LH1500

Siemens Solid State Relays (SSRs) are miniature, optically-coupled relays with high-voltage MOSFET outputs. The relays are capable of switching ac or dc loads from as little as nanovolts to hundreds of volts. Likewise, the relays can switch currents in the range of nanoamps to hundreds of milliamps.

The MOSFET switches are ideal for small signal switching and are primarily suited for dc or audio frequency  pplications. Siemens offers integrated current limiting on many of its relays. If load current through the relay exceeds the rated value, the relay clamps the current at a predefined value. If the excessive load current persists, the limiting circuit has a foldback feature to minimize relay power dissipation.

The current-limit circuit has a multitude of uses. It can be used in telephony to clamp excessive currents emanating from lightning strikes and/ or power-main crosses or in instrumentation and industrial application to squelch transients from reactive loads. The current-limit circuit also provides short-circuit protection in power-feed applications.

The SSRs feature a monolithic output die that minimizes wire bonds and permits easy integration of high-performance circuits such as current limiting in normally-open switches. The output die contains all the necessary circuitry to perform a relay function, including the photodiode receptor array, turn-on and turn-off control circuitry, and the MOSFET switches. The optically-coupled input is controlled by a highly efficient GaAlAs infrared LED.

Siemens SSRs are available in a 6- or 8-pin through-hole DIP or in gullwing surface-mount packages. Some parts are also offered in 8- or 18-pin small-outline packages (SOPs). The SOPs are size and height compatible with PCMCIA Type 2 cards. A 0.4 mm distance through insulation spacing is also available on "H" suffix coded parts. Refer to the Parts Coding section for a more in-depth description of these parts.