Switch circuit having excess-current detection function

• US 6,011,416 A
• Filed: 11/19/1997
• Issued: 01/04/2000
• Est. Priority Date: 02/19/1997
• Status: Expired due to Term

• Current Assignee: Autonetworks Technologies, Ltd. (Sumitomo Corporation)
• Original Assignee: Harness System Technologies Research, Ltd. (Sumitomo Corporation), Sumitomo Electric Industries Limited (Sumitomo Corporation), Sumitomo Wiring Systems Limited (Sumitomo Corporation)
• Inventors: Hoshino, Takashi, Mizuno, Fumiaki, Miyazaki, Yoshiyuki, Kido, Motonori
• Primary Examiner(s): Callahan, Timothy P.
• Assistant Examiner(s): Englund, Terry L.
• Application Number:
  US08/974,604
• Time in Patent Office: 776 Days
• Field of Search: 361/93, 361/94, 361/95, 361/96, 361/97, 361/98, 361/100, 361/101, 361/18, 361/54, 361/57, 327/108, 327/109, 327/110, 327/198, 327/321, 327/434, 327/77, 323/277, 307/116, 307/130, 307/131
• US Class Current: 327/108
• CPC Class Codes: H02H 1/043 to inrush currents H02H1/046 takes precedence; differential protection of transformers H02H7/045
• CPC Class Codes: H02H 3/085 making use of a thermal sensor, e.g. thermistor, heated by the excess current also responsive to the temperature of the protected device H02H5/041, thermal images H02H6/00
• CPC Class Codes: H02H 3/087 for dc applications
• CPC Class Codes: H02H 3/0935 the timing being determined by numerical means
• CPC Class Codes: H03K 17/0822 in field-effect transistor switches
• CPC Class Codes: H03K 17/18 Modifications for indicating state of switch

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 I_L which is supplied through the A/D converter 6 and which flows in the load L at every predetermined sampling time T_S and subjects the sampled electric current I_L to a comparison with a known rated current value I_R for the load L. When I_L ≧I_R is satisfied, the microcomputer 4 starts counting energizing time T. When the accumulated value of I_L ×T_S is enlarged to a predetermined value S_O, the microcomputer 4 turns the FET 2 off. When the detected electric current I_L is larger than an upper limit I_O (>I_R) determined previously, the microcomputer 4 immediately turns the FET 2 off through the drive circuit 5.

Claims

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.

2. A switch circuit having an excess-current detection function according to claim 1, wherein said semiconductor switching device, said switch control means and said excess-current control means are integrally formed on a substrate.

3. A switch circuit having an excess-current detection function according to claim 2, wherein said electric-current detection means is furthermore integrally formed on said substrate.

4. A switch circuit having an excess-current detection function according to claim 1, wherein a storage means included in the excess-current control means 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 then 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.

5. A switch circuit having an excess-current detection function according to claim 4, wherein said storage means further stores a low-level reference electric current smaller than said reference electric current and said excess-current control means further determines abnormality when said digital value of detected load electric current is smaller than said low-level reference electric current in a state where said lapse of time is longer than said set time.

6. 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 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.