Understanding and Selecting Isolation Transformers

What is an isolation transformer?

Isolation / data transformers are used for isolation and voltage scaling in data line and power supply applications. Isolation transformers typically serve three main purposes:

1. Connecting circuits with grounds at different potentials – to prevent ground loops
2. Galvanic isolation – to prevent the flow of direct current (DC) between sections of circuits
3. Voltage transformation – to step up or step down from one voltage to another

Isolation transformers may be also be described as power-supply transformers, signal transformers, data-line transformers, communications transformers, interface transformers, data-interface transformers, industrial-communications transformers, and miniature transformers. This article discusses isolation / data transformers and the wide range of applications in which Coilcraft off-the-shelf isolation / data transformers can be used.

In what applications are isolation transformers used?

Isolation transformers are very versatile and well suited for many commercial and industrial power supply and data communications applications, including:

• Low voltage (3.3 to 24 V) isolated DC-DC power supplies up to 7.2 Watts
• Low-noise RS-485, RS-422, and RS-232 isolated serial communications data interfaces
• PCMCIA thin card drivers up to 750 mW
• Industrial and building automation and control systems
• Multipoint data transmission systems
• Isolated CAN interfaces
• Isolated 4 – 20 mA current loops for process control
• Transducer and actuator controls
• Data acquisition (DAQ) systems
• Isolated analog to digital conversion (ADC)
• Serial Peripheral interfaces (SPI)
• Inter-integrated Circuit (I²C) interfaces
• Half-bridge, Full-bridge, and Push-pull low voltage isolated DC-DC power supplies

A high noise immunity serial communications standard such as RS-485 is best used in industrial environments. Unlike Ethernet, which has no built-in method of packet collision avoidance, the master / slave topology of RS-485 leads to more reliable behavior by avoiding data packet collisions and maintaining data integrity, which is crucial in noisy industrial environments.

What range of isolation transformers does Coilcraft manufacture?

Coilcraft has a variety of off-the-shelf isolation transformers with:

• Input voltages of 3.3 to 24 Volts
• Power ratings up to 7.2 Watts
• Turns ratios from 1:1 to 1:5
• Volt-time capabilities from 8.64 to 134 Vµs
• Inductance from 16 to 1000 µH
• Isolation from 1500 to 5000 Vrms

How do I select the Coilcraft isolation transformer that best fits my application requirements?

Coilcraft has developed a large selection of isolation transformers for the applications discussed above and in the many IC reference documents listed in the section below.

Find your Coilcraft isolation transformer to match it with the IC for your application.

IC Reference Documents

Maxim Integrated

• Maxim MAX253 Transformer Driver
• Maxim MAX845 Isolated Transformer Driver for PCMCIA applications

Texas Instruments

• Texas Instruments SN6501 Push-Pull Transformer Driver for Isolated Power Supplies
• Texas Instruments ISO35T Isolated 3.3 V RS-485 (full-duplex) Transceiver with Integrated Transformer Driver for up to 1 Mbps
• Texas Instruments ISO3086T driver supports up to 20 Mbps data rates with Coilcraft DA2304-AL isolation transformer
• Texas Instruments ISO1176T Isolated 40 Mbps, 3.3 V to 5 V Profibus Interface with Coilcraft DA2304‑AL

Analog Devices

• Analog Devices ADuM347x Quad-Channel Isolators with Integrated Transformer Driver Evaluation Board (3 isolated 25 Mbps data channels per circuit)
• Analog Devices ADuM4070 Isolated Switching Regulator with Integrated Feedback (CR7983‑CL, etc.)
• Analog Devices ADM2482E Isolated RS-485 Transceivers for up to 16 Mbps with DA2303‑AL
• Analog Devices ADM2485 Half-duplex Isolated RS-485 Transceiver with Transformer Driver for up to 16 Mbps with DA2303‑AL / DA2304‑AL

What's Next?

View more: Getting Started Series