Electricity: electrical systems and devices – Safety and protection of systems and devices – Circuit interruption by thermal sensing
Reexamination Certificate
2000-03-29
2001-08-07
Leja, Ronald W. (Department: 2836)
Electricity: electrical systems and devices
Safety and protection of systems and devices
Circuit interruption by thermal sensing
C439S830000, C439S870000
Reexamination Certificate
active
06272000
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates generally to blade-type fuses and, more particularly, to blade-type fuses for being secured to circuit boards.
Fuses are widely used as overcurrent protection devices to prevent costly damage to electrical circuits. One type of fuse for personal computer power supplies is a blade-type fuse. The blade-type fuse includes a plastic housing, two electrical conducting terminal blades extending from the housing, and a fusible link connected between the terminal blades within the housing. The terminal blades are inserted through openings in a printed circuit board and soldered to the board to complete an electrical connection through the fusible link. In operation, when the current approaches unacceptable limits, the link melts and opens the circuit to prevent electrical component damage.
Fuses and other components are typically secured to a circuit board by soldering. Wave soldering is one known soldering technique that is simple and reliable. With wave soldering, the electrical components are stuffed onto a printed circuit board, a solder flux is applied to the board, the board is preheated, and the board is transported across one or several solder waves.
Proper location of a fuse on the circuit board is important to provide a desired electrical connection. For example, if the fuse housing contacts the board when terminal blades are inserted through the board, solder wicking and the creation of an electric path around the fuse may result. Also, a portion of the blade terminal that extends, or protrudes, from a bottom of the board typically must be trimmed after soldering to prevent undesired electrical contacts between the terminals and other components.
Accordingly, it would be desirable to provide a blade-type fuse that facilitates the proper location of a fuse with respect to a circuit board to prevent the fuse housing from resting on a surface of the board and that eliminates a need to trim the terminals after soldering.
BRIEF SUMMARY OF THE INVENTION
In an exemplary embodiment of the invention, terminal blades extending from a housing of a fuse include stop portions and hold portions to facilitate properly locating a fuse with respect to a circuit board. Particularly, and in the exemplary embodiment, the blades have opposite flat faces and include stop portions configured to prevent the blades from being inserted through a printed circuit board for more than a predetermined distance. The hold portions are configured to hold the fuse housing in a separated position from the surface of the board during soldering.
More particularly, and in the exemplary embodiment, the stop portion of each blade includes a projection configured to extend from at least one of the flat faces of the blades. The stop portion is dimensioned so that the blade and projection together have a cross-sectional area greater than the area of the blade terminal opening in a circuit board so that the blade cannot be inserted through the circuit board opening beyond the stop portion. By locating the stop portion a selected distance from the bottom of the blade housing along a longitudinal axis of the blade, the stop portion prevents the blade fuse housing from resting on a surface of the board.
The hold portion also includes a projection configured to extend from at least one flat face of the blades. The hold portion projection is separated from the stop portion projection and has a cross sectional area smaller than the stop portion projection so that the hold portion projection and blade may be inserted through the blade terminal opening in a printed circuit board. The hold portion is positioned at a distal end of the blade, and facilitates maintaining the blade terminals in place during handling and soldering of the boards.
The above-described stop portion prevents the fuse housing from contacting the board surface as the terminal blades are inserted into the circuit board. Therefore, solder wicking and the creation of electrical paths around the fuse are avoided. In addition, the stop and hold portions maintain the fuse in place during handling and soldering operations, thereby preventing the terminals from dislodging from the circuit board during handling and/or soldering. The stop and hold portions also eliminate trimming of the terminal blades, providing further cost savings and reducing manufacturing time.
REFERENCES:
patent: 3786402 (1974-01-01), Horecky
patent: 4343530 (1982-08-01), Leger
patent: 4612539 (1986-09-01), Gurevich et al.
Green Curtis R.
Hunkins John E.
Rupp Terry E.
Spaunhorst Vernon R.
Armstrong Teasdale LLP
Cooper Technologies Company
Leja Ronald W.
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