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Innovations in isolation - advanced photocoupler technologies enable greater protection in smaller packages

Photocouplers (also known as optoisolators or optocouplers) have become an increasingly important bridge between circuits operating at different voltages.

They provide galvanic separation and prevent the flow of potentially damaging loop currents between grounds at different potentials; or ensure that current or voltage surges do not damage system components or harm users. Optical isolation is also useful for preventing the propagation of electrical noise and eliminating impedance mismatches.

Miniaturisation efforts of optically isolated components are constrained by the need to meet mandatory safety specifications such as IEC 60747-5-5. IEC 60747-5-5 requires minimum creepage and clearance of 5mm to pass functional insulation-voltage tests at 707Vpk, and insulation thickness of at least 0.4mm to satisfy the reinforced isolation specification.

This tends to create challenges for component designers developing optocouplers in ultra-small packages.

Despite limitations, space-efficient internal design combined with surface-mount package technology allows new devices to achieve smaller overall dimensions and lower package height while meeting or surpassing the IEC 60747-5-5 specifications.

The SO6 package has an outline of 7.0mm x 3.7mm x 2.3mm allows isolation voltage of 3750V and maximum operating insulation voltage of 707Vpk. This is ideal for applications requiring insulation performance greater than the 565Vpk of existing surface-mount devices in Mini-Flat SOP (MFSOP6). To achieve comparable insulation performance, designers would otherwise have to use larger SDIP devices that measure 9.7mm x 4.6mm x 4.0mm.

Comparison of insulation performance of SDIP6, SO6 and SO6L packages
Comparison of insulation performance of SDIP6, SO6 and SO6L packages

In addition to improving safety performance within small device dimensions, development of optically isolated devices also targets power savings and longer device lifetimes through enhancements to the integrated LED emitter.

Gallium-arsenide (GaAs) LEDs have proved effective in many manufacturers’ product ranges, and Toshiba is now moving forward by using the latest gallium-aluminium-arsenide (GaAlAs) LED technology in its new device families. These can be driven with low currents, reducing system power consumption and supporting extended LED operating life.

Toshiba has more than 20 devices in its latest SO6 surface-mount package, for applications such as transmitting logic signals and driving intelligent power modules and driving IGBTs and MOSFETs. The range includes Non Zero-Crossing (NZC) and Zero-Crossing (ZC) triac couplers , MOSFET output devices (Photorelays), transistor output devices with AC or DC inputs,  and offers a choice of standard or Darlington outputs.

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·Before creating and producing designs and using, customers must also refer to and comply with the latest versions of all relevant TOSHIBA information and the instructions for the application that Product will be used with or for.