unaffected.

Multi-Phase Rectifiers

A single-phase rectifier is commonly in use in power supplies for domestic equipment. In contrast, high-power and industrial applications generally use multi-phase rectifiers. Like with single-phase rectifiers, three-phase rectifiers may also take the form of a half-wave circuit, a full-wave bridge circuit, or a full-wave circuit using a center-tapped transformer.

You can commonly find a thyristor in use to replace a diode for voltage output regulation. Moreover, the majority of devices that provide DC also generate three-phase AC. Such as the case of automobile alternators that contain six diodes, that function as a full-wave rectifier to charge your car battery.

Note: A thyristor is a solid-state semiconductor device with four layers of alternating P- and N-type materials. Moreover, it functions solely as a bistable switch that conducts when the gate receives a current trigger and stops conducting with the removal of voltage. Furthermore, the method of removal is typically through reverse biasing, but it can also be through other means.

Without proper understanding of power supply designs, you might find yourself lost in the world of rectifiers. 

There are many devices today that owe their functionality to the non-linear device we call a rectifier. Whether in a single-phase configuration or a multi-phase configuration, devices like TVs, radios, and even PCs could not exist. Although its invention dates back to the early twentieth century, our present would look very different without the rectifier.

Team design of nonlinear devices is made possible and efficient in the suite of design and analysis tools from Cadence. Starting with layout, Allegro PCB Designer is sure to have any tools and specialties necessary for the design and implementation of power supplies and other necessary circuit considerations. 

 If you’re looking to learn more about how Cadence has the solution for you, talk to our team of experts and us.