TIDUEZ1 March   2021

 

  1.   Description
  2.   Resources
  3.   Features
  4.   Applications
  5.   5
  6. 1System Description
    1. 1.1 Key System Specifications
  7. 2System Overview
    1. 2.1 Block Diagram
    2. 2.2 Design Considerations
      1. 2.2.1 Multichannel SSR with Independent Isolation Between SSR Channels
      2. 2.2.2 Design Challenge With Single Isolation
      3. 2.2.3 Multichannel SSR Drive With Single Isolation Multichannel Digital Isolator
      4. 2.2.4 Need of High-Impedance Voltage Translator
      5. 2.2.5 Design to Minimize Cross-Coupling and MOSFET Gate Pick up Due to Other SSR Switching
      6. 2.2.6 Schematic: Design of Gate-Drive Circuit
        1. 2.2.6.1 Calculation of Gate-Driver Power Consumption
      7. 2.2.7 Schematic: Digital Isolator Circuit
      8. 2.2.8 Schematic: 3.3 V to 10V_ISO, 5V_ISO Power Supply
    3. 2.3 Highlighted Products
      1. 2.3.1 ISO7760
      2. 2.3.2 ISO7740
      3. 2.3.3 ISO7041
      4. 2.3.4 CSD19538Q2
      5. 2.3.5 CSD17382F4
      6. 2.3.6 TPL7407LA
      7. 2.3.7 TLV760
      8. 2.3.8 TLC555
  8. 3Hardware, Software, Testing Requirements, and Test Results
    1. 3.1 Hardware Requirements
      1. 3.1.1 Test Equipment Needed to Validate Board
      2. 3.1.2 Test Conditions
      3. 3.1.3 Test Procedure
    2. 3.2 Test Setup
    3. 3.3 Test Results
      1. 3.3.1 Functional Tests
      2. 3.3.2 Overcurrent Testing With External Fuse
      3. 3.3.3 Surge Testing
      4. 3.3.4 Multichannel SSR Driven From Two 24-VAC Transformers
      5. 3.3.5 Alternate SSR Topology for High Voltage
  9. 4Design and Documentation Support
    1. 4.1 Design Files
      1. 4.1.1 Schematics
      2. 4.1.2 BOM
    2. 4.2 Documentation Support
    3. 4.3 Support Resources
    4. 4.4 Trademarks
  10. 5About the Author

3.3.2 Overcurrent Testing With External Fuse

The reference design is tested for short-circuit conditions with an external fuse. Figure 3-17 shows the wiring diagram during testing. The short circuit is created by shorting the relay coil (COIL-1).

GUID-20210210-CA0I-WKF6-W9S4-4DGSGXRP3XR6-low.gifFigure 3-17 Overcurrent Protection Circuit With External Fuse

Test Condition:

  • The COIL-1 is short-circuited
  • The short-circuit current at the secondary of the transformer is limited by the secondary short-circuit impedance of transformer
  • Specification of the transformer used for testing:
    • Manufacturer part number: 4000-09C02K999 (TE connectivity - laminated 20VA transformer)
    • Secondary winding resistance = 2 Ω
  • Specification of the fuse used in series with the transformer secondary line RC:
    • Manufacturer part number: 046601.5NR (Littelfuse Inc.)
    • Rating: 1.5 A, 63-V AC/DC board mount fuse, 1206
    • Response time: Fast blow. Melting I²t: 0.1103

Observations during testing:

  • During the short-circuit test, the fuse was blown within one electrical cycle (< 20 ms) with peak short-circuit current of approximately 7 A. The SSRs were functional after testing.
  • Figure 3-18 shows the test result waveforms.
GUID-20210210-CA0I-BHNX-JM6G-41MDJBLQT947-low.pngFigure 3-18 Short-Circuit Test Waveforms With External Fuse