Solid-State Isolators Promise Advantages Over Optical-Based Relays

It's tempting to rely on the tried-and-true when selecting components for electronic applications. Familiarity with existing options, lower costs of older technology, or hesitancy to take on new integration challenges can be deterrents to adopting new options. But when considering newer solid-state isolator (SSI) technology over alternatives, product designers might also want to consider the "pay me now or pay me later" equation.

In early 2024, Infineon Technologies introduced a new product family of solid-state isolators (SSIs) (Figure 1) that use coreless transformer technology to support 20 times greater energy transfer, more reliable circuit switching, and protection features not available with optical-based solid-state relays (SSRs). They also promise a 40% lower turn-on power and other benefits compared to electromagnetic relays (EMRs).

Figure 1: The Infineon iSS120R02H, one of the company's solid-state isolators, is based on coreless transformer technology and is used in solid-state relays. (Image source: Infineon Technology)

With these SSIs, developers can create robust custom SSRs capable of controlling loads of more than 1000 V and 100 A. The isolators enable energy transfer across the isolation barrier to drive large MOSFETs and insulated-gate bipolar transistors (IGBTs) without the need for an isolated bias supply to drive the gate.

The long-term benefits and reliability of SSIs can offset the savings of using optocouplers or EMRs. While integrating these devices into applications may have an initial learning curve, that's typically the case with any technological advancement.

More straightforward power design and longer-term reliability are essential factors in customer satisfaction, so engineers should balance bill of materials considerations against long-term costs. The superior performance and current and temperature protection features of Infineon SSIs provide greater reliability and can lower the overall cost of ownership.

With no moving parts characteristic of EMRs, and offering faster-switching speeds and lower power dissipation than optical-based SSRs, Infineon's SSIs provide electronic applications with improved performance, reliability, and better thermal efficiency, minimizing the need for heatsinks. LEDs in optical-based SSRs can degrade over time, while SSIs rely on coreless transformer technology designed to provide greater long-term reliability.

The input side of the Infineon SSIs is 3.3 V compatible and incorporates an integrated power supply buffer capacitor. The supply is based on a shunt regulator that emulates a diode structure. External buffer capacitors are not necessary, although they can be accommodated. They are capable of high output voltage up to 18 V, with no series or parallel configuration required for gate driving.

According to Infineon, their output voltage (V_OUT) is sufficient to drive MOS-controlled transistors, including Infineon's CoolMOS^TM and OptiMOS^TM series power MOSFETs, and their TRENCHSTOP^TM family of IGBTs. Applications can take advantage of advanced output-side control functions, including fast turn-on and fast turn-off, over-temperature protection, and overcurrent protection. All devices in the family were designed to achieve IEC 60747-17 and UL1577 certification.

The Infineon devices can be utilized for customized SSRs in a broad range of high-voltage and high-current applications, from industrial equipment to electrical grids and renewable energy. They can be incorporated into power distribution, power supplies, automatic test equipment, robotics, instrumentation systems, advanced battery management, and numerous other applications.

Infineon's SSI family includes the iSSI30R12H, which comes in a DSO-16-33 package and is tailored for use with CoolMOS™ S7 T-Sense power MOSFETs with an integrated temperature sensor. The input side of the isolator is 3.3 V compatible and operates with a supply current of typically 16 mA.

Other parts in the family for use with external PTC resistors include:

• The iSSI20R02H, the iSSI20R03H, and the iSSI20R11H, all in DSO-8-66 packaging
• The iSSI30R11H, in a DSO-16-33 package

Infineon also offers evaluation boards for the devices in their SSI family. For example, the Eval-iSSI30R12H (Figure 2) includes an iSS130R12H with two CoolMOS™ IPT60T022S7 MOSFETs in an AC switch configuration, with a control interface that can be connected to a pulse generator, a microcontroller, or other digital circuits with appropriate driving capability of at least 25 mA.

Figure 2: The EVAL-iSSI30R12H is one of several evaluation kits for testing switching with Infineon's line of solid-state isolators. (Image source: Infineon Technology)

Conclusion

Infineon's line of solid-state isolators offers important performance, reliability, and thermal management benefits in creating customer SSRs. With no moving parts and greater energy transfer than electromagnetic relays and optical-based SSRs, they provide options for delivering higher-performing and longer-lasting applications that more than justify the initial learning curve.