New Industry Products

Coreless Transformers Improve Solid-State Isolator Response

February 28, 2024 by Mike Falter

Infineon’s family of solid-state isolators features a coreless transformer capable of delivering faster and more reliable switching and protection features unavailable in optically isolated devices.

At APEC in Long Beach, California, today, Infineon Technologies AG released a family of solid-state isolators (iSSI) using coreless transformer (CT) technology to improve switching speeds and reliability and incorporate protection capabilities not found in optically based solid-state relays (SSRs).   

The isolators are well suited to pair with Infineon’s OptiMOS low- and medium-voltage power MOSFETs and CoolMOS high-voltage superjunction MOSFETs for a switching solution with better response times and reduced power dissipation.

Applications for the isolated drivers include battery management, energy storage, renewable energy, and industrial and building automation systems. 


Signal isolation for renewable power generation systems

Signal isolation for renewable power generation systems. Image used courtesy of Infineon


Signal Isolation in High Voltage Systems

Solid-state isolators and relays are commonly used in high-voltage power conversion systems, such as solar inverters, to pass control signals across the isolation boundary between the low-voltage control and high-voltage power circuitry. 

Traditionally, optically isolated SSRs use light-emitting diodes and photodetectors to optically communicate digital or analog control signals across a high-voltage boundary without compromising system isolation. Isolation is manifested through the physical separation (creepage or clearance) between the optical components.  


Solar microinverter requires control signal isolation

Solar microinverter requires control signal isolation. Image used courtesy of Infineon


Coreless Transformer Isolation

According to Davide Giacomini, marketing director for Infineon’s Green Industrial Power division, at Infineon coreless transformer technology is a real “game-changer” for solid-state switching applications, allowing for on-resistances as much as fifty times lower than comparable optically isolated solutions. The CT isolators also offer much greater energy transfer capabilities and incorporate current and temperature protection capabilities not available in optical devices.

Infineon’s coreless transformer technology is magnetically coupled, galvanically isolated coupler technology. The coreless transformer is constructed using a semiconductor manufacturing process that forms the transformer using two metal spirals etched into the silicon and separated by silicon oxide insulation.


Magnetically coupled coreless transform technology       

Magnetically coupled coreless transform technology. Image used courtesy of Infineon


A well-defined complementary metal-oxide-semiconductor process allows other functional blocks, like input filters, to be integrated on-chip with the transformer for a complete integrated circuit solution. 


Driving a MOSFET in a Solid-State Relay

For a solid-state relay constructed with a CT-isolated gate driver, the microcontroller relays its switching commands to the driver inputs in either an inverting or non-inverting mode. Input filters process the signals to eliminate unwanted switching from spurious interference.  

The transmitter block (TX) converts the logic signals received at the input into an RF carrier signal. This RF signal is then transmitted across the transformer and converted back to the original logic signal by the receiver unit (RX), which passes the digital command signals to the gate driver switches (Q1 and Q2) to turn the power switch on or off.


Driving a MOSFET with a CT-isolated driver

Driving a MOSFET with a CT-isolated driver. Image used courtesy of Infineon


Switching Signal Response Time

A key performance criterion for isolated drivers and relays is response time and signal propagation delay from input to output. Solid-state isolators using CT technology allow fast response times with reduced signal propagation delays, yielding more efficient switching and better system performance.  


Propagation delays in an isolated FET driver application.

Propagation delays in an isolated FET driver application. Image used courtesy of Infineon


For gate drivers using CT technology, the limiting factor for propagation delay is the input filtering, not the transformer itself. This differs from optical gate drivers, where the optical circuitry defines the signal propagation delay.