Operational amplifier circuit and arc fault circuit interrupter including the same

• US 8,004,802 B2
• Filed: 11/19/2008
• Issued: 08/23/2011
• Est. Priority Date: 11/19/2008
• Status: Active Grant

• Current Assignee: Eaton Intelligent Power Limited (Eaton Corporation PLC.)
• Original Assignee: Eaton Corp. (Wisconsin) (Eaton Corporation PLC.)
• Inventors: Elms, Robert T.
• Primary Examiner(s): Fureman; Jared
• Assistant Examiner(s): Thomas; Lucy
• Application Number:
  US12/273,993
• Publication Number:
  US 20100123983A1
• Time in Patent Office: 1,007 Days
• Field of Search: 361/42, 361/2
• US Class Current: 361/42
• CPC Class Codes: H02H 1/0015 Using arc detectors
• CPC Class Codes: H03F 2200/102 A non-specified detector of a signal envelope being used in an amplifying circuit
• CPC Class Codes: H03F 2200/321 Use of a microprocessor in an amplifier circuit or its control circuit
• CPC Class Codes: H03F 2203/45518 the FBC comprising one or more diodes and being coupled between the LC and the IC
• CPC Class Codes: H03F 2203/45526 the FBC comprising a resistor-capacitor combination and being coupled between the LC and the IC
• CPC Class Codes: H03F 3/45475 using IC blocks as the active amplifying circuit

Abstract

An operational amplifier circuit is for an arc fault circuit interrupter including a current sensor having a secondary and an envelope detector circuit having an input. The operational amplifier circuit includes a band pass filter having an input structured to be electrically interconnected with the secondary of the current sensor and an output; and a rectifier circuit. The rectifier circuit includes an operational amplifier having an input electrically interconnected with the output of the band pass filter and an output, a half-wave rectifier having an input electrically interconnected with the output of the operational amplifier, an output, and a forward voltage between the input and the output of the half-wave rectifier, the half-wave rectifier output being structured to be electrically interconnected with the input of the envelope detector circuit, and a voltage compensation circuit cooperating with the input and the output of the operational amplifier to compensate for the forward voltage.

Claims

1. An operational amplifier circuit for an arc fault circuit interrupter comprising a current sensor including a secondary and a processor including a number of inputs, said operational amplifier circuit comprising:

a band pass filter comprising an input structured to be electrically interconnected with the secondary of said current sensor and an output;

a rectifier circuit comprising;

an operational amplifier comprising an input electrically interconnected with the output of said band pass filter and an output,

a half-wave rectifier comprising an input electrically interconnected with the output of said operational amplifier, an output, and a forward voltage between the input and the output of said half-wave rectifier, and

a voltage compensation circuit cooperating with the input and the output of said operational amplifier to compensate for said forward voltage; and

an envelope detector circuit comprising an input electrically interconnected with the output of said half-wave rectifier and an output structured to be input by one of the number of inputs of said processor,

wherein said envelope detector circuit further comprises an averaging circuit including an input electrically connected to the output of said envelope detector circuit and an output structured to output a short term average value signal to one of the number of inputs of said processor.

2. The operational amplifier circuit of claim 1 wherein said band pass filter further comprises a capacitor, an inductor and a resistor;

and wherein the capacitor is electrically connected in parallel with the series combination of the inductor and the resistor.

3. The operational amplifier circuit of claim 1 wherein said half-wave rectifier further comprises a first diode including an anode;

wherein said voltage compensation circuit comprises a second diode matched with the first diode and including an anode and a cathode, a resistor electrically interconnected in series with said second diode and a capacitor electrically connected in parallel with said second diode;

wherein the anodes of said first and second diodes are electrically connected to the output of said operational amplifier; and

wherein the cathode of said second diode is electrically connected to the input of said operational amplifier.

4. The operational amplifier circuit of claim 3 wherein the output of said operational amplifier includes a first voltage;

wherein the input of said operational amplifier includes a second smaller voltage; and

wherein the first voltage less the second smaller voltage is equal to the forward voltage between the input and the output of said half-wave rectifier.

5. The operational amplifier circuit of claim 1 wherein said envelope detector circuit further comprises a first resistor including a first end and a second end, a second resistor and a capacitor;

wherein the first end of said first resistor is electrically connected to the output of said half-wave rectifier;

wherein the second end of said first resistor is structured to be electrically connected to one of the number of inputs of said processor; and

wherein the parallel combination of said second resistor and said capacitor is electrically connected between the second end of said first resistor and a ground reference.

6. The operational amplifier circuit of claim 5 wherein said second resistor and said capacitor provide a time constant of about 0.02 mS;

and wherein said envelope detector circuit is responsive to a frequency range up to about 8 kHz, in order to provide a filtered envelope signal at the output thereof.

7. The operational amplifier circuit of claim 1 wherein said averaging circuit comprises a resistor electrically connected between the input and the output of said averaging circuit and a capacitor electrically connected between the output of said averaging circuit and a ground reference.

8. The operational amplifier circuit of claim 7 wherein said resistor and said capacitor provide a time constant of about 0.22 mS.

9. The operational amplifier circuit of claim 7 wherein said resistor and said capacitor are structured to output a short term average of the output of said operational amplifier, in order to reflect both magnitude and duty cycle of the output of said operational amplifier.

10. The operational amplifier circuit of claim 1 wherein said operational amplifier circuit is structured to discriminate between first high frequency noise of a first duration and second high frequency noise of a longer second duration.

11. The operational amplifier circuit of claim 10 wherein said first high frequency noise is a number of bursts of high frequency noise caused by motor brush commutation;

and wherein said second high frequency noise is a sustained arcing event.

12. The operational amplifier circuit of claim 1 wherein said operational amplifier includes a gain-bandwidth of about 10 MHz.

13. The operational amplifier circuit of claim 1 wherein said operational amplifier includes a slew rate of at least 10 MHz.

14. The operational amplifier circuit of claim 1 wherein said operational amplifier includes a maximum power consumption of about 750 μ

A.

15. The operational amplifier circuit of claim 1 wherein said operational amplifier circuit is structured to provide a signal detection range having a full scale value and a minimum value of less than 3% of said full scale value.

16. An arc fault circuit interrupter comprising:

separable contacts;

an operating mechanism structured to open and close said separable contacts;

an arc fault detector structured to determine an arc fault trip condition operatively associated with said separable contacts, said arc fault detector comprising;

a current sensor structured to sense a current flowing through said separable contacts, said current sensor including a secondary,

a processor including a number of inputs and an output,

a band pass filter comprising an input electrically interconnected with the secondary of said current sensor and an output,

a rectifier circuit comprising;

an operational amplifier comprising an input electrically interconnected with the output of said band pass filter and an output,

a half-wave rectifier comprising an input electrically interconnected with the output of said operational amplifier, an output, and a forward voltage between the input and the output of said half-wave rectifier, and

a voltage compensation circuit cooperating with the input and the output of said operational amplifier to compensate for said forward voltage, and

an envelope detector circuit comprising an input electrically interconnected with the output of said half-wave rectifier and an output electrically interconnected to one of the number of inputs of said processor,

wherein said envelope detector circuit further comprises an averaging circuit including an input electrically connected to the output of said envelope detector circuit and an output structured to output a short term average value signal to one of the number of inputs of said processor; and

a trip mechanism cooperating with the output of said processor and said operating mechanism to trip open said separable contacts responsive to said determined arc fault trip condition.

17. The arc fault circuit interrupter of claim 16 wherein said half-wave rectifier further comprises a first diode including an anode;

wherein said voltage compensation circuit comprises a second diode matched with the first diode and including an anode and a cathode, a resistor electrically connected in series with said second diode and a capacitor electrically connected in parallel with said second diode;

wherein the anodes of said first and second diodes are electrically connected to the output of said operational amplifier; and

wherein the cathode of said second diode is electrically connected to the input of said operational amplifier.

18. The arc fault circuit interrupter of claim 17 wherein the output of said operational amplifier includes a first voltage;

wherein the input of said operational amplifier includes a second smaller voltage; and

wherein the first voltage less the second smaller voltage is equal to the forward voltage between the input and the output of said half-wave rectifier.

19. The arc fault circuit interrupter of claim 16 wherein said arc fault detector is structured to discriminate between first high frequency noise of a first duration and second high frequency noise of a longer second duration.

20. The arc fault circuit interrupter of claim 16 wherein said operational amplifier includes a gain-bandwidth of about 10 MHz;

and wherein said arc fault detector is structured to provide a signal detection range having a full scale value and a minimum value of less than 3% of said full scale value.

21. An operational amplifier circuit for an arc fault circuit interrupter comprising a current sensor including a secondary, a processor including a number of inputs, and an envelope detector circuit comprising an input and an output structured to be input by one of the number of inputs of said processor, said operational amplifier circuit comprising:

a band pass filter comprising an input structured to be electrically interconnected with the secondary of said current sensor and an output;

a rectifier circuit comprising;

an operational amplifier comprising an input electrically interconnected with the output of said band pass filter and an output,

a half-wave rectifier comprising an input electrically interconnected with the output of said operational amplifier, an output, and a forward voltage between the input and the output of said half-wave rectifier, the output of said half-wave rectifier being structured to be electrically interconnected with the input of said envelope detector circuit, and

a voltage compensation circuit cooperating with the input and the output of said operational amplifier to compensate for said forward voltage; and

an averaging circuit including an input structured to be electrically connected to the output of said envelope detector circuit and an output structured to output a short term average value signal to one of the number of inputs of said processor.