Semiconductors What are diodes and rectifiers?
Two components that are essential to the operation of a vast range of electrical devices are diodes and rectifiers. Without them, the electrical current could flow back into other components, causing damage or total system failure.
This article looks at the difference between diodes and rectifiers, their respective workings and applications.
Diodes: the protector of modern electronics
As the simplest semiconductor device, diodes are usually two-pin components made from silicon or germanium. Their purpose is to allow current to flow in one direction while preventing it from flowing in the other. When installed in a larger system, the diode protects sensitive electronic parts from being subjected to the wrong amount or type of current.
A basic example: a TV remote has a compartment for two AA batteries. When the batteries are inserted correctly, the diode allows the current from the batteries to flow through the circuit in the remote, enabling the remote to be used correctly. When the batteries are inserted the wrong way around, however, the diode automatically blocks the current from leaving the batteries in the reverse direction. The remote will not work, but the sensitive electronics are safeguarded.
There are many types of semiconductor diode, including:
- Avalanche diodes, to protect circuits from high voltage surges
- Zener diodes, to regulate voltage
- Varactor diodes, to electronically tune TV & radio receivers
- Light-emitting diodes (LED), to produce light
- Tunnel diodes, to generate radio-frequency oscillations
Rectifiers: a diode with superior current handling
A rectifier is a special type of diode that converts alternating current (AC) into direct current (DC). This is an important process, as alternating current is able to reverse direction periodically, while direct current consistently flows in a single direction, making it simple to control. There are multiple types of rectifier, including:
Half-wave rectifiers: rectifiers that permit only half of the AC signal to pass from input to output.
Full-wave rectifiers: rectifiers that use the full signal, requiring the additional use of a transformer.
Positive half-cycle rectification: those where a top diode with positive polarity conducts current while a bottom one with negative polarity blocks it
Negative half-cycle rectification: those where the top diode is blocked and the bottom one is opened.
Domestic appliances generally contain a diode designed for single-phase rectification, meaning the supply voltage changes in unison. Industrial-scale motors and power grids, on the other hand, require multi-phase rectification, which allows for power generation, transmission and distribution at the same time.
Applications for diodes today
As an integral part of a silicon chip, diodes are found in a huge range of electronic devices. In a microwave oven, for example, a diode works alongside a capacitor to double the voltage conveyed to the cavity magnetron (which generates the microwaves). Diodes are also used in keyboards as part of matrix circuits, which reduce the amount of wiring required. Researchers have even developed nano-scale diodes from a single DNA molecule, which may lead to even smaller, more powerful electronic devices in the near future.
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