TT electronics / Welwyn Components has introduced a new series of UL1412 recognized fusible resistors that uses an advanced coating and production process to ensure safe, silent operation in overload conditions. This allows designers to more easily meet the requirements of UL approval, while eliminating the need to put additional fuses in series with the input resistor. The ULW series wirewound resistors overcome the problems associated with conventional flameproof resistors as well. The resistor coating meets UL94-V0 standards so it will not burn or emit incandescent particles under any condition of applied temperature or power overload.
These UL-recognized resistors are available in standard values from 4.7 to 100O. Four types are offered: ULW2 is rated 2W and provides a 5s overload of 10W along with 250V isolation; 3W-rated ULW3 ensures a 15W overload with 350V isolation; the ULW4 model protects overloads up to 20W with 500V isolation and a 4W nominal rating and the ULW5 model protects overloads up to 25W with 500V isolation.
ULW is targeted at mains input protection for small power supplier and battery chargers. Designed for inrush limiting in those PSU circuits where greater pulse performance is required. It controls the inrush of current at switch-on, protects the circuit against mains borne transients and protects against fire by breaking the circuit under fault conditions.