TIDUF85 August   2024

 

  1.   1
  2.   Description
  3.   Resources
  4.   Features
  5.   Applications
  6.   6
  7. 1System Description
    1. 1.1 Key System Specifications
  8. 2System Overview
    1. 2.1 Block Diagram
      1. 2.1.1 Subsystems
        1. 2.1.1.1 Arc Detection Channels
          1. 2.1.1.1.1 Isolated Current Measurement
          2. 2.1.1.1.2 Band-Pass Filter
          3. 2.1.1.1.3 Analog-to-Digital Conversion
          4. 2.1.1.1.4 Arc Detection Using Embedded AI Models
        2. 2.1.1.2 Arc Labeling Circuit
          1. 2.1.1.2.1 Isolated String Voltage Measurement
          2. 2.1.1.2.2 Isolated Arc Voltage Measurement With Isolated Comparator
          3. 2.1.1.2.3 Window Comparator for Advanced Labeling
    2. 2.2 Design Considerations
      1. 2.2.1 Current Sensor and Input Stage
      2. 2.2.2 Analog Band-Pass Filter
      3. 2.2.3 Arc-Labeling Circuit
        1. 2.2.3.1 String Voltage Sensing
        2. 2.2.3.2 Arc Gap Voltage Sensing
        3. 2.2.3.3 Differential to Single-Ended Conversion
        4. 2.2.3.4 Window Comparator for Arc Labeling
      4. 2.2.4 Auxiliary Power Supply
      5. 2.2.5 controlCard and Debug Interface
    3. 2.3 Highlighted Products
      1. 2.3.1 TMDSCNCD28P55X – TMDSCNCD28P55X controlCARD Evaluation Module
        1. 2.3.1.1 Hardware Features
      2. 2.3.2 OPA4323 – Quad, 5.5V, 20MHz, Zero-Cross Low-Noise (6nV/√Hz) RRIO Operational Amplifier
      3. 2.3.3 OPA323 – Single, 5.5V, 20MHz, Zero-Cross Low-Noise (6nV/√Hz) RRIO Operational Amplifier
      4. 2.3.4 AMC3330 – ±1V Input, Precision Voltage Sensing Reinforced Isolated Amplifier With Integrated DC/DC
      5. 2.3.5 AMC23C11 – Fast-Response, Reinforced, Isolated Comparator With Adjustable Threshold and Latch Function
  9. 3Hardware, Testing Requirements, and Test Results
    1. 3.1 Signal Chain Verification
      1. 3.1.1 Hardware Requirements
      2. 3.1.2 Test Setup
      3. 3.1.3 Test Results
    2. 3.2 Arc Testing
  10. 4Design and Documentation Support
    1. 4.1 Design Files
      1. 4.1.1 Schematics
      2. 4.1.2 BOM
    2. 4.2 Tools and Software
    3. 4.3 Documentation Support
    4. 4.4 Support Resources
    5. 4.5 Trademarks
  11. 5About the Author

2.2.3.4 Window Comparator for Arc Labeling

A window comparator is implement using the dual channel amplifier TLV9022. This circuit is used for arc labeling in addition with AMC23C11. While AMC23C11 provides a very fast response for when the arc starts, cannot detect when the arcing stops. Since after the arcing the arc gap voltage still be higher than the threshold. Here the window comparator circuit comes into play. allows to indicate the start of an arc, as soon as the arc voltage rises above the lower threshold and the end of an arc as soon as the arc rises above the upper threshold. Both thresholds are set with relative to the string voltage using R3, R42 and R48. The lower threshold is described in Equation 5.

Equation 5. V TH_L = V String × 3 kΩ ( 43 kΩ + 27 kΩ + 3 kΩ ) ≈ V String × 0 . 041

The upper threshold is described inEquation 6.

Equation 6. V TH_H = V String × ( 27 kΩ + 3 kΩ ) ( 43 kΩ + 27 kΩ + 3 kΩ ) ≈ V String × 0 . 41
Note: VString is the output of the differential to single-ended conversion circuit and not the input voltage.

When applying these formulas to the actual input voltages for the string voltage VString_IN and arc gap voltage VArc_IN we need to take the different voltage gains of the two sensing circuits into account.

Equation 7. V ARC_TH_L = V String _ IN × 0 . 0062 0 . 0205 × 3 kΩ ( 43 kΩ + 27 kΩ + 3 kΩ ) ≈ V String_IN × 0 . 0124
Equation 8. V ARC_TH_H = V String _ IN × 0 . 0062 0 . 0205 × ( 27 kΩ + 3 kΩ ) ( 43 kΩ + 27 kΩ + 3 kΩ ) ≈ V String_IN × 0 . 124

As an example, for a string voltage VString_IN of 800V, the lower threshold VARC_TH_L is about 10V and the higher threshold VARC_TH_H is about 100V. This means if the arc gap voltage VArc_IN is between 10V and 100V the window comparator indicates that an arc is present.

TIDA-010955 Schematics Window Comparator Circuit for Arc Labeling Figure 2-9 Schematics Window Comparator Circuit for Arc Labeling