Device for preventing an electrical equipment from re-powering after recovery of service interruption
First Claim
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1. A security device for electrical equipment having a power switch, the electrical equipment being connected to a power source in use, said device comprising:
- a first voltage detection circuit, operable under a first condition when the electrical equipment is supplied with power from the power source, for detecting a voltage of the power source and outputting a first detection voltage;
a second voltage detection circuit, operable under a second condition when the electrical equipment is supplied with power from the power source and when the power switch is turned on to allow the electrical equipment to be powered by the power source, for detecting a voltage of the power source and outputting a second detection voltage;
a comparator connected to said first voltage detection circuit to receive the first detection voltage and also connected to said second voltage detection circuit to receive the second detection voltage, said comparator comparing the first detection voltage with the second detection voltage and outputting a comparison result, said comparison result differing depending on whether said power source is operating under a normal powering condition or whether power has been restored following a power disruption while said power switch is in a closed position; and
control means for controlling the electrical equipment so as not to be powered by the power source in response to the comparison result obtained after power has been restored following a power disruption while said power switch is in a closed position.
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Abstract
Re-powering an electrical equipment after recovery of service interruption is prevented if the power switch of the electrical equipment stays in ON position. During a transit period of time just after recovery of service interruption, the detection voltage from a post-voltage detection circuit is set to exceed the detection voltage from a pre-voltage detection circuit. In this condition, a photo triac connected in series to the power switch is rendered non-conductive so that the electrical equipment will not be energized.
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Citations
9 Claims
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1. A security device for electrical equipment having a power switch, the electrical equipment being connected to a power source in use, said device comprising:
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a first voltage detection circuit, operable under a first condition when the electrical equipment is supplied with power from the power source, for detecting a voltage of the power source and outputting a first detection voltage; a second voltage detection circuit, operable under a second condition when the electrical equipment is supplied with power from the power source and when the power switch is turned on to allow the electrical equipment to be powered by the power source, for detecting a voltage of the power source and outputting a second detection voltage; a comparator connected to said first voltage detection circuit to receive the first detection voltage and also connected to said second voltage detection circuit to receive the second detection voltage, said comparator comparing the first detection voltage with the second detection voltage and outputting a comparison result, said comparison result differing depending on whether said power source is operating under a normal powering condition or whether power has been restored following a power disruption while said power switch is in a closed position; and control means for controlling the electrical equipment so as not to be powered by the power source in response to the comparison result obtained after power has been restored following a power disruption while said power switch is in a closed position. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. A security device for electrical equipment having a power switch, the electrical equipment being connected to a power source in use, said device comprising:
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a first status detection circuit for detecting a first status in which the electrical equipment is supplied with power from the power source, and outputting a first detection signal indicative of the first status; a second status detection circuit for detecting a second status in which the electrical equipment is supplied with power from the power source and the power switch is turned on to allow the electrical equipment to be powered by the power source, and outputting a second detection signal indicative of the second status; and switching means connected in series to the electrical equipment, said switching means being selectively rendered ON or OFF according to a combination of the first detection signal and the second detection signal, wherein said switching means is rendered OFF when the first detection signal and the second detection signal have a combination of outputs which indicates that power has been restored following a power disruption while said power switch is in a closed position. - View Dependent Claims (9)
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Specification