LA50 VERY FAST-ACT SEMICOND FUSE QS150-4. In response to new equipment requirements, Littelfuse LA50QS series fuses were developed to improve the overall performance of semiconductor fuses. The LA50QS provides the best protection features including lower I2t, longer life when subjected to cyclic loading and lower watts loss. LA50QS is today.s choice for the protection of dynamic solid state equipment. Features: Lowest I2t for greatest protection of semiconductor circuits. Low watts loss for cooler operation. Superior cycling ability gives an equipment design advantage. State-of-the-art protection for 500 volt equipment. Ultra compact sizes allow down-sizing of existing equipment. Applications: Protection of 500 volts or less solid state equipment such as motor drives, UPS, inverters, etc.