Surge protection in the line input of a power supply is enhanced by using a line input resistor, and this can often serve a second function as a fuse. Designing a surge resistor which is also a fusible resistor is a challenge. But it is also a core competence of TT Electronics' engineering team.

WHS series wirewound high surge resistors were developed as a result of many years of experience assisting power supply circuit designers who were seeking to limit line input inrush current and achieve lightning strike surge protection. Often this forces the use of excessive power ratings, but WHS offers the solution of high surge energies of up to 250J within relatively compact body sizes. By using wirewound technology with optimised choice of alloy and winding design, and in some cases, multiple parallel windings, WHS can replace composition resistors. And it does so without the lack of stability and of fusibility inherent in composition technology. With a value range 1R0 to 330R and power ratings from 2 to 10W, WHS series offers an immediate solution for many line input designs, but like many of our components it can also be customised.

UL recognised wirewound fusible resistors are recommended for safety critical use in line input circuits where safe fusing is essential in the event of malfunction. Not only is this good practice as a means of protecting against fire, but it also facilitates obtaining and maintaining UL approval on the end product.

WHS series

• High energy surge resistor

• UL94-V0 flameproof protection

• Radial taped form available

• Surface mount ZI-form available

• Non inductive type available

• Enhanced field reliability of line input circuits

• Reduced body size compared to uprated or multiple standard wirewound parts