The expanding demand for electronic equipment is fueling the need for more high frequency transformers. At Agile Magnetics, we have been designing and manufacturing these products since our company began in 1992. Our experience encompasses high frequency transformers constructed of all different materials, manufactured to our customers’ precise specifications, and consistently delivered on time.
Today’s electronics demand powerful transformers that fit into the most compact applications. Any piece of equipment that runs on transformers that is poorly designed runs the risk of breakdowns and failure. Our transformers are custom designed and manufactured to safely and efficiently deliver the highest power levels, decreasing the risk of skin effect losses and hysteresis.
As digital electronics become part of an ever-increasing number of devices, the need for high frequency transformers continues to grow. The following represent just a few applications associated with these transformers:
· Personal electronics
· Industrial equipment
· Solar converters
· Electric drives
· Energy conversion
High-Frequency Transformer Design
While they operate on the same principles, the fundamental difference between high-frequency transformers and standard transformers is their voltage capacity. Rather than the typical 50 or 60 Hz of line voltage transformers, high-frequency transformers can tolerate much higher voltage frequencies, often from 20 kHz to more than 1 MHz.
High-voltage transformers offer numerous advantages, such as:
· Highly customizable by application
· Smaller design requires less materials
· High power density
Alongside these benefits, however, skin effect and proximity effect must be carefully managed to create an effective high-frequency transformer. Skin effect losses occur when high-frequency currents flow onto the surface of conductors. Proximity effects occur when magnetic fields from nearby conductors cause interference in the current flow.
To address skin effects, proximity effects, and other design issues, consider the following factors:
· Litz Wire
Proximity and skin effect issues can be addressed using Litz wire. Litz wire bundles thin copper wires into a braided or twisted configuration that minimizes skin effect by forcing current to travel more evenly throughout the wire. The design of Litz wire and the even current flow it provides also minimize interference from other nearby conductors, which mitigates the proximity effect interference and enables very high frequency current flows for transformers.
· Air Gaps
It is also important to reduce gap amounts and size in the transformer’s core. Air gaps allow magnetic fields to expand, contributing to proximity effects by interfering with the nearest transformer. Tape and clever construction designs can help minimize air gap problems, keeping proximity effects to a minimum.
· Core Material
When choosing a high-frequency transformer design, the transformer’s data book provides excellent tables that can facilitate selection of the appropriate core based on your calculations. Though air-cores exist, the most typical core for a high-frequency transformer will be composed of the powdered iron substance known as ferrite.
Ferrite cores combat many of the ill effects that plague high-frequency transformers. They experience very low core losses and lose very little to eddy currents. When choosing the core, it is also possible to begin with a core-weight or core-volume based on the transfer power and switching frequency and choose which core will be most appropriate in that manner.
Small, dense transformers require continuous cooling to keep the system from overheating. Designing small transformers with a cooling plate or fan has become necessary for a variety of applications. The transformer may also be potted in a thermally conductive material to dissipate unwanted heat.
Once the appropriate core is chosen, designers calculate the primary number of turns for the transformer. Since the term "high frequency" spans a wide variety of frequency levels and the particular use may or may not need to accommodate certain ranges. Knowing the number of turns determines the magnetic flux density present in the core. Finally, the wire-diameter is calculated, based on the current for both the primary coil and the secondary coil. With all of these factors, a topology can be chosen, and the design takes shape.
Some high-frequency transformers must also accommodate higher voltages in order to provide the needed conversion of voltage. High-voltage transformers typically convert voltages from a higher to a lower voltage, going down a level or changing the phase configuration. This is accomplished through magnetic induction between coils.
Single-phase and three-phase primary configurations of high voltage transformers are commonly used . When identifying the appropriate specifications for your high voltage transformer, you'll need to evaluate:
· Maximum secondary voltage rating
· Maximum secondary current rating
· Maximum power rating
· Output type
When choosing output, you’ll have both alternating current (AC) and direct current (DC) options. While AC will typically be given in RMS values, you'll want to discuss with your designer about the type of rectification for DC.
Options also include toroidal and laminated transformers. Toroidal is characterized by copper wire surrounding the magnetic flux core. Laminated transformers instead rely on a steel core with a non-conductive varnish to reduce the potential losses. High voltage power transformers come in many types, so consult your designer about how a high voltage transformer can apply to specific requirements of your application.
Custom High-Frequency Transformers
The requirements placed upon transformers may vary widely, and a standard solution may not be right for every application. Agile Magnetics provides has the capability to design custom high-frequency transformers with a range up to 500 kHz. However, the frequency is not the only thing to consider when customizing a transformer.
Equipped with an advanced 40,000 square foot facility and a full fleet of state-of-the-art equipment, our team designs and manufactures any type of standard or high frequency transformers our customers require. When designing custom high-frequency transformers, a variety of topologies are available, including:
- Buck Transformers: The simplest and cheapest design, buck transformer topology can be right for DC applications that simply need to step down voltages. You'll likely need output filters to compensate for voltage ripple.
- Boost Transformers: Also simple in design, boost topology steps up a voltage rather stepping it down. It is simple in design and non-isolating.
- Buck-Boost Transformers: Battery powered applications with the potential for varying input voltages will benefit from a combination buck-boost transformer, which can voltages up or down as required. Voltage ripple must be reduced with input filters.
- Fly-Back Bias Transformers: This transformer boasts a simple design. Easily handling more than one output, fly-back bias transformers can accommodate positive and negative voltage on one transformer. As a result, it is widely used for switch mode designs. These transformers provide a range of benefits including decreased inductance leakage and decreased noise in some applications.
- Forward Converter Transformers: Among the most popular on the market today, forward converter transformers are more complicated than fly-back models, but feature exceptional levels of efficiency. Forward converter transformers are appropriate for both large and small applications, though they are often popular in laptops, cellular phones, and power sources for LED lights. They can have a variety of input voltages, both higher and lower than output voltages.
- Full Wave Transformers: In half-bridge power circuits, full wave transformers bring an exceptional level of isolation. These transformers are essential in applications involving an electronic switch device.
- Push-Pull Transformers: Resembling buck boost transformers in both design and functionality, push-pull transformers allow for multiple DC output voltages and apply power directly to the load. Also known as push-pull converters, these transformers are distinguished by pairs of transistors that oscillate on and off in order to reverse the current. Cost-effective and compact, they see frequent use in high power transformer
- applications. These uses can vary from industrial lighting, automotive, telecommunications, and computers.
- Gate Drive Transformers (GDTs): Well known for combining reliability with exceptional isolation, gate drive transformers are heavily used for applications such as half-bridge power circuits. They also turn semiconductors on and off, including IGBTs and MOSFETs. An important function of these transformers is to drive the gates of electronic switching devices.
- Resonant Converter Transformers: Resonant converters are adept at handling high voltages and working at radio frequencies. Designed with ferrite and air cores, they are often found in engines, radio receivers, and transmitters.
- High Voltage, High Frequency Transformers: These transformers are designed to handle up to 15,000 volts safely and accurately, converting high voltage and current levels between coils by magnetic induction. High voltage, high frequency transformers are relied on for applications ranging from power supplies to laser equipment and particle accelerators.
- Universal Winding Transformers: Also highly advantageous for high voltage applications, universal winding transformers feature a design with an increased coil build. This provides more space between the turns, allowing freer penetration of dielectric oil onto the coil. More oil not only creates additional isolation, but also creates much reduced chances of arcing and corona.
- Pulse Transformers: Designed to produce right-angle pulses, pulse transformers help to balance electrical signals, and separate AC components at a signal.
- Isolation Transformers: All transformers feature some properties of isolation, regardless of their primary applications, but only isolation transformers are designed explicitly to isolate the primary from secondary windings to meet safety agency requirements.
Agile Magnetics can customize all of the above options to meet unique challenges of specific applications. We also provide all sizes, including:
· Pot core
We can also custom-design standard low-frequency transformers if your application poses low risks for skin effect, proximity effect, or has less need for cooling. We also offer a wide range of high-frequency inductors.
Applications of High-Frequency Transformers
High-frequency transformers, with their small size, can be valuable in a wide range of large or small applications. Frequent applications include, but are not limited to:
· Consumer electronics.
· Renewable energy (solar inverters)
· Motor drivers
· Battery chargers
· Railway (train electrical power)
High-frequency transformer selection involves the careful consideration of all design elements to ensure your transformer functions seamlessly in in its intended application. As innovation in electronic devices continues and industries demand increasingly higher, the design process for transformers becomes integral to the creation of a product with high reliability and excellent power flow.
Agile Magnetics has provided the industry’s highest quality transformers to global customers for over 23 years. The ever-growing demand for high frequency applications has created new opportunities to serve customers with the finest quality transformers available. To find out more information or request a quote, please contact us today.
This free eBook takes a look at the principles and calculations associated with transformers and the critical components of supplying power to modern electronics.