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US 5,805,393 AGranted
Overcurrent protection circuit with improved PTC trip endurance
AssigneeRaychem Corporation
InventorBrian Thomas
Life of this patent
Estimating the term…
Abstract
An overcurrent protection system which will give a rapid response to overcurrents which cause a reduction in the voltage across the load, e.g. a partial or complete short across the load, and which will preserve the trip endurance of a PTC device used in the protection system. The new system maintains the trip endurance of the PTC device by removing the source voltage from the PTC, while still keeping the circuit protection arrangement in a fault state, thereby continuing to protect the load.
Claims7
An electrical system which can be connected between an electrical power supply and an electrical load to form an operating circuit, and which when so connected protects the circuit from overcurrents, which system comprises:
- a. a control element which, in the operating circuit, is connected in parallel with the load;
- and
- b. a circuit interruption element and a bypass element which, in the operating circuit, are coupled in parallel, the parallel combination coupled in series between the electrical power supply and the parallel combination of the electrical load and the control element;
- wherein
- i. the circuit interruption element has
- (1) a closed state which permits the flow of a normal current, I.sub.NORMAL, through the circuit interruption element, and
- (2) an open state which permits the flow of at most a reduced current, substantially less than I.sub.NORMAL, through the circuit interruption element;
- ii. the control element has
- (1) an on state, when the voltage across the control element is a normal voltage, V.sub.NORMAL,
- (2) an off state, when the voltage across the control element falls to a value V.sub.FAULT, or less, and
- is functionally linked to the circuit interruption element so that when the control element is in the on state, the circuit interruption element is in the closed state, and when the control element is in the off state, the circuit interruption element is in the open state;
- and
- iii. the bypass element, comprises a parallel combination of a first bypass path and a second bypass path, and has
- (1) a start-up state such that, if the circuit interruption element is in the open state and a current I.sub.NORMAL is passed through the bypass element, substantially all the current through the bypass element passes through the first bypass path, and the voltage across the control element is greater than V.sub.FAULT, and
- (2) a stopped state such that if the circuit interruption element is in the open state as a result of the voltage across the control element having fallen to a value V.sub.FAULT or less, substantially all the current through the bypass element passes through the second bypass path, and the current through the bypass element is such that the voltage across the control element remains at a value of V.sub.FAULT or less.
12 more elements
An electrical circuit, comprising an electrical power supply, an electrical load, and an electrical protection system which protects the electrical circuit from overcurrents, which system comprises:
- a. a control element which is connected in parallel with the load;
- b. a circuit interruption element and a bypass element which are coupled in parallel, the parallel combination coupled in series between the electrical power supply and the parallel combination of the electrical load and the control element;
- wherein
- i. the circuit interruption element has
- (1) a closed state which permits the flow of a normal current, I.sub.NORMAL, through the circuit interruption element, and
- (2) an open state which permits the flow of at most a reduced current, substantially less than I.sub.NORMAL, through the circuit interruption element;
- ii. the control element has
- (1) (i) an on state, when the voltage across the control element is a normal voltage, V.sub.NORMAL, and
- (ii) is converted to an off state, when the voltage across the control element falls to a value V.sub.FAULT, or less, and
- (2) is functionally linked to the circuit interruption element so that when the control element is in the on state, the circuit interruption element is in the closed state, and when the control element is in the off state, the circuit interruption element is in the open state;
- and
- iii. the bypass element, comprises a parallel combination of a first bypass path and a second bypass path, and has
- (1) a start-up state such that, if the circuit interruption element is in the open state and a current I.sub.NORMAL is passed through the bypass element, substantially all the current through the bypass element passes through the first bypass path, and the voltage across the control element is greater than V.sub.FAULT, and
- (2) a stopped state such that if the circuit interruption element is in the open state as a result of the voltage across the control element having fallen to a value V.sub.FAULT or less, substantially all the current through the bypass element passes through the second bypass path, and the current through the bypass element is such that the voltage across the control element remains at a value of V.sub.FAULT or less.
11 more elements
Dependencies are inferred from the claim text.