Method and apparatus for protecting monitor circuit from fault condition
First Claim
1. A monitor circuit comprising:
- an input protection circuit comprising;
a first input;
a second input coupled to ground, and a fault interrupt device coupled between the first input and a control node, the fault interrupt device configured to protect the monitor circuit from a fault condition on the first input; and
an isolated output section coupled to the input protection section via the control node, the isolated output section configured to produce an output signal upon the occurrence of a triggering event at the first input, wherein, the monitor circuit is configured to produce the output signal even while in the fault condition.
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Accused Products
Abstract
A method and apparatus for improving the fault protection of a monitor circuit is provided by coupling an input protection circuit to an output section. The input protection circuit may include a fusible device that limits or removes a fault condition present at an input to the input protection circuit. The fusible device may be, for example, a resettable positive temperature coefficient (“PTC”) device configured to limit the current passing through it to a predetermined level once it reaches a predetermined temperature. A resistive element may be thermally coupled to the PTC device to assist it reaching the predetermined temperature. The monitor circuit may further be configured to generate a sensory signal in response to a fault condition.
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Citations
40 Claims
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1. A monitor circuit comprising:
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an input protection circuit comprising;
a first input;
a second input coupled to ground, and a fault interrupt device coupled between the first input and a control node, the fault interrupt device configured to protect the monitor circuit from a fault condition on the first input; and
an isolated output section coupled to the input protection section via the control node, the isolated output section configured to produce an output signal upon the occurrence of a triggering event at the first input, wherein, the monitor circuit is configured to produce the output signal even while in the fault condition. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16)
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17. An alarm system comprising a controller, the controller comprising:
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a processor;
a memory device; and
a monitor circuit comprising;
an input protection circuit having a first input, a second input coupled to ground, and a fault interrupt device coupled between the first input and a control node, the fault interrupt device configured to protect the monitor circuit from a fault condition on the first input; and
an isolated output section coupled to the input protection section via the control node, the isolated output section configured to produce an output signal upon the occurrence of a triggering event at the first input, wherein, the monitor circuit is configured to produce the output signal even while in the fault condition. - View Dependent Claims (18, 19, 20, 21, 22, 23, 24, 25, 26, 27)
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28. A method of fault protecting a monitor circuit having an input protection circuit coupled to an output section at a control node, the method comprising:
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during a first half cycle of a fault condition present on a first input of the input protection circuit, blocking a voltage at the first input; and
during a second half cycle of the fault condition, limiting a current between the first input and the control node to a predetermined current level and setting the voltage at the control node to a predetermined voltage level. - View Dependent Claims (29, 30, 31, 32, 33)
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34. A method of fault protecting a monitor circuit having an input protection circuit coupled to an output section at a control node, the method comprising:
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during a first half cycle of a fault condition present on a first input of the input protection circuit, setting a voltage at the control node to a first predetermined voltage level; and
during a second half cycle of the fault condition, setting the voltage at the control node to a second predetermined voltage level and limiting a current between the first input and the control node to a predetermined current level. - View Dependent Claims (35, 36, 37, 38, 39, 40)
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Specification