Apparatus and method for detecting ground fault
First Claim
1. A ground fault detector for a cold cathode tube comprising:
- a resistive path connected to a secondary side of a high-voltage transformer providing power to a cold cathode tube, said resistive path being arranged to provide a ground fault path to ground fault current causing ground fault voltage to be developed across said ground fault path during a ground fault condition, the ground fault voltage being in phase with the ground fault current;
a detection circuit, connected to said resistive path to receive voltage corresponding to the ground fault voltage, constructed and arranged to provide an output representing a fault detection signal upon detecting that said voltage is larger than a threshold value;
an isolation circuit, connected to said detection circuit, constructed and arranged to isolate said fault detection signal from a primary side of said high voltage transformer; and
a stop latch including an input connected to said isolation circuit and an output connected to a power supply arranged to supply power to said primary side of said high-voltage transformer.
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Accused Products
Abstract
An electrical power system for a cold cathode tube includes a high-voltage transformer with a primary side connected to a power supply and a secondary side connected to a cold cathode tube and includes a ground fault detector. The ground fault detector includes a resistive path, a detection circuit, an isolation circuit, and a stop latch. The resistive path is connected to the secondary side of the high-voltage transformer and is arranged to provide a ground fault path to ground fault current. The detection circuit is connected to the resistive path and is constructed and arranged to provide an output representing a fault detection signal. The isolation circuit is connected to the detection circuit and is constructed and arranged to isolate the fault detection signal from the primary side of the high voltage transformer. The stop latch has an input connected to the isolation circuit and an output connected to the power supply and is constructed and arranged to generate an inhibition signal for inhibiting operation of the power supply.
62 Citations
18 Claims
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1. A ground fault detector for a cold cathode tube comprising:
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a resistive path connected to a secondary side of a high-voltage transformer providing power to a cold cathode tube, said resistive path being arranged to provide a ground fault path to ground fault current causing ground fault voltage to be developed across said ground fault path during a ground fault condition, the ground fault voltage being in phase with the ground fault current; a detection circuit, connected to said resistive path to receive voltage corresponding to the ground fault voltage, constructed and arranged to provide an output representing a fault detection signal upon detecting that said voltage is larger than a threshold value; an isolation circuit, connected to said detection circuit, constructed and arranged to isolate said fault detection signal from a primary side of said high voltage transformer; and a stop latch including an input connected to said isolation circuit and an output connected to a power supply arranged to supply power to said primary side of said high-voltage transformer. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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11. A power supply system for a cold cathode tube comprising:
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a high-voltage transformer including a primary side and a secondary side connected to a cold cathode tube; an inverter power supply constructed and arranged to provide power to said primary side of said high-voltage transformer; a resistive path connected to said secondary side and arranged to provide a ground fault path to ground fault current during a ground fault condition, said ground fault current generating voltage across said ground fault path, said voltage being in phase with said ground fault current; a detection circuit constructed and arranged to provide a fault detection signal upon detecting that said voltage is larger than a threshold value; a isolation circuit constructed and arranged to isolate said voltage from said primary side of said high voltage transformer; and a latch circuit constructed and arranged to inhibit said inverter power supply upon receiving a signal representing said ground fault condition. - View Dependent Claims (12, 13)
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14. A method for detecting a ground fault in a power supply for a cold cathode tube including the steps of:
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generating a power signal; supplying said power signal to a primary side of a high-voltage transformer and receiving high voltage power by a cold cathode tube from a secondary of said high-voltage transformer; providing a resistive ground path for ground fault current from said secondary side of said high voltage transformer, the ground fault current creating ground fault voltage across the ground path during a ground fault condition, the ground fault voltage being in phase with the ground fault current; receiving said ground fault voltage generated by said ground fault current flowing across said ground fault path; detecting a fault condition based on said ground fault voltage being larger than a threshold voltage and generating a fault detection signal; isolating said fault detection signal from said primary side of said high voltage transformer and generating an inhibition signal; and inhibiting generation of said power signal in response to said inhibition signal. - View Dependent Claims (15, 16, 17, 18)
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Specification