Electronic Design

Circuit Protection Devices

Telecom Overvoltage Protectors Target Through-Hole Applications
Bourns Inc.
(909) 781-5500; fax (909) 781-5006; www.bourns.com

The TISP4xxxLM series of telecom overvoltage protectors features modified TO-92 packaging. The devices are suited for cost-sensitive, through-hole applications. The high-performance chip is available in 100-, 50-, and 35-A 10/1000 versions. Each current rating is available in up to 17 different protection voltages between 70 and 400 V.

Low-capacitance guarantees are provided under various bias conditions. Also, surge performance is guaranteed against an extensive list of international standards. Members of this series provide symmetrical, bidirectional protection in a two-lead variant of the TO-92 package. Comprehensive datasheets list performance against surge standards such as FCC Part 68 and ITU-T K20, K21. Low capacitance values, high holding current, and low off-state current combine to guarantee dynamic performance. The devices may be used individually for two-wire devices, such as telephones or modems. They may be used in combination for multipoint protection. Matching performance is also available in a DO-214 AA (SMB) packaged device, providing an easy migration path for designs expected to move to surface-mount assembly.

The devices are now available in either bulk or tape-and-reel packaging. Optionally, formed leads may be ordered in tape-and-reel form. In 2000-unit quantities, pricing ranges from $0.35 to $0.45.



Low-Cost Meshes And Screens Suit OEM Requirements
Tecan Components
(877) 99-TECAN; fax (877) 990-4700; www.tecan-inc.com

A comprehensive range of precision metal components includes meshes, sieves, screens, nets, and filters. Designed as an economical alternative to machined metal or cover screens, these devices suit virtually any OEM requirement.

The metal components are formed by photo-chemical machining and photo-electroforming. This process enables the company to create products of varying complexity. Products include mesh or screens produced as flat sheets, flexible products, or in three-dimensional forms.

Single-sheet screens do not have crossover areas. This configuration eliminates contamination due to trapped debris. Also, single-sheet screens offer consistent cross-sectional thickness and more accurate aperture sizes. There is no possibility of delamination of the edges. The durable screens are available with various surface textures, such as bright, semi-bright, matte, smooth, or brushed. The manufacturing processes are so precise that mesh grids are available as small as 6 µm. No subsequent machining or polishing is required. For pricing and availability information, contact the company.



Thermally Protected Metal Oxide Varistor Offers Fast Response Time
Littelfuse Inc.
(800) 999-9445; fax (847) 391-0459; www.littelfuse.com

The TMOV varistor is a dual-functioning metal oxide varistor. It offers the same functionality as the company's UltraMOV series radial-leaded metal oxide varistors. It also incorporates the added safety of a thermally activated element to prevent thermal runaway due to sustained abnormal overvoltage conditions.

Unlike other typical component combinations, the thermally activated element is integrated into the body of the TMOV. This configuration results in a faster response time for improved safety and performance. The use of a single TMOV device in place of product combinations offers cost and procurement benefits. Vital board-space savings helps to reduce end-product size. This device is UL approved to protect against thermal runaway arising from sustained abnormal overvoltage conditions for both cord-connected and permanently connected transient voltage surge suppression (TVSS) devices. Available operating voltages range from 130 to 320 V in both 14- and 20-mm packages. The device is suited for use in power meter, uninterruptible power source (UPS), and ac panel protection products. In 50,000-unit quantities, the 14-mm TMOV starts at $0.30. The 20-mm package starts at $0.46 in similar quantities.



Radial-Leaded Microfuse UL Rated At 277 V AC
Bel Fuse Inc.
(800) BEL-FUSE; fax (201) 432-9542; www.belfuse.com

The Type MRT time-lag, radial-leaded microfuse is suited for use in wall-mount power supplies used in cellular-phone chargers. The device is now UL rated at 277 V ac (80 mA to 6.3 A) with an interrupting (short-circuit) rating of 100 A. These ratings make the microfuse ideal for use in specific domestic lighting ballasts. The device is CSA certified, VDE/SEMKO approved to IEC 127-3/SS4, and carries the safety approval of MITI. Designers can specify a single part number to satisfy the requirements of U.S., Asian, and European markets.

The microfuse suits a wide range of board-level, secondary-circuit (primary circuits to 277-V ac maximum) protection applications, including computer boards and audio/video circuits. The device measures just 8.5 by 7.7 mm. It is provided in long (18.8 mm) or short (4.3 mm) radial-leaded versions for maximum space savings and design flexibility. The MRT series fuses may be ordered in bulk (short-lead version) or on tape in ammo packs. In 5000-unit quantities, pricing for the devices starts at $0.14 each.



Time-Delay And Fast-Acting Fuses Meet UL/CSA Or IEC Standards
Cooper Electronic Technologies
(561) 752-5000; fax (561) 742-0134; www.cooperET.com

The 1025 series of brick fuses includes the 1025TD and 1025FA time-delay and fast-acting fuses. The devices are designed to North American standards with UL and CSA agency listings. The 1025T and 1025F are time-delay and fast-acting fuses designed to European IEC standards with SEMKO and VDE approval. The time-delay fuses feature 250-mA to 5-A full-load currents. The full-load currents of the fast-acting fuses range from 250 mA to 15 A.

The devices can replace glass-tube fuses for off-line overcurrent protection. According to the company, the 1025 series is the first complete series of 250-V rated surface-mount products to comply with the EIA/IS-722 environmental standards. For pricing and availability information, contact the company.



Power MOSFETs Boast ESD Protection To 2000 V
Vishay Siliconix
(610) 644-1300; fax (610) 296-0657; www.vishay.com

The Little Foot SC-70 power MOSFETs feature the lowest level of thermal resistance achieved for this package type. Thermal resistance is 35°C/W for single-channel devices and 80°C/W for dual-channel devices. This lower thermal resistance increases power dissipation to a maximum of 1 W in the single-channel SC-70 package. It also allows the device to run cooler. Low thermal resistance contributes to the reduced conduction losses provided by these devices. Compared to standard SC-70 equivalents, the Little Foot SC-70 devices feature RDS(ON) ratings that are 25% lower. These ratings extend lithium-ion battery power.

The Little Foot devices measure just 2 by 2.1 mm with a 1-mm height profile. They are targeted to small- to medium-load switching, power-amplifier switching, and level-shifting applications in cell phones, pagers, PDAs, and other handheld devices. ESD protection prevents malfunction when the MOSFETs are used in portable systems with attachable/detachable accessories, including SIM cards, Bluetooth adapters, IrDA adapters, MP3 adapters, and cable connections to other portable equipment. Versions include single, dual, and complementary n-channel and p-channel devices with breakdown voltages of 12, 20, and 25 V. On-resistance at a ±4.5-V gate drive ranges from 70 mΩ for the single n-channel Si1410EDH to 490 mΩ for the dual p-channel Si1913EDH. All eight devices are rated for operation at 1.8, 2.5, and 4.5 V.

In 100,000-unit quantities, pricing for the Little Foot SC-70 devices ranges from $0.35 to $0.39.



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