Review

Circuit breakers, fuses and transient voltage suppressors have been protecting electronic equipment from short circuits, voltage spikes and the like for decades. But like most other electronic products, circuit protection devices must change and evolve to keep pace with the latest developments in electronics.

Circuit breakers coming to market this year were designed to serve industrial applications, especially those employing DIN rails or terminal blocks. For example, the 1180 series from E-T-A Circuit Breakers (e-t-a.com) were developed to replace the fuses commonly used in DIN-rail terminal blocks for protecting factory control equipment. Only 8 mm wide, the compact circuit breakers can be used in any terminal block system that accepts fuses having a SAE J1284 footprint. The devices work with voltages up to 250 Vac or 65 Vdc and current ranging from 0.1A to 10A.

Another example is the TCP thermal miniature circuit breaker from Phoenix Contact (phoenixcon.com). Designed for use with terminal blocks, the circuit breakers offer an integrated switching function that allows tripped circuits to be immediately switched back on; the breaker also doubles as an on/off switch. The modular base terminal block and pluggable circuit breaker make it possible to implement a multitude of power distribution tasks, ranging from 0.25A-10A at either 250 Vac or 65 Vdc.

For power handling capability, the 483 Series from E-T-A Circuit Breakers was claimed as the first MS 3320-type circuit breaker to be rated to 35A. Among its many features is an advanced dual chamber construction, allowing the breakers to handle large DC currents.

For fuses, much of the innovation this year was in the development of SMT and lead-free variations of these devices. An example of a fuse that had both features was the OMT 125 series from Schurter (schurter.com). Spanning current rating from 500 mA to 5A at 125V, the fuses are surface-mount and lead-free, including the fusing element. They feature time-lag operation and can handle fault currents of up to 100A at 125 Vac/Vdc.

Innovation in the transient voltage suppressor (TVS) arena came from products like the ET723 from Protek Devices (protek.com). It offers protection from transients for FireWire, USB1.1/2.0, 10/100/1000 BaseT Ethernet, and other high-speed interfaces. The ET723 is a 6-line steering diode array with a capacitance of less than 5 pF. The TVS array is said to have little effect on signal integrity while protecting the circuitry from transients. The device is able to protect up to six I/O lines by clamping the transient voltage to the power source lines or ground. Designed to meet IEC 61000-4-2 (ESD), 61000-4-4 (EFT) and 61000-4-5 (lightning surge) transient specs, the diodes can be connected in parallel for increased transient current protection.

Another interesting product in the TVS area is the AK series from Littelfuse (littelfuse.com). It is capable of eliminating the ganging of between 40 and 150 5-kW silicon avalanche diodes, eliminating errors and lowering costs. The AK10 can handle currents of up to 10 kA via an 8/20-µs wave-shape pulse as per IEC 61000.4.5 in a 16.5-mm leaded package. The AK6 can handle up to 16 kA. Both TVSs employ proprietary Foldbak technology, which serves to lower clamping levels below the diode's avalanche state. The devices also feature a capacitance of 2 nF at 10 kHz, clamping voltage as low as 58V, and bi-directional protection with bleed-through leakage levels down to 20 µA.

—Joe Desposito

Outlook

Follow The Leaders
Applications for circuit protection devices cover a large swath of the electronics industry, from power supplies to communications devices to industrial electronics and so on. And as electronic products in all of these areas evolve, so must circuit protection, though the latter is a follower rather than a leader. In other words, the need for protection precedes the protection device. So for 2004 we expect incremental changes in these devices, such as more power handling capability and the like, as well as breakthrough changes in these devices that will be designed to serve new electronics technologies.

—JD