Understanding AC/DC Power Supplies

What is the AC/DC Power Supply?

A power supply regulates input electricity and turns the energy to output power with the required range of voltages and frequencies for its application. The AC/DC power supply converts an alternating current power input into a direct current output. It is a necessary component of the modern automation system such as PLC, sensor, network devices to name a few. AC/DC power supplies provide electricity with consistent, stable, and clean voltages to this electronic system in need.

In this article, we will walk you through the overall ideas on what AC and DC are and how the AC/DC power supply works. We will also talk about different types of power supplies as well as their applications. Before diving deeper into the working principle and functions of AC/DC power supplies, let us spend some time and take a closer look at what alternating current and direct current are.

Alternating Current

Alternating current, or simply AC, refers to the electric energy that comes out of the power plant, electromechanical generators, or any power-generating facilities. The AC power has the voltages alternate in polarity, the magnitude changes, and the current reverses its direction constantly. An AC current moves in the form of waves and transports a great amount of energy with minimum energy loss. It has the ability to travel across a notably remote distance and this is exactly why the electrical grid delivers the alternating current from the power source to the outlet sockets in the household and business settings.

The primary application of alternating current lies in the power-generating industry, transportation industry, large commercial settings, and power electric motors. Although most electronic apparatus does not run on AC power, there are a number of home appliances we are familiar with directly consuming AC power, such as refrigerators, toasters, dishwashers, and conventional hair dryers. These appliances connect to the wall socket directly with a plug and use the AC power because AC/DC power supply or adaptor already is embedded inside.

Direct Current

The DC power, as opposed to the AC power, is unidirectional energy that does not reverse its direction as it flows in a circuit. The power source of a DC power is typically the battery, fuel cells, alternators, or solar cells. A DC current does not change the polarity of the voltage. The power level, voltage, and frequency are consistent, clean, and stable, which allows better efficiency and performance for electronic devices. AD/DC power supplies (or adaptors) are required when running most electronics.

How is the Utility Power Delivered?

Compared with the AC power, the DC power delivers a much lower level of voltage and runs a short distance. The delivery of the utility power can be depicted as simple as such: the power plant generates the AC power and delivers the power through the electrical grid to the sockets or outlets in an area. The end-user can use it directly (AC) or convert it into DC power for the end application. The delivery of utility power involves changing the voltage of the power and it is extremely inefficient and dangerous to use DC power, which is why the electrical grid delivers AC power instead.

How does the AC/DC Power Supply Work?

AC/DC power supply converts 110/240 VAC into target DC voltage. Currently, AC/DC power supply has linear and switch-mode on the market.  In brief, the linear mode power supply mainly uses a transformer to scale down voltage. The ratio of primary side to secondary side equals the same ratio of voltage transfer. For example, the ratio of 10:1 reduces the 120 VAC into 12 VAC on the secondary side. On the other hand, switch mode power supply switches mains electricity rapidly by FET to reach target voltage depending on on-time and off-time. By applying switching techniques, the bulky transformer can be reduced in size providing a compact design of power supply. Although the transformer used in a switch mode supply is much smaller and cheaper than that used in linear supply, the transformer in switch mode must be capable of handling the higher switching frequencies.  

Linear Power Supply

The linear AC/DC power supply is a more simple type. It works by a relatively straightforward mechanism. In this type of power supply, the three fundamental components are the transformer, the rectifier, and the filter. When an AC input first enters the power supply unit, the transformer scales down its voltage to the required level for the end application. Next, the rectifier converts the AC current into the DC current. The filter reduced noise and improves the quality of the current. Owing to the simplicity of design, the linear method is less efficient than the switching method. It also comes with a couple of drawbacks.

One of the disadvantages is the size of the unit. Since the linear type reduces the voltage at the input (the input voltage is usually around 150kV to 800kV and the output 120V or 240V), the transformer has to be relatively large to process the energy. The other disadvantage is the unit dissipates the excess energy in the form of heat. The regulating process generates a huge amount of heat, which requires large heat sinks to deal with. The power supply has to get rid of the heat to provide a constant output voltage. The size of the transformer and heat sinks make it impossible to downsize the linear power supply and therefore lead to a heavy, space-consuming unit. The linear type works best for high-power transforming applications.

Switching Power Supply

The switching type AC/DC power supply, also switched-mode power supply, successfully solves the size and heat problems that come along with linear power supply. The switching power supply works best when dealing with high-frequency power input. Switching mode power supply is realized thanks to the advent of semiconductor technology. The more efficient yet complicated mechanism allows for compact size without enormous heat generated. A switched-mode power supply (SMPS) is an electronic circuit that converts power using switching devices that are turned on and off at high frequencies, and storage components such as inductors or capacitors to supply power when the switching device is in its non-conduction state.

Types of AC/DC Power Supplies

Based upon the end application, the AC/DC power supply can be grouped into several types. In this section, we will take a look at the most common types and scenarios to use them.

Open/enclosed Frame Power Supply

The open-frame and enclosed power supplies are frequently used on infrastructure applications such as traffic lights and pedestrian signals. The main difference between these two types is the frame configuration. The open-frame power supply has all the electrical components attached to the PCB board without an external case to protect the interiors. The key advantage of this type is the excellent air convection. It is recommended to use the open-frame unit in a dust-free and contaminant-free environment. The enclosed power supply, on the opposite, has a case that covers the interior's electric circuit. Although the case is perforated to allow for a certain degree of convection, heat accumulation sometimes causes a problem. The advantage is that the casing structure provides physical protection to humans and the power supply itself.

AC/DC Power Supply Adapter

This type of AC/DC power supply usually comes with portable equipment and mobile devices. If you have no idea what the adaptor is, one example that you must be familiar with is Apple’s USB-C power adapter. With this type of power supply, we can charge the device by connecting the USB-C wire cable to the wall socket. The main application of the AC adapter is the various types of electronics, including laptops, pads, screens, monitors, TVs, printers, and smartphones. It comes with an additional accessory to the wire cable.

Industrial Power Supply

Industrial AC/DC power supplies refer to the electrical units that are designed exclusively for the industrial field. These power supplies are built with robust construction and multiple protections, such as overload protection, overheat protection, over-voltage protection, etc. This type of unit is ideal for machine and networking systems, which usually have to handle high loads and high density of energy. In addition, industrial AC/DC power supplies often have to work in extremely harsh environments with high temperatures, dust, and moisture involved. Acro Engineering develops a wide range of AC/DC power supplies for all types of industrial applications. Leave us a message if you need our services and professional consultation.