A power supply is a device used to convert electrical energy from one form to another. This is done because the characteristics of the power being supplied are usually different from the characteristics of power needed by a certain device. For example, the source of power could be mains electricity with an alternating current of between 50 and 60 Hz and a voltage of 240V. This power could be used to power a desktop computer, with components that use a maximum of 12V direct current. A power supply will be needed to step-down the voltage from 240V to 12V.
In the above example, the power supply is changing the voltage as well as the nature of the current. However, in different scenarios, different conversions are needed. There are power converters that change DC to AC power. In addition, electrical devices have different power input requirements. A device may require a unique frequency, voltage, or current.
As such, there are many types of power converters to cater for the different demands of electrical devices.
These include dc-dc converters, ac-dc converters, ac-ac converters, and dc-ac converters.
Dc-Dc Converters
The dc to dc converter is used to change direct current from one voltage to another. Initially, this was done by using a vibrator to convert the dc input to alternating current. This was then stepped up to the required voltage using a transformer. The output was then rectified and supplied to the electrical load. The designs used to implement this were expensive and inefficient.
Over time, this process has undergone improvements that make it more efficient. The use of integrated circuits and semiconductors has fuelled these improvements.
A dc to dc converter is typically used in devices that are primarily powered by batteries, such as laptops and smartphones.
It is also used to maximize energy harvest in wind turbines and photovoltaic systems.
Dc-Ac Converters
A dc to ac converter, also called an inverter, is used to convert direct current into alternating current. This application is common when using battery power. Typically, power is taken from the dc power source, passed through the inverter, then supplied to the electrical device.
Power converters can perform their function through an entirely-electronic setup or through a setup that incorporates mechanical processes.
The output of an inverter is usually regulated to the same frequency and voltage as that of the mains ac supply. An exception is in vehicles, where variable frequencies are used to control speed. The inverter can have different output waveforms, including a square wave, sine wave, or pulse width modulated wave.
Examples of areas where a dc to ac converter is used include in home energy systems, in automotive electrical systems, in photovoltaic solar panels, and with the battery packs in electric vehicles.
Ac-Ac Converters
These convert AC current from one waveform to another, usually with different output voltages and frequencies. AC-AC converters can be classified into AC voltage controllers, DC link converters, cycloconverters, matrix converters, and hybrid matrix converters.
These classes of ac-ac converters can be further broken down. For example, cycloconverters can be classified according to the mode of operation, number of phases of output voltage, and the firing angle of positive and negative limbs.
Such converters are often used in speed controlling of machines, and for low-frequency and variable voltage magnitude applications.
Ac-Dc Converters
These are common and have a wide range of applications. They convert alternating current to direct current and are also called rectifiers. These converters are necessary because while electricity is supplied to households in alternating current, most home appliances use direct current.
The process of converting from ac to dc is called rectification because it corrects the current from a sine wave into a straight line. Rectification can be half-wave or full-wave. In some cases, additional smoothing of the output is required. This is done by electronic filters. The output may also be passed through a voltage regulator to ensure that constant voltage is supplied.
