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signal transformers selection guide     signal transformers selection guide    signal transformers selection guide

(left to right) THT transformer | Ethernet isolation connector | Video isolation transformer

Image credit: Schaffner EMC | MPS Industries

 

Signal transformersare used as a step-up / step-down, isolating, or impedance matching component in electronic devices.  Power transformers, which carry current, are generally not suited for use as signal transformers and vice versa. Signal transformers are used in typical electronics applications, including telecommunications, radio frequency (RF), audio, video, and general purpose uses.

 

In general, a transformer consists of two wire coils wrapped around a core; the coils are termed primary and secondary and are separated by a medium such as air, water, or metal. The primary coil is typically connected to a source supplying a current or some other signal. When this signal is applied to the primary coil, it creates and electromagnetic field and induces a voltage in the secondary coil. Based on the number of windings per coil, a transformer can reduce or increase the applied signal, or simply isolate it, depending on the device's construction and intended application.

signal transformers selection guide

A basic transformer. Image credit: BillC

 

Applications

Signal transformers may be used in traditional power transformer applications, such as signal isolation and stepping signals up or down.

  • Isolation prevents signal crossing and current leakage between two circuits. For more specific information about isolation transformers, please visit the Isolation Transformers Selection Guide.
  • Step-up/down - Transformers that step signals up or down are used to match signals between two different circuits or devices. This process is related to impedance matching, described below. Transformers that output a signal identical to the input are known as one-to-one devices. 
  • Impedance matching is used to match impedances between two different devices, such as a speaker and an amplifier. If the impedance varies, the signal will become distorted and its quality will deteriorate.
  • Lighting transformers are used to provide suitable power to lights and lighting systems.
  • Inverters are used in inverter circuits, such as power conversion inverters.

Other signal transformer uses include medical applications, as switch mode devices in power supplies, and telecommunications use.

 

Signal Transformer Types

Signal transformers can be classified primarily by the type of signal they carry.

  • Audio transformers are used for voice and data transmissions with receivers, amplifiers, speakers, and audio cables. They typically operate on frequencies from 300 Hz to 20 kHz.
  • Baluns are used to convert a balanced signal - comprised of two signals working against each other - to an unbalanced one, or a single signal working against a ground. Like impedance matching transformers, baluns are used to gain compatibility between two different systems or devices. They are commonly found in radio, television, video, and audio applications; they may also match impedance in all of these uses.
  • Digital transformers carry signals comprised of discrete values, as opposed to analog signals of continuous functions. They are frequently used in audio applications to isolate signals or match impedance.
  • Electronics transformers refer to current or voltage transformers used to test electronic devices.
  • RF transformers carry radio frequency (RF) signals ranging from about 3 kHz to 300 GHz. RF transformers are typically low-power devices used for impedance matching.
  • Telecom / LAN transformers are typically used for isolation and may feature high bandwidth and fast switching speeds.

Form Factor

Signal transformers may also be classified based on their mounting or form factor.

  • Chassis mount transformers are screwed directly to an instrument chassis using tabs and fasteners.
  • Chip transformers are integrated circuit (IC) chips manufactured using thin film technology. Signal transformers are far more likely to be found in chip form when compared to power transformers.
  • Dish mount devices are secured to a chassis or other flat surface using a simple rubber washer and a metal disk. A hole in the middle of the disk allows the transformer to be screwed down.
  • Modular jacks typically take the form of an RJ-45 form factor and are ideally suited to signal transformers.
  • Printed circuit board (PCB) mounting is common in signal transformers. More information about PCB mount devices is found below.

Package Type

Many signal transformers are either semiconductor chips or are PCB-mounted modules. The main types of packaging are:

  • Connectorized transformers attach to PCBs and other devices using electrical connectors.
  • Flat pack (FPAK) transformers mount using leads - gull wing or flat - found on two or four of the device's sides. FPAK devices are often surface-mounted ceramic devices with excellent thermal and electrical performance.
  • Surface mount (SMT) devices feature a flat pad surface which is soldered onto a PCB. SMT is a newer technology which has largely replaced through-hole (THT) mounting, and has enabled smaller components, simpler and faster automated assembly, and better electrical performance and mechanical vibration resistance.
  • Through hole technology (THT) devices have relatively long leads which are fed through holes in a PCB and soldered to the opposite side of the board. While THT products are capable of stronger mechanical connections when compared to SMT devices, THT drawbacks include increased cost of drilling holes and the inability to produce smaller components.

signal transformers selection guide    signal transformers selection guide

SMT leads (left) and the longer THT leads. Image credit: Custom Electronics | Shutterstock

 

References

 

Bill Whitlock - Audio Transformers (pdf)

 

N.H. Crowhurst - The Matching Transformer


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