Overcurrent protection by depletion mode MOSFET or JFET and bi-metallic temperature sensing switch in mini circuit breaker
AssigneeLittelfuse, Inc.
InventorsChuan Fang Chin, Teddy To
Life of this patent
Estimating the term…
Abstract
A miniature circuit breaker for providing short circuit and overload protection is disclosed herein. The miniature circuit breaker features a field effect transistor (FET), which may be a depletion mode metal oxide semiconductor FET (D MOSFET), a junction field-effect transistor (JFET), or a silicon carbide JFET, the FET being connected to a bi-metallic switch, where the bi-metallic switch acts as a temperature sensing circuit breaker. In combination, the D MOSFET and bi-metallic switch are able to limit current to downstream circuit components, thus protecting the components from damage.
Claims18
A miniature circuit breaker, comprising:
- a switch to be manually opened or closed by an external lever;
- a magnetic coil comprising a moving valve, the moving valve to connect with the switch in response to a first fault event, opening the switch;
- a bi-metallic strip to connect with the switch in response to a second fault event;
- and
- a field effect transistor (FET) connected in series with and thermally tied to the bi-metallic strip, the FET having a gate terminal and a source terminal, wherein the gate terminal is connected to the source terminal, wherein the bi-metallic strip and the FET open the switch during the second fault event;
- wherein the bi-metallic strip comprises a first metal comprising a first coefficient of thermal expansion and a second metal comprising a second coefficient of thermal expansion, wherein the first coefficient of thermal expansion is different from the second coefficient of thermal expansion;
- and
- wherein the first metal comprises a winding, wherein the winding is removed before the FET is thermally tied to the bi-metallic strip.
A miniature circuit breaker, comprising:
- a bi-metallic strip comprising an elongated metal strip and a metal winding wrapped around the elongated metal strip, wherein the elongated metal strip bends in response to a current rating of the miniature circuit breaker being exceeded;
- a field effect transistor (FET) connected in series with and thermally tied to the elongated metal strip after the metal winding is removed from the bi-metallic strip, the FET having a gate terminal connected to a source terminal;
- and
- a switch to open in response to an incoming current that exceeds the current rating, wherein the switch opens in response to the bending of the elongated metal strip;
- wherein current limiting above the current rating is provided by the FET;
- wherein the elongated metal strip is formed of a first metal having a first coefficient of thermal expansion and the metal winding is formed of a second metal having a second coefficient of thermal expansion, wherein the first coefficient of thermal expansion is different from the second coefficient of thermal expansion;
- and
- wherein the metal winding is removed before the FET is thermally tied to the bi-metallic strip.
Dependencies are inferred from the claim text.