Switch circuit having excess-current detection function
First Claim
1. A switch circuit having an excess-current detection function, comprising:
- a semiconductor switching device disposed between a load and a power source and arranged to turn on or off the connection between said load and said power source in accordance with a control signal supplied to a control terminal thereof;
switch control means arranged to receive an instruction signal output from an instruction-signal output portion and to output the control signal to said control terminal of said semiconductor switching device so as to control supply of electric power from said power source to said load;
electric-current detection means for detecting a load electric current which flows in said load;
excess-current control means for changing on/off control of said semiconductor switching device when detection of said load electric current satisfies at least one of a plurality of an excess current determining conditions previously determined in accordance with the electric characteristics of an electric line between said load and said power source, or electric characteristics of said load; and
an A/D converter connected with said electric-current detection means for converting the detected load electric current from an analog value to a digital value,wherein said excess-current control means has comparison means for subjecting said digital value of said detected load electric current and a reference electric current determined previously in accordance with the electric characteristics to a comparison, to determine an excess current, said excess current being a load electric current that is greater than said reference electric current and count means for counting energizing time in which said excess current flows in said load, and said excess current determining condition is determined by using said excess current and said energizing time; and
wherein said excess-current control means is arranged to determine the excess current when a condition is satisfied such that a predetermined electric current larger than said reference electric current flows in said load for time determined previously in accordance with said electric characteristics and provided with said plurality of excess current determining conditions obtained by combining different set electric currents and set time periods arranged in such a manner that the set time is shortened in inverse proportion to the set electric current, said comparison means further subjects said digital value of said detected load electric current and each of said set electric currents to a comparison, and said count means further counts energizing time in which an electric current larger than each of said set electric currents flow in said load.
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Accused Products
Abstract
A microcomputer 4 responds to an instruction signal to turn the load L on or off to control the FET 2 through the drive circuit 5. The microcomputer 4 samples an electric current IL which is supplied through the A/D converter 6 and which flows in the load L at every predetermined sampling time TS and subjects the sampled electric current IL to a comparison with a known rated current value IR for the load L. When IL ≧IR is satisfied, the microcomputer 4 starts counting energizing time T. When the accumulated value of IL ×TS is enlarged to a predetermined value SO, the microcomputer 4 turns the FET 2 off. When the detected electric current IL is larger than an upper limit IO (>IR) determined previously, the microcomputer 4 immediately turns the FET 2 off through the drive circuit 5.
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Citations
6 Claims
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1. A switch circuit having an excess-current detection function, comprising:
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a semiconductor switching device disposed between a load and a power source and arranged to turn on or off the connection between said load and said power source in accordance with a control signal supplied to a control terminal thereof; switch control means arranged to receive an instruction signal output from an instruction-signal output portion and to output the control signal to said control terminal of said semiconductor switching device so as to control supply of electric power from said power source to said load; electric-current detection means for detecting a load electric current which flows in said load; excess-current control means for changing on/off control of said semiconductor switching device when detection of said load electric current satisfies at least one of a plurality of an excess current determining conditions previously determined in accordance with the electric characteristics of an electric line between said load and said power source, or electric characteristics of said load; and an A/D converter connected with said electric-current detection means for converting the detected load electric current from an analog value to a digital value, wherein said excess-current control means has comparison means for subjecting said digital value of said detected load electric current and a reference electric current determined previously in accordance with the electric characteristics to a comparison, to determine an excess current, said excess current being a load electric current that is greater than said reference electric current and count means for counting energizing time in which said excess current flows in said load, and said excess current determining condition is determined by using said excess current and said energizing time; and wherein said excess-current control means is arranged to determine the excess current when a condition is satisfied such that a predetermined electric current larger than said reference electric current flows in said load for time determined previously in accordance with said electric characteristics and provided with said plurality of excess current determining conditions obtained by combining different set electric currents and set time periods arranged in such a manner that the set time is shortened in inverse proportion to the set electric current, said comparison means further subjects said digital value of said detected load electric current and each of said set electric currents to a comparison, and said count means further counts energizing time in which an electric current larger than each of said set electric currents flow in said load. - View Dependent Claims (2, 3, 4, 5)
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6. A switch circuit having an excess-current detection function, comprising:
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a semiconductor switching device disposed between a load and a power source and arranged to turn on or off the connection between said load and said power source in accordance with a control signal supplied to a control terminal thereof; switch control means arranged to receive an instruction signal output from an instruction-signal output portion and to output the control signal to said control terminal of said semiconductor switching device so as to control supply of electric power from said power source to said load; electric-current detection means for detecting a load electric current which flows in said load; excess-current control means for changing on/off control of said semiconductor switching device when detection of said load electric current satisfies an excess current determining condition previously determined in accordance with the electric characteristics of an electric line between said load and said power source, or electric characteristics of said load; and an A/D converter which converts the detected load electric current from an analog value to a digital value so as to supply said digital value to said excess-current control means, wherein said excess-current control means turns said semiconductor switching device off when said excess current determining condition is satisfied, wherein said excess-current control means includes storage means for storing a reference electric current determined previously in accordance with the electric characteristics, and comparison means for subjecting said digital value of said detected load electric current and said reference electric current to a comparison to determine an excess current when said digital value of said detected load electric current is larger than said reference electric current, and wherein said storage means further stores a high-level reference electric current higher than said reference electric current and a predetermined set time, and said excess-current control means is further provided with count means for counting a lapse of time from time at which said semiconductor switching device has been switched on by said switch control means to determine an excess current when said digital value of said detected load electric current is larger than said high-level reference electric current in a state where said lapse of time is shorter than said set time and to determine an excess current when said digital value of said detected load electric current is larger than said reference electric current in a state where said lapse of time is longer than said set time.
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Specification