High Speed Fuses

In relation to size thyristors, transistors and IGBTs are handling large amounts of power. Therefore, they are often used in applications such as soft starters, inverters, frequency converters, voltage converters, battery systems and static relays. The compact size of semiconductors means that they must be protected from overheating and too high current density in the PN transitions.

Fuses consist of a conductor with good conductivity that has been divided into a number of overload points that melt and break the circuit in case of too high current. Around the overload points there is typically a powdered quartz material that extinguishes the spark as the conductor melts. The fuse package is usually made of ceramic or plastic material.

High speed fuses are specially designed to protect semiconductors and are sometimes called I2T fuses. In high speed fuses, the overload points break extremely fast to minimize the current heat pulse, I2T (transmitted energy). High speed fuses also have improved thermal conductivity to dissipate excess heat. When choosing the right fuse for semiconductor protection the rated voltage of the fuse must be equal to or higher than the nominal voltage of the circuit. The I2T of the fuse must be less than or equal to I2T according to the semiconductor data sheet. Nominal current in the circuit must also be considered when choosing the fuse.

The Littelfuse PSR squary body family of fuses includes fuses for 690/700 V AC and 1250/1300 V AC. The PSR fuses are also marked with their rating of direct voltage from 500 to 1000 V. Rated currents range from 40 A to 2000 A.

Comptronic AB       Phone: 08-564 706 70       E-mail: mailbox@comptronic.se       Address: Stormbyvägen 2-4, 163 55 Spånga       Mon-Fri: 08.30–17.00