Surface mount resistors take on new tasks

Welwyn Components is finding specialist new applications for its ranges of standard and custom surface mount resistors.

Welwyn Components is finding specialist new applications for its ranges of standard and custom surface mount resistors offering superior power handling capability for their size, good pulse withstanding performance and excellent accuracy and stability.

One such area is the design of DC/DC convertors, where the drive for enhanced efficiency and reliability is placing increasingly stringent demands on all the constituent components, including the resistor.

Whilst the trend towards reducing component size continues, today's electronic circuits still require reliable protection to operate amidst the potential hazards of inrush currents and high voltage surges.

Often, designers can no longer simply resort to a larger resistor body size to cope with these demands.

The Welwyn solution is the thick film PWC Series (pulse withstanding chip), which combines excellent power handling capabilities with good pulse withstanding performance.

Available in four standard sizes from 0805 to 2512, it offers a resistance range from 1ohm to 10Mohm, tolerance to 0.5% and typical TCR of 100ppm/C.

Its special design permits an enhanced power rating (1.5W at 70C for 2512) and higher limiting element voltage (500V for 2512).

Single pulse, continuous pulse and lightning surge characteristics are significantly better than for ordinary chip resistors.

The stability and accuracy of voltage regulation is important in many DC/DC convertor designs.

Welwyn's thick film PCR Series (precision chip resistor) offers a rugged, lower cost alternative to thin film chip resistors in such applications.

With excellent load stability (0.05% typical), the PCR series offers any resistance value within a specified range of 10ohm to 1Mohm, at a tolerance of 0.1% and TCR of 50ppm/C.

It is available in sizes 0805 to 1206, with power ratings from 0.1 to 0.25W at 70C.

To help electronics systems designers achieve current sensing in high current circuits, Welwyn has developed an ultra-low resistance surface mount resistor capable of handling a power dissipation up to 3W.

The LRF3W Series (low resistance flip-chip 3W), which is the industry's smallest 3W current sense resistor, comes in an inverse form 1225 chip and uses patented, non-noble copper-based thick film materials.

Rated for a full 3W at 70C, the LRF3W is designed to achieve ultra-low resistance values of 0.003 to 0.100ohm with tolerance to 1% and with TCR to 100ppm/C.

They are rated for operation from -55 to +150C.

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