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
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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.
Claims15
A protection circuit, comprising:
- a bi-metallic strip having an input side and an output side to couple along an input path to a load;
- a depletion mode field effect transistor (D MOSFET) connected in series with and thermally tied to the bi-metallic strip, the D MOSFET having a source terminal, coupled to a ground path;
- and an internal control circuit, wherein the internal control circuit is connected between the input path and ground path and is coupled to a gate terminal of the D MOSFET, the internal control circuit comprising:
- a transient voltage suppression (TVS) diode, coupled between the input path and the ground path;
- a switching MOSFET, having a drain terminal coupled to the gate terminal of the D MOSFET;
- and an Op amp comparator, coupled to a drain terminal of the D MOSFET.
A method of controlling an electrical current through a load line, comprising:
- passing the electrical current through a bimetallic switch formed of a bimetallic strip to a depletion mode transistor of a protection circuit that is coupled to the load line;
- determining a current value of the electrical current, after passing through the bimetallic strip;
- and
- outputting a high signal to a switching transistor when an overcurrent condition occurs, wherein the current value reaches a preset level, wherein the switching transistor generates a short circuit across the depletion mode transistor, and wherein the depletion mode transistor enters a low bias saturation that limits a level of the electrical current;
- wherein the depletion mode transistor comprises a first field effect transistor, wherein the short circuit is generated between a gate and a source of the depletion mode transistor.
Dependencies are inferred from the claim text.