SNLA490 March   2025 ISOM8110-Q1 , ISOM8111-Q1 , ISOM8112-Q1 , ISOM8113-Q1 , ISOM8115-Q1 , ISOM8116-Q1 , ISOM8117-Q1 , ISOM8118-Q1

 

  1.   1
  2.   Summary
  3. 1Relay Contact Sticking in OBCs
    1. 1.1 Relays Used in OBCs
    2. 1.2 Causes and Hazards of Relay Contact Sticking
  4. 2About Opto-emulators
    1. 2.1 Introduction to ISOM811x-Q1 and Key Parameters Like CTR
    2. 2.2 Performance Comparison with Optocoupler and Single-Channel Digital Isolator
  5. 3AC Relay Weld Detection in V2L Circuit for OBCs Based on ISOM8118-Q1
    1. 3.1 What Is V2L for OBCs
    2. 3.2 Design Reference for AC Relay Weld Detection Circuit in V2L
    3. 3.3 Design Examples and Selection Guidelines Based on Typical Circuits
      1. 3.3.1 Select Voltage Judgment Threshold VTH and IFmin
      2. 3.3.2 Select Current-limiting Resistor R1
      3. 3.3.3 Select the pull-up resistor R2
  6. 4Summary
  7. 5References

Abstract

With the global shift toward vehicle electrification, vehicle to load (V2L) applications are becoming more popular. The market demand for on-board chargers (OBCs) - the key component in EVs/HEVs - is also rising. Relays, a core part of OBCs, are used to connect or disconnect the power between the high-voltage AC or high-voltage DC circuits. However, frequent use and external environmental factors can cause relay contacts to weld, or stick, affecting the reliability of the OBC or even the entire vehicle. The traditional method for relay weld detection is to compare the voltages at the front and rear ends of the relay, which requires two channels of high-voltage sampling, increasing system cost and design challenges. The ISOM811x-Q1 family of opto-emulators leverages TI’s latest generation of SiO2-based isolation technology and can emulate the current-driven input structure of an optocoupler without the poor reliability of the LED. This article focuses on how to build a low-cost relay weld detection scheme with the ISOM8118-Q1, saving one voltage sampling channel and reducing system complexity.