Ground fault protection circuit

• US 6,188,553 B1
• Filed: 10/16/1998
• Issued: 02/13/2001
• Est. Priority Date: 10/10/1997
• Status: Expired due to Fees

• Current Assignee: Chicago Miniature Optoelectronic Technologies, Inc.
• Original Assignee: Electro-Mag International, Inc.
• Inventors: Moisin, Mihail S.
• Primary Examiner(s): Sherry, Michael J.
• Assistant Examiner(s): HUYNH, KIM NGOC
• Application Number:
  US09/173,981
• Time in Patent Office: 851 Days
• Field of Search: 361/42-50, 361/54, 361/78, 361/86, 361/56, 361/52, 315/127, 315/306, 315/307, 315/91
• US Class Current: 361/52
• CPC Class Codes: H02H 3/33 using summation current transformers H02H3/347 takes precedence
• CPC Class Codes: H02M 1/38 Means for preventing simultaneous conduction of switches
• CPC Class Codes: H02M 1/425 using a single converter stage both for correction of AC input power factor and generation of a high frequency AC output voltage
• CPC Class Codes: H05B 41/28 using static converters
• CPC Class Codes: H05B 41/2851 for protecting the circuit against abnormal operating conditions
• CPC Class Codes: H05B 41/2856 against internal abnormal circuit conditions
• CPC Class Codes: Y02B 70/10 Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes

Abstract

A ground fault detection circuit is coupled to an AC circuit and to earth ground for detecting a flow of energy from the AC circuit to earth ground through a path external to the AC circuit. In one embodiment, the ground fault circuit includes a detection circuit coupled to a negative rail of an inverter, which forms part of the AC circuit, and a detection control circuit coupled to the inverter for disabling the AC circuit.

Claims

1. A circuit, comprising:

an inverter circuit for providing an AC output signal to a load, the inverter circuit having first and second voltage rails;

a ground fault circuit having first and second input terminals and coupled to the first voltage rail of the inverter at said first input terminal and coupled to earth ground at said second input terminal, wherein the ground fault circuit detects a flow of current from the load to earth ground through a path external to the circuit, said ground fault circuit including a detection circuit for detecting the flow of current to earth ground and a detection control circuit for disabling the inverter to terminate the flow of current to the load,

wherein said detection circuit is a resonance circuit configured such that the flow of current therethrough generates a local resonance having a resonant frequency at or near a frequency of operation of the inverter circuit.

2. The circuit of claim 1, wherein the detection circuit provides a circuit path from the inverter to earth ground.

3. The circuit according to claim 2, wherein the circuit path includes a capacitor.

4. The circuit according to claim 3, wherein the circuit path further includes a resistor.

5. The circuit according to claim 1, wherein the local resonance includes a series resonance.

6. The circuit according to claim 1, wherein the local resonance includes a parallel resonance.

7. The circuit according to claim 1, wherein the load is fluorescent lamp.

8. The circuit according to claim 1, wherein the inverter includes at least one switching element having a conduction state controlled by a control circuit and the detection control circuit selectively causes the control circuit to bias the at least one switching element to a non-conductive state.

9. The circuit according to claim 8, wherein the detection control circuit disables the inverter when the detection circuit detects a flow of current from the load to earth ground which is greater than a predetermined threshold.

10. A method for providing ground fault protection for an inverter circuit driving a load, comprising:

providing a ground fault circuit for detecting energy flow from an inverter circuit for energizing a load to earth ground generated by a flow of current from the inverter circuit to earth ground through a path external to the inverter circuit,

configuring said ground fault circuit to include a detection circuit having circuit for generating a resonance frequency at or near the operation frequency of said inverter circuit to amplify said flow of current, and

wherein said ground fault circuit further includes a control circuit for disabling said inverter when said energy flow exceeds a selected threshold.

11. The method according to claim 10, wherein the path external to the circuit includes a human being.

12. A method for providing ground fault protection to an inverter circuit energizing a load, comprising the steps of:

detecting a common mode energy signal, generated due to a discontinuity in an AC signal path from said inverter circuit to ground, the step of detecting being performed by a ground fault circuit having a reasonable circuit for generating a local resonance frequency at or near the operation frequency of said inverter circuit; and

limiting a current to the load when said detected common mode energy signal exceeds a selected threshold.