Relay race uncovered Steve BushIn 1835 Professor Joseph Henry of Princeton University first demonstrated the electromagnetic relay, then Samuel Morse improved it, and it has been with us ever since - arguably the oldest electronic component.
That the traditional relay has not been completely overtaken by semiconductor devices is a tribute to its versatility, and steady size reduction through innovation.
Purely electronic relays exist and can offer advantages over their electromechanical cousins in some circumstances.
Perhaps the most dramatic size-reduction in electromechanical relays has occurred through adoption of so-called fourth-generation construction.
Axicom, part of Tyco Electronics, recently released fourth-generation relays suitable for Pb-free soldering processes with temperatures up to 255°C. Improved high-temperature resistance comes mainly from better plastic parts which hold their shape and do not produce contact-contaminating gasses.
Called the IM series, the double-pole change-over relays are aimed at telecoms and signal switching. They are a minute 10x6x5.65mm and can switch resistive loads up to 2A (Max: 60 W, 62.5VA, 220V DC, 250V AC).
Coil variants from 1.5 to 24V are available, coil consumption is between 140 and 200mW and latching and non-latching versions exist. In common with relays of this size from several manufacturers, three different terminal options are available: through-hole (TH), gull-wing surface-mount (SMD) and J-lead SMD.
Omron recently launched a series of single-pole single-throw miniature low-profile relays for high-density PCB mounting. The G6L family measures 7.0x10.6mm with a 4.2mm high SMD versions and 3.8mm TH version. Contact resistance is a nominal 100mΩ, operating time is 1.1ms (5ms max), and release time is 0.4ms (5ms max). The relays are Pb-free and conform to UL60950 and CSA22.2 (UL & CSA certified).
3, 4.5, 12 and 24V DC coils are available to suit applications in modems, PC peripherals, phones, office equipment, test gear and security systems. It is not only low-power signal relays that have shrunk. Power relays have also benefited from advances in design.
Omron's recently introduced G8NW is specifically for reversing electric motors in automotive applications. Despite its 15.7x14.3x13.5mm size, "ideal for mounting inside car door skins", says the company, and 8g weight, it can switch 30A at 12V.
Standard or supersensitive versions are available, having coil resistance 225( and 180( respectively.
Schrack, another part of Tyco, has added a high in-rush version of its 2-pole RT relay. The 29x12.7x15.7mm RT2 handles 8A DC normally but is capable of switching 45A in-rush for a 230V AC, 1100W lighting load. The company sensibly provides a series of maximum in-rush figures for different difficult loads representing typical applications. Foreseen applications include automotive, emergency lighting, domestic appliances and heating controls.
RT2 is supplied to environmental standard IP40, with IP67 sealing on request. Also new from Schrack is its 40x1x16mm SR 4M safety relay which features forcibly guided contacts to EN 50205.
This is a reduced version of the company's SR6 6-pole device. It has 8A (200VA) 4-pole contacts with either: three normally open and one normally closed contact; or two normally open and two normally closed contacts. RF relays have been available in tiny TO-5 packages for decades. Now Matsushita has released a TO-5-alternative in the shape of its 5GHz 50Ω RJ type.
Measuring 14x9x8.2mm, it is available in SMD and TH options, both fully sealed and operating from -30 to +70°C. Claimed performance of the double-pole change-over device at 5GHz is 35dB minimum isolation, maximum 0.5dB insertion loss and VSWR under 1.25.
Mono-stable and latching coils are available at voltages from 3 to 24V DC. Application in instrumentation and measurement, including in medical devices, is expected. Matsushita relays are sold under NAiS and Sunx brand names. Over in the fully-electronic camp, Omron has added G3VM-61G to its G3VM range with a view to under-cutting reed relays in applications including ATE, data acquisition and security systems.
Typical on-resistance of its Mosfet output is 1Ω, and it comes in a 2.1x3.9x4.4mm SOP-4 pin package. Up to 400mA at 60Vpeak can be switched. Typical operating time is 0.6ms with a 0.1ms release time. TH and gull wing types are available.
Matsushita has this week launched its slim-line (4.5mm thick) AQG single-in-line series of solid-state relays. The devices are rated to switch 1A and 2A loads at voltages ranging from 75 to 264V AC. The series is available with zero crossing detection as an option and are all fitted with an integral snubber "to prevent malfunction and miss operation caused by fast rising voltage spikes on the output side". Isolation between input and output is 300Vrms. The drive can be either 5, 12 or 24V DC.
Typical applications, says Matsushita, are in manufacturing equipment including numerically controlled machines, injection moulders and assembly robots. With arguably the highest current to volume ratio yet, International Rectifier late last year introduced its 8.6x10.0x3.4mm PVN013 which can switch 4.5A DC and 2.5A AC/DC at 20V through its single-pole normally-open output. On-resistance for AC is 100mΩ. The company claims it is the smallest relay with this rating. Off-state leakage is 10nA (16V DC).