Transformers Information

Transformers are electrical devices that are designed to transfer energy from one circuit to another by electromagnetic induction. They are used typically to increase or decrease voltage as it passes from one side of the device through the other. The turn ratio, or the number of windings on the transformer’s primary and secondary sides, determines the change in voltage. There are two major transformer categories: power transformers and signal or radio frequency (RF) transformers. As their name suggests, power transformers are designed to provide power to the power supply of electronic devices. They convert one voltage to another at a specific power level. Signal transformers or RF transformers are designed to transfer information from one circuit to another. Generally, their power level is low. 

There are many application-specific transformer types. For example, audio transformers are designed for voice and data transmissions. Autotransformers have only one winding and are used mainly for low-power applications. Balun transformers are used to interface a balanced line with an unbalanced line. Bar transformers or bar current transformers are a type of toroidal transformer with a bus bar. Buck-boost transformers can make small changes to a voltage. Cast coil transformers have windings that are solidly cast in resin under a vacuum in a mold. Constant current transformers or current regulators are designed to deliver constant current under varying loading conditions. Current sense transformers, as their name suggests, as used to detect (sense) and measure current. 

Specific types of transformers include digital transformers, distribution transformers, electronics transformers, flyback transformers (FBT), and generator step-up transformers. Digital transformers are used in audio applications for signal isolation and impedance matching. Distribution transformers are pole-mounted transformers that supply relatively small amounts of power to residences. Electronics transformers are current or voltage transformers that are used as measurement instruments in the electronics industry. Flyback transformers (FBT) or line output transformers are used to produce a very high output voltage from a relatively low input voltage. Generator step-up (GSU) transformers are a type of power transformer for increasing the voltage from a power generator to a desired higher voltage.  

Transformer types include harmonic mitigating transformers, high frequency transformers, high voltage transformers, impedance matching transformers, industrial control transformers, and interface transformers. Inverter, isolation, leakage, lighting, medical, multi-ratio, neutral grounding, and planar transformers are also available. Other types of transformers include pulse, rectifier, resonant, single phase, solar power, substation, switch mode, telecom or local area network (LAN), three-phase or polyphase, and trigger or gate drive. Variable autotransformers or variacs have a sliding tap. 

Performance specifications for transformers include operating frequency range, maximum primary voltage rating, maximum secondary voltage rating, power rating, and operating temperature. Mounting styles and form factors are designated as chassis mount, chip transformer, dish or disk mount, H-frame, modular jack, pad mounted, printed circuit board (PCB) mounted, and pole mounted. Choices for winding turns include step-up, step-down, variable, and one-to-one. Transformers that meet national, international, regional, and regulatory standards for safety and performance are commonly available. For example, in the European Union, transformers must comply with RoHS and WEEE.

• Wideband Transformers
  . Application Note # 151. Wideband Transformers. Wideband transformers couple signals magnetically from. equal to (R /R )1/2 and the transformer secondary. L. S. input to output terminals with optimum transmission fidelity. terminated in R , the transformer input impedance equals. L. over broad frequency...
• Transformer Theory
  magnetic field will produce a current in the secondary. A transformer consists of at least two sets of windings wound on a single magnetic core. There are two main purposes for using transformers. The first is to convert the energy on the primary side to a different voltage level on the secondary side...
• The Importance of Effective Transformer and Control Transformer Protection (.pdf)
  The importance of effective transformer and control transformer protection cannot be over emphasized. After motors, transformers are typically the second most common application where proper overcurrent protection is required and utilized to provide the necessary protection to facilities...