Explanations of plug-in transformers, lists of manufacturers, and descriptions of uses for plug-in transformers
You will learn:
Plug-in transformers are class 2 power supplies that are intended for connections with 15 ampere, 120 or 240 volt alternating current (AC) branch circuits. The classification of class 2 power supplies comes from Underwriters Laboratory (UL) 1310 that delineates the safety standards for class 2 power supplies and battery chargers. The purpose of UL1310 is to ensure the safety of users. Plug-in transformers are AC adapters and power supplies or class 2 power units.
There are three specific limitations regarding plug-in transformers. They are unable to provide more than 100 VAS of continuous power, cannot supply current under short circuit conditions, and have a safety extra low voltage (SELV) compliant open circuit voltage of 90V DC or 42.4 V peak AC.
Small plug-in transformers plug into a wall socket and create low direct current voltages for electronic devices. Plug-in transformers protect low voltage electronics from higher voltages and eliminate the need for cooling devices, which allows plug-in transformers to be smaller, lighter, and more compact. They keep heat away from sensitive circuits and supply lower output.
Transformers are electromagnetic devices used to transform or change power. The structure of a transformer includes a core and two coils that are designated as primary and secondary. As AC current is applied to the primary coil or winding, a magnetic field is created. The core directs the magnetic field to the secondary winding where the electric current becomes an electromotive force (EMF).
A plug-in transformer converts AC voltage to another form of AC voltage. Normally, 120-volt AC current enters the transformer, which converts the current down to a lower voltage. The normal current in most homes and offices is 120 volts, which is received by the primary winding that has the core running through the middle of its windings. In the primary winding, a magnetic field is created in the core.
The secondary winding, that is wound around the core as well, is where the magnetic field in the core creates current. The voltage of the current in the secondary winding is determined by the ratio of the number of turns in the two windings. If the two windings, primary and secondary, have the same number of turns, the voltage will be the same. If the secondary windings are half the number of turns as the primary windings, the voltage in the secondary winding will be half that of the primary winding. If the voltage is to drop to 3 volts in the secondary winding, the number of windings in the primary has to be 40 times more.
The primary and secondary windings share a common core around which the windings are wound. The core is the center of a plug-in transformer. It provides structural support for the windings and a path for the magnetic flux. As current flows through the primary winding, it creates magnetic flux, which cuts through the secondary winding that picks up the voltage. The secondary winding is where power is stepped down in accordance with the number of windings.
The cores for plug-in transformers take differing forms with some having two separate windings while others have two windings wrapped together around the core. Plug-in transformers with separated windings have the windings placed side by side or one on top of the other. Single winding plug-in transformers have their windings wrapped around the core with the primary winding wound closest to the core while the secondary is wrapped around the primary.
There are certain standards that are followed in the development of the core for plug-in transformers. The key characteristics of all cores for transformers are magnetic permeability and low magnetic resistance, due to the necessity of creating a magnetic field to transfer current. The cores for plug-in transformers take several different shapes depending on the design of the transformer. Common materials used for cores are different forms of iron and steel.
The two types of wires used to produce plug-in transformers are aluminum and copper with copper being heavier than aluminum but a better type of wire for plug-in transformers. The reason for the use of copper wires in plug-in transformers is due to its higher conductivity level with a resistivity of 0.6 times that of aluminum. For an aluminum plug-in transformer to perform at the same level as a copper wire plug-in transformer, it would have to be far larger and bulkier.
The primary winding is connected to the input power source while the secondary winding is connected to the load. Power is received by the primary winding that creates a magnetic field, which induces an electromotive force in the secondary winding. Windings are classified based on their input and output connections and the voltage levels they can handle.
Wire resistance is important to the performance of plug-in transformers and is affected by the materials of the core and wire, the length of the wire, temperature, and thickness. Resistance is the property of a conductor that opposes the flow of current. It is the relationship between the applied voltage and the electric current passing through. It is calculated using the length of the wire, the cross-sectional area of the wire, and the resistivity of the material from which the wire is made.
As wire gets longer, its resistance increases. With cross sectional area, the reverse happens. As the area of wire increases, its resistance decreases. The greater amount of space allows electrons to move through without generating any heat. The level of the resistivity of a material determines its resistance and its ability to conduct current. Each of these factors determine the efficiency of a plug-in transformer.
Thicker wire has lower resistance and allows current to flow through without overheating. With thicker wire, there is less resistance and energy flows through easily and less energy is lost as heat. In plug-in transformers, thicker wire can handle higher current due to its lower resistance.
While the core of a plug-in transformer is important, the characteristics of the wire windings determines the performance of a plug-in transformer and how it changes the current. In most cases, the primary winding has low resistance while the secondary winding has high resistance due to its thinner wires. The resistance value of the primary winding affects the amount of current that can flow through while the resistance of the secondary winding determines the amount of power a transformer delivers to the load. High resistance leads to voltage drops and power losses, factors that affect the performance of a plug-in transformer.
All electronics produce heat as a byproduct of their operation. In transformers, the increase in the temperature of windings can shorten the lifespan of a transformer. The rise in temperature in a transformer is related to the heat that is produced and that which is removed. Highly efficient plug-in transformers have little heat waste, which leads to lower temperatures.
The factor that impacts temperature increase in a plug-in transformer is its insulation, which is the maximum operating temperature of a transformer based on the maximum ambient temperature. The rating of the insulation is related to the increase in temperature, hotspot allowance, ambient temperature, and the margin of safety, a factor that determines a plug-in transformer's overload capacity.
Plug-in transformers are one of the most widely used types of electronic devices. They make sure that electronic equipment receives the correct amount of voltage. The three categories of electronic devices are dual voltage, 110V-120V, or 220V-240V. Plug-in transformers are used with 110V-120V and 220V-240V but are not required for dual voltage devices.
Many electronics require lower voltage than what is commonly provided through electric outlets. Wall plug-in transformers, known as wall bumps, power cubes, wall adapters, and wall warts, come in the form of plastic boxes that can plug directly into a wall socket. They are available in a wide range of voltages, power levels, and polarities. The use of plug-in transformers gives product designers greater freedom when confronted with high voltage issues for various types of electronics. In essence, plug-in transformers serve as a form of protection from high voltages for low voltage equipment.
The initial factors that differentiate the types of plug-in transformers are their voltages, power levels, and reversed polarities, which can be additive or subtractive. The performance of a plug-in transformer depends on how the winding coils are connected and the direction of the windings. If the finish end is connected to the start end, the transformer is additive. If the coils are connected in reverse, the transformer is subtractive.
The reference to polarity is in regard to how the primary and secondary windings relate to each other. With additive polarity, the windings add to each other. With subtractive polarity, voltage is subtracted from each winding. An understanding of the polarity of a transformer is important for designers and engineers when they are working with electrical power systems.
Interchangeable plug plug-in transformers refers to changes in the AC power supply using a removable plug. The design of interchangeable plug plug-in transformers makes it possible to select a plug configuration that fits the socket head of the local main. The most common use of interchangeable plug plug-in transformers is for international travel when plug configurations vary from one country to another.
The use of interchangeable plug plug-in transformers allows for versatility to meet the requirements of international power supplies. They are available with 100V up to 240V input with 24W5 up to 24VDC output with exceptionally high efficiency.
While North America has 110V to 120V coming out of outlets, the rest of the world has 220V up to 240V, which are also used in North America for large appliances. In order to use American electronics that have a lower voltage rating in other parts of the world, the voltage has to be lowered using a plug-in voltage transformer. The use of plug-in transformers is to protect American electronic devices from the higher voltages, such as 240V.
There is a wide assortment of plug-in transformers that can be used for converting voltages. It is important to examine the label on an electronic device to determine the voltage that it requires. Plug-in transformers can be purchased to match the voltage a device requires. All electronic devices identify their wattage with the letter “W”, which determines the plug-in transformer that is required.
A dual voltage plug-in transformer has one or more windings with two voltages, which makes it possible for the plug-in transformer to provide two different voltage values. The factor that determines a dual voltage plug-in transformer is its number of windings that are able to circulate different currents and voltages. Plug-in transformers that can handle multiple voltages have it printed on their label, a factor that is common to many modern electronics.
A transformer that converts input voltage to one or more output voltages is referred to as a dual voltage transformer. With most plug-in transformers, dual plug-in transformers step down voltage to meet differing electrical requirements. They have multiple tap settings that allow users to select the voltage levels and isolate voltages for safety. Dual voltage plug-in transformers offer flexibility and efficiency when managing power supplies for electronics with different voltage inputs.
AC to DC plug-in transformers are a simple method for powering electronics from an AC main. With an AC to DC plug-in transformer, the transformer is connected to an AC rectification circuit. After the AC voltage is increased or decreased, the rectification circuit converts the AC voltage to DC voltage. The central part of an AC to DC plug-in transformer is the rectification circuit with full wave rectification being the best way to convert AC voltage.
The two versions of AC to DC plug-in transformers are wall mount and desk mount. Wall mount AC to DC plug-in transformers plug directly into a wall socket and are connected to the load by a cable. Desk mount AC to DC plug-in transformers may be a stretch of the plug-in definition in that they are placed between the load and the plug-in socket.
Of the various types of plug-in transformers, 24 VAC plug-in transformers are the most common. They are used to step down 120 VAC or 115 VAC to 24 VAC that is used for low voltage lights, door bells, and other electronic devices. The use of 24 VAC plug-in transformers is for convenience and safety. They are easy to install and eliminate any concern regarding electrical shock. There are many varieties of 24 VAC plug-in transformers that come with varying lengths of cable. Like all forms of plug in transformers, 24 VAC plug-in transformers supply the correct amount of voltage to avoid damage to electronic devices.
Isolation transformers separate primary and secondary windings to keep the two circuits physically and electrically separated. The primary purpose of isolation transformers is to eliminate voltage spikes in supply lines that can cause disruptions in service and damage equipment. They are a reliable and safe device that reduce power surges, noise disruptions, provide harmonic corrections, and improve power quality. The wide variety of isolation transformers include ultra, galvanic, drive, and dry isolation transformers, which are designed for specific purposes and applications.
The function of isolation transformers is the same as that of all other forms of plug-in transformers. They adjust input voltage to match the required output voltage of the load. What differentiates them from other plug-in transformers is their ability to keep electrical equipment separated from the power source.
The six plug-in transformers that are described above are a small sample of the many plug-in transformers that are available. They are very flexible tools that come in several varieties to meet the requirements of an assortment of applications. While the majority of plug-in transformers are easy to purchase, install, and use, there are certain features and uses for plug-in transformers that can be explained by the manufacturers.
One of the challenges of working with electricity is its production of electromagnetic fields that can interfere with the performance of other electronics. While electromagnetic fields are a danger in industrial and manufacturing operations, protection against them is especially critical in the medical profession where multiple electronic devices may be positioned in a recovery room or surgical bay. Plug-in power transformers are an essential tool for such situations that helps protect equipment and patients.
The types of medical equipment that depend on plug-in transformers include dental tools, testing labs, and heart monitors. The inclusion of plug-in transformers ensures that medical devices perform properly and provide accurate readouts. Every aspect of human health requires stable electrical supplies that are protected from surges, spikes, and instabilities by plug-in transformers.
Isolation transformers for medical use act as a buffer between the power supply and hospital and medical equipment. As with all forms of plug-in transformers, isolation transformers lower voltage to fit the requirements of medical equipment. Their key feature is their ability to eliminate electrical spikes and surges, which can seriously damage sensitive and delicate equipment.
Wire selection when designing a plug-in transformer is an exceptionally critical factor since each type of wire provides benefits and drawbacks regarding the performance of a plug-in transformer. The most commonly used type of wire is insulated round copper wire, which is the wire to which most people are accustomed. The two forms of wire that are used in the manufacture of plug-in transformers are round wire and flat wire.
Wire for plug-in transformers are made of copper or aluminum with copper being the most popular due to the disadvantages associated with aluminum. The argument of copper or aluminum has been going on for years with aluminum being lighter while copper is a better conductor but bulkier.
Round wire has a round conducting section that is covered with an insulation that can be made of polyglass, polyamide, or polyester. The insulation for round wire comes in a wide variety of types, which are used in accordance with the application for which the wire is used.
The traditional option for the manufacture of plug-in transformers is round wire, which is less expensive and is the most efficient. With higher frequencies, round wire can suffer the skin effect, where current flows along the surface of the wire, increases the wire’s resistance, a factor that can be overcome using Litz wire.
The cross-sectional appearance of flat wire is rectangular or square, a shape that has benefits that are unlike those offered by round wire. It is manufactured by pulling or drawing copper or aluminum through a die with the cross-sectional appearance of the required shape. The result of the process is thinner wire with the same width as round wire.
The shape of flat wire makes it more flexible, easier to shape, and allows for more contact points. Since space is limited in plug-in transformers, flat wire is ideal since it can fit into any space regardless of the size of the space. In addition, it has 60% more surface area but with the same cross-sectional area, which limits the skin effect at higher frequencies that leads to efficient performance.
Flat wire has higher energy storage, higher thermal efficiency, and limits the skin effect at higher frequencies. The downside of flat wire is its cost and being less available.
Litz wire is made of several tiny strands of wire that have been woven together in a specific pattern. It is a very flexible wire that is easy to use and commonly used for high frequency plug-in transformers. Unlike flat wire and round wire, Litz wire seldom suffers from the skin effect. It is available in a wide range of sizes that are differentiated by the number of stands (N) and the American Wire Gauge (AWG or XX).
There are eight common forms of Litz wire numbered type 1 to type 8, which vary in their structure, method of twisting, insultation, and other factors.
Plug-in transformers are specifically designed to be low energy devices with a secondary winding that has an impedance, resistance to electrical current flow, that is higher and helps limit current flow to a load. For safety purposes, plug-in transformers are double insulated, making them safe to use if there is not a protective ground present.
The National Electric Code (NEC) defines a plug-in transformer as a portion of a system that is between the load and power source and is connected to a piece of electrical equipment. The power limitations of plug-in transformers make them safe from causing fires as well as providing protection from power spikes and power surges. Plug-in transformers are designed and constructed with high impedance, which is why they are able to offer protection for low energy devices.
The use of wall plug-in transformers is important for the protection of low voltage devices that could be damaged by higher voltages. The design of plug-in transformers removes the need for various cooling methods since electronics can overheat during use. This factor makes it possible for manufacturers to produce smaller, lighter, and intricate devices with sensitive circuits.
The main factor for audio plug-in transformers is their impedance, which is provided to microphones, amplifiers, loudspeakers, and recording equipment. Impedance is measured in Ohms, the measure of resistance between two points of a conductor. When the impedance of a plug-in transformer is high, the measure of Ohms is high and the amount of interference in a speaker or headset is lower. Headsets that are used to listen to music around the house have low resistance at 30 Ohms. Professional sound engineers have headsets with high resistance at 300 Ohms.
Plug-in transformers efficiently match impedance levels for audio equipment for efficient power transfer without any distortions or overloads. The key factor is the avoidance of distortions especially in cases where music is being recorded or being projected through speakers.
In the early days of international travel, when Americans were mainly going to Europe, travelers were shocked at the different electrical sockets they found in different countries. At the time, such differences were inconsequential since electrical devices such as computers and cell phones had not been invented. As the number of electronics have rapidly grown, it has become necessary for international travelers to be prepared of the different types of electrical supplies and socket types that are found in foreign nations. This is especially necessary for computers that can be damaged by the higher levels of output found in foreign countries, which can be up to 240 VAC.
International plugs are classified by types with certain types being used in different countries. England uses type G plugs while Denmark uses types C, E, F, and K. A very common form of tour of Europe is to land in London and cross the English Channel by ferry to the Netherlands to begin a tour of the continent. Describing such a trip using sockets and voltage types, in England, a power source is 230 VAC and requires a type G plug-in transformer. When the ferry lands in the Netherlands, the voltage remains the same but the type of plug-in transformers changes to types C and F.
Plug-in transformer manufacturers are very aware of the challenges of traveling internationally and provide safe and reliable transformers that have interchangeable input plugs. This makes it possible for a traveler to immediately adapt to the power supply of a country.
The purchase of highly sensitive technical equipment involves a huge investment that can be destroyed with the use of the wrong type of power supply. Plug-in transformers have been used for years to protect sensitive electronics and enhance their power supply. They smooth power disturbances and reduce electrical noise that can diminish the performance of sensitive devices. In essence, plug-in transformers clean up power delivered from in-home and office outlets.
Technological devices can malfunction or be damaged when the power they receive is inconsistent with the power they require for their operation. Medical equipment, computers, and audio systems necessitate the transforming of power for their proper operation. Plug-in transformers, designed to step down power input, work as a valuable tool to protect sensitive devices and ensure their safe operation.
Electric transformers are static electrical machines that transform electric power from one circuit to the other without changing the frequency. An electrical transformer can increase or decrease the voltage with...
Power transformers are electrical instruments used in transmitting electrical power from one circuit to another without changing the frequency. They operate by the principle of electromagnetic induction. They are used in transmitting electrical power between...
An electrical transformer is a passive machine that transfers electrical energy from one circuit to another using a magnetic flux to induce an electromotive force. Transformers are used to increase (step-up) or decrease (step-down) voltages without changing the frequency of the electric current...
A toroidal transformer is a type of electrical transformer constructed with a torus or donut-shaped core. Its primary and secondary windings are wound across the entire surface of the torus core separated by an insulating material...
Electronically operated equipment depends on power transformers to convert electrical currents into voltage. Current transformers store and transport energy through power lines and grids...
Power supplies are electrical circuits and devices that are designed to convert mains power or electricity from any electric source to specific values of voltage and current for the target device...
An AC power supply is a type of power supply used to supply alternating current (AC) power to a load. The power input may be in an AC or DC form. The power supplied from wall outlets (mains supply) and...
An AC power cord is a detachable way of providing an alternating current of electric energy from a mains power supply to an electrical appliance or equipment. Serving industries like...
A DC DC power supply (also known as DC DC Converter) is a kind of DC power supply that uses DC voltage as input instead of AC/DC power supplies that rely on AC mains supply voltage as an input...
A DC power supply is a type of power supply that gives direct current (DC) voltage to power a device. Because DC power supply is commonly used on an engineer‘s or technician‘s bench for a ton of power tests...
An electric coil, or electromagnetic coil, is an electrical conductor that contains a series of conductive wires wrapped around a ferromagnetic core that is cylindrical, toroidal, or disk-like. Electric coils are one of the simplest forms of electronic components and provide...
Electrical plugs, commonly known as power plugs, are devices responsible for supplying and drawing current from a receptacle to the circuitry of an electrical appliance...
By definition a power supply is a device that is designed to supply electric power to an electrical load. An electrical load refers to an electrical device that uses up electric power. Such a device can be anything from...
Inductors are passive two terminal components of an electric or electronic circuit that are capable of storing energy in magnetic form. They oppose sudden changes in current and they are also called coils or chokes...
A NEMA connector is a method for connecting electronic devices to power outlets. They can carry alternating current (AC) or direct current (DC). AC current is the typical current found in homes, offices, stores, or businesses...
A power cord is an electrical component used for connecting appliances to an electrical utility or power supply. It is made from an insulated electrical cable with one or both ends molded with connectors...
A programmable power supply is a method for controlling output voltage using an analog or digitally controlled signal using a keypad or rotary switch from the front panel of the power supply...
A solenoid coil is a common electrical component that uses a wire that is tightly wrapped around a core, usually made of metal, to generate an electromagnetic field. When an electrical current is passed through the coil, the electromagnetic field that is created provides energy for linear motion...
A voice coil is a winding of a wire, usually copper, aluminum, or copper-clad aluminum that is wrapped around a former (often called a bobbin) and then attached to the apex of a speaker cone...
Thomas Edison developed the power distribution system in 1882. He wrapped a copper rod in jute, a soft shiny fiber from plants, as an insulator. The jute wrapped copper rod was placed in a pipe with a bituminous compound...