US3569781A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Motor protection circuit
Assignee: Texas Instruments Inc
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Filing: 1968-12-30
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Granted: 1971-03-09
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Expires: 1988-12-30
Abstract
Abstract Apparatus controls the energization of an electrical load and is responsive to overheating of the load for protective deenergization thereof. The apparatus includes a gate triggerable semiconductor current switching device interconnected with means for energizing the electrical power load in response to conduction between the main terminals of the device. A thermistor thermally coupled to the load is interconnected with the gate terminal of the device for controlling the flow of triggering current thereto. Means is provided which is interconnected with the thermistor for initially supplying triggering current to initiate conduction between the main terminals of the device and then to supply a triggering current to latch the device in a conductive state. The thermistor reduces the triggering current to the device thereby to deenergize the load if heated above a predetermined threshold by overheating of the load.
Inventors
- 👤 Richard W Strachan
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-25 13:02
CPC Classifications
H; H02; H02H; H02H5/00; H02H5/04; H02H5/042
Claims Analysis
Total Claims: 17
Claim 1
Independent Claim
246 words
Apparatus for controlling the energization of an electrical load and which is responsive to overheating of the load for protective deenergization thereof, comprising: a triggerable AC semiconductor current switching device having main and gate terminals, AC conduction between the main terminals being initiated by applying a triggering current to the gate terminal and being terminated when the triggering current is reduced below a predetermined triggering level; means, interconnected with the AC current switching device for connection across an AC power source, for energizing the load in response to conduction between the main terminals of the current switching device; a thermistor thermalLy coupled to the load and interconnected with the gate terminal of the current-switching device for controlling the flow of triggering current thereto; and means interconnected with the thermistor and with said gate terminal for supplying a triggering current for the AC currentswitching device, said means being operative initially to supply triggering current to said gate terminal for initiating conduction between the main terminals of the AC switching device upon connection of the apparatus across the AC power source and then to supply triggering current to said gate terminal through said thermistor for latching the AC switching device in a state wherein conduction between the main terminals thereof is recurrently maintained, the thermistor reducing the triggering current below said predetermined triggering level when heated above a predetermined threshold corresponding to a maximum permissible temperature in the load whereby the load is protectively deenergized upon overheating thereof.
Claim 2
Dependent Claim
246 words
Apparatus for controlling the energization of an electrical load and which is responsive to overheating of the load for protective deenergization thereof, comprising: a triggerable AC semiconductor current switching device having main and gate terminals, AC conduction between the main terminals being initiated by applying a triggering current to the gate terminal and being terminated when the triggering current is reduced below a predetermined triggering level; means, interconnected with the AC current switching device for connection across an AC power source, for energizing the load in response to conduction between the main terminals of the current switching device; a thermistor thermalLy coupled to the load and interconnected with the gate terminal of the current-switching device for controlling the flow of triggering current thereto; and means interconnected with the thermistor and with said gate terminal for supplying a triggering current for the AC currentswitching device, said means being operative initially to supply triggering current to said gate terminal for initiating conduction between the main terminals of the AC switching device upon connection of the apparatus across the AC power source and then to supply triggering current to said gate terminal through said thermistor for latching the AC switching device in a state wherein conduction between the main terminals thereof is recurrently maintained, the thermistor reducing the triggering current below said predetermined triggering level when heated above a predetermined threshold corresponding to a maximum permissible temperature in the load whereby the load is protectively deenergized upon overheating thereof.
Claim 3
Dependent Claim
27 words
Control apparatus as set forth in claim 1 wherein said thermistor is a PTC thermistor having a transition temperature above which the resistance thereof rises relatively abruptly.
Claim 4
Dependent Claim
54 words
Control apparatus as set forth in claim 1 wherein said means for supplying a triggering current for the current switching device includes means for resetting the apparatus after the load has been protectively deenergized and has cooled whereby the load can only be reenergized at a temperature thereof less than said maximum permissible temperature.
Claim 5
Dependent Claim
53 words
Control apparatus as set forth in claim 3 wherein said means for resetting the apparatus includes a resistance connected with said thermistor between one of the main terminals and the gate terminal of the switching device, said resistance supplying the triggering current for initiating conduction between the main terminals of the current-switching device.
Claim 6
Dependent Claim
21 words
Control apparatus as set forth in claim 4 wherein said resistance comprises a second thermistor, said thermistor being a PTC thermistor.
Claim 7
Dependent Claim
77 words
Control apparatus as set forth in claim 5 wherein said second thermistor is self-heating upon connection of the apparatus to the AC power source whereby, after the load is protectively deenergized, said second thermistor supplies insufficient triggering current for initiating conduction between the main terminals of the switching device until the apparatus is disconnected from the AC power source to permit cooling of said second thermistor whereby said second thermistor provides means for manually resetting the apparatus.
Claim 8
Dependent Claim
51 words
Control apparatus as set forth in claim 5 wherein said second thermistor is also thermally coupled to the load and has a transition temperature above which the resistance thereof rises relatively abruptly, whereby said second thermistor provides means for automatically resetting the apparatus at a predetermined reset temperature of the load.
Claim 9
Dependent Claim
46 words
Control apparatus as set forth in claim 3 further comprising time delay means responsive to termination of conduction between the main terminals of the current-switching device upon overheating of the load for providing a predetermined delay between protective deenergization of the load and subsequent reenergization thereof.
Claim 10
Dependent Claim
99 words
Control apparatus as set forth in claim 8 wherein said time delay means includes an NTC thermistor having a transition temperature above which the resistance thereof decreases relatively abruptly, said NTC thermistor being connected with the first-said thermistor between one of the main terminals and the gate terminal of the switching device, and a heater for said NTC thermistor, the heater being connected across said main terminals whereby, when conduction between said main terminals is terminated, the heater heats said NTC thermistor, which, after said predetermined delay to reach said transition temperature, supplies current for retriggering the switching device.
Claim 11
Dependent Claim
27 words
Control apparatus as set forth in claim 9 wherein saiD heater is a PTC thermistor having a transition temperature above which the resistance thereof increases relatively abruptly.
Claim 12
Dependent Claim
24 words
Control apparatus as set forth in claim 5 wherein said second thermistor has a transition temperature above which the resistance thereof increases relatively abruptly.
Claim 13
Dependent Claim
50 words
Control apparatus as set forth in claim 5 wherein said second thermistor is thermally coupled to the switching device whereby the triggering current supplied to the switching device by said second thermistor for initiating conduction between said main terminals varies as a function of the temperature of the switching device.
Claim 14
Dependent Claim
38 words
Control apparatus as set forth in claim 12 wherein said second thermistor is connected in series with a resistance, and said thermistor and resistance are connected in parallel with a second resistance to constitute a temperature compensation network.
Claim 15
Dependent Claim
46 words
Control apparatus as set forth in claim 1 wherein said means for supplying a triggering current for the current-switching device includes a resistance and a capacitor connectable between one side of the AC power source to the gate terminal of the switching device through said thermistor.
Claim 16
Dependent Claim
49 words
Control apparatus as set forth in claim 1 further comprising a resistance and a capacitor connected in series across the main terminals of the current-switching device, and a capacitor connected between the gate terminal and one of the main terminals of the device for providing immunity from transient triggering.
Claim 17
Dependent Claim
15 words
Control apparatus as set forth in claim 1 wherein said current-switching device is a triac.
References Cited (Backward Citations)
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1974-03-08 | 1974-09-07 | 1975-03-09 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1978-03-08 | 1978-09-07 | 1979-03-09 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1982-03-08 | 1982-09-07 | 1983-03-09 | $7700.00 | Window Closed / Lapsed |