SSRs Challenge Electromechanical Relays in High-rel Designs

Apr 13, 2005 5:31 PM

International Rectifier has introduced a series of hermetically sealed radiation-hardened (rad hard) solid-state relays (SSRs) for high-reliability applications. By replacing existing electromechanical relays, the RDHA7x SSRs improve reliability in power bus switching, heater control circuits, battery charging and other hi-rel applications. The new SSRs are available in single, dual or octal SPST NO (single pole, single throw, normally open [Form A]) type with current ratings of 1.5 A to 20 A at 60 V to 100 V.

“Solid-state relays have switching times that are similar to electromechanical relay switching times, but are immune to vibration and shock, increasing reliability. Also, because they have no contact bounce, filters can be removed from the system, reducing size and weight. The new SSRs have buffered inputs, so they can be driven directly from logic circuits, simplifying overall design and reducing parts count,” said Rick Furtney, International Rectifier vice president, Hi-Rel Sector Business Unit.

In the past, SSRs may not have been able to achieve sufficiently low values of on-resistance to be acceptable in the target, high-rel applications. However, improvements in low-voltage MOSFET technology have sufficiently lowered R_DS(ON) so that low-voltage MOSFETs can now be used as building blocks in SSRs capable of replacing electromechanical relays. IR’s current generation of low-voltage MOSFETs feature R_DS(ON) as low as 20 mΩ. To complete the SSRs, the MOSFETs are combined with optoisolators and other components in wirebonded, hybrid assemblies. Along with better reliability, the SSRs offer switching rate control, reducing system requirements for RFI/EMI filtering.

The RDHA7x series initially includes four devices. The first SSR is the RDHA710SE10A2Q (SMD mount) dual SSR, with current handling capabilities of 20 A (10 A when properly derated) and a breakdown voltage of 100 V, which is high enough to allow normally applied derating.

The second and third devices are the RDHA701FP10A8Q and the RDHA701FP10A8C, containing eight SPST, normally open, 1.5-A, 100-V SSRs. These chips feature selectable input actuation methods and a choice of rise/fall time control. They are housed in a 64-pin surface-mount package. The fourth SSR is the RDHA720SF06A1N, a single 20-A, 60-V device in an SMD package. Most of these devices also are available in alternate style packages for flange mounting.

The new devices are characterized for total dose levels of up to 100k rad (Si) or higher, and single event effects (SEE) immunity up to an linear energy transfer (LET) of 37 MeV/(mg.cm²) or higher. Isolation is 1000V I/O. Class “P” (Unscreened), “H” and “K” screening is available, see data sheet.

Radiation-hardened MOSFETs represent a special niche in the world of discrete semiconductors. Though several companies may have devices that can meet the total dose requirements for rad-hard components, these parts may fall short when it comes to single-event requirements. Single-event specifications are challenging because they represent particularly highly levels of radiation.

Available now, the SSRs are priced starting at $1122 each for the RDHA710SE10A2Q (unscreened) in 100-piece quantities.

For more information, visit www.irf.com.

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