Electricity: electrical systems and devices – Safety and protection of systems and devices – Circuit interruption by thermal sensing
Reexamination Certificate
2000-10-19
2003-06-24
Jackson, Stephen W. (Department: 2836)
Electricity: electrical systems and devices
Safety and protection of systems and devices
Circuit interruption by thermal sensing
C361S058000, C361S103000
Reexamination Certificate
active
06583977
ABSTRACT:
TECHNICAL FIELD
This invention relates generally to current limiting circuits, and more particularly to current limiting circuits sensing a condition, like electrical current, to clear a fuse.
BACKGROUND
Many electrical circuits currently employ fuses as over-current protection devices. For example, if you accidentally drop a hair dryer into a sink full of water, the water causes a large amount of current to flow. To protect people from shock, a fuse in the hair dryer might clear, thereby “opening” the circuit. When the circuit is open, no current will flow. Likewise, many electronic devices use fuses to protect sensitive electronic components from damage. For example, cellular telephones sometimes use fuses to prevent damage to a sensitive microprocessor.
The problem with fuses in electronic devices is that they are not very accurate. When a fuse is rated at 1 Amp, it will generally clear after a 1 Amp current passes through it for a specified time. As fuses are manufactured en masse, however, there is variability in the manufacturing process. Thus, a 1 A fuse could be 1.1 A, or it might be 0.9 A, etc. Sometimes the tolerances on fuses can run as high as plus or minus twenty percent! If your expensive microprocessor needs 0.9 A to operate, yet can be damaged at 1.1 A, you have a problem in that the fuse you select may allow your processor to be damaged.
There is thus a need for a more accurate current limiting means.
REFERENCES:
patent: 3828289 (1974-08-01), Hickling
patent: 6456186 (2002-09-01), Oglesbee
Burrus, IV Philip H.
Jackson Stephen W.
Motorola Inc.
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