Signal Transformers

Signal transformers transfer information from one circuit to another by electromagnetic induction. They are used to increase or decrease the voltage from one side of a power transformer to the other. The turn ratio or number of windings on the primary and secondary sides of a signal transformer determines the change in voltage. Devices can have a center tap in the primary side, the secondary side, or both the primary and secondary sides. Products without center taps are also available. Signal transformers are used in applications ranging from audio signal transfers to very high frequency (VHF) data transfers. They often have isolated windings and are used in low-power circuits for impedance matching to achieve maximum power transfer.

There are several types of signal transformers. Audio transformers are designed for voice and data transmissions. They feature a frequency response that ranges from 300 Hz to 20 kHz. Balun (balanced-unbalanced) transformers are used to interface balanced lines to unbalanced lines. Digital transformers are suitable for audio applications because they isolate signals and match impedances. Interface transformers are used in communications applications where the signal is isolated. Isolation transformers completely isolate the primary and secondary windings without affecting the quality of the pass-through signal. Pulse, trigger, and gate drive transformers are used to drive high speed switching devices such as field effect transistors (FETs) and insulated gate bipolar transistors (IGBTs). They are used mainly in switching power supplies. Telecommunications transformers are used in applications that require high bandwidth and fast switching speeds. They isolate the signal between the primary and secondary grounds.  

Signal transformers differ in terms of mounting configurations. Chassis-mounted devices have screw-down tabs. Disk-mounted devices use a simple rubber washer, a metal disc with a hole in the middle, and a sturdy clamping screw. H-frame mounting is used in applications with relatively high levels of shock or vibration. Modular jack designs ensure high common mode noise immunity while maintaining signal integrity. Signal transformers that mount on printed circuit boards (PCBs) use several mounting styles. Surface mount technology (SMT) adds components to a PCB by soldering component leads or terminals to the top surface of the board. Through hole technology (THT) mounts components by inserting component leads through holes in the board and then soldering the leads in place on the opposite side of the board. Flat pack (FPAK) devices have gull wing or flat leads on two or four sides. Connectorized devices attach with coaxial or other types of connectors. Waveguide assemblies consist of a hollow metallic conductor with a rectangular, elliptical, or circular cross-section.  

There are many certification and approval agencies for signal transformers. North American organizations include the American National Standards Institute (ANSI), the Canadian Standards Association (CSA), and Underwriters Laboratories (UL). European organizations include TÜV Rhineland Berlin-Brandenburg and the VDE Testing and Certification Institute. The International Electrotechnical Commission (IEC) prepares and publishes standards for many electrical and electronic technologies. Suppliers that meet U.S. military standards (MIL-STD) are also available.

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Part Numbers for Signal Transformers