How to Select Signal Transformers
(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.
A basic transformer. Image credit: BillC
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.
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.
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.
SMT leads (left) and the longer THT leads. Image credit: Custom Electronics | Shutterstock
Related Products & Services
Audio transformers improve sound quality by removing interference from audio signals.
Current Sense Transformers
Current sense transformers are used to detect and measure current. There are two basic types of products: switch-mode transformers for power conversion applications, and precision-measurement transformers for instrumentation applications.
Gate Drive Transformers
Gate drive transformers are used to modify the voltage level to a gate. They also provide impedance matching and voltage isolation.
RF transformers transfer energy from one circuit to another by electromagnetic induction. Typically, they are used to increase or decrease voltage as it passes from one side through the other.
Switch Mode Transformers
Switch mode transformers (switching transformers) are used mainly in switching power supplies and DC-DC converters. They provide a storage element for transferring energy from input to output in discrete packets as required in switching power supplies, regulators and converters.
Telecom transformers are used in applications which require high bandwidths and fast switching speeds. They isolate the signal between primary and secondary grounds. This product area includes DSL, xDSL, T1, E1, ISDN, LAN, WAN, Ethernet, ATM and modem transformers.
- Audio Transformer
- Balun Transformer
- Chassis Mount
- Chip Transformer
- Current Sense Transformer
- Digital Transformer
- Dish / Disk Mount
- Electronics Transformer
- Encapsulated Transformers
- Flat Pack (FPAK)
- Flyback Transformer (FBT)
- High Frequency Transformer
- High-Voltage Transformer
- Interface Transformer
- Inverter Transformer
- Isolation Transformer
- Medical Transformer
- Modular Jack
- One to One
- Transformer Types / Applications:Other
- Mounting / Form Factor:Other
- Package Type:Other
- Standards / Compliance:Other
- PC / PCB Mount