SBAA783 January   2026 ISOM8600 , ISOM8610

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Digital Output in PLC/DCS, Motor Drives and Robotics
    1. 1.1 Sink and Source Outputs: Supports Bidirectional Operation
    2. 1.2 PLC/DCS
    3. 1.3 Motor Drives
    4. 1.4 Robotics
  5. 2Design Procedures for Driving a Relay (Inductive Load)
    1. 2.1 Introduction to a Mechanical Relay
    2. 2.2 ISOM8600 Design Example
    3. 2.3 Test Results based on ISOM8600 and relay
      1. 2.3.1 Test 1: No Protection
      2. 2.3.2 Test 2: Capacitive Filter
      3. 2.3.3 Test 3: Zener Active Clamping Diode
  6. 3ISOM86x0 Advantages
    1. 3.1 Isolation Technology
    2. 3.2 Opto-Emulator Signal Chain
  7. 4Summary
  8. 5References

2.3 Test Results based on ISOM8600 and relay

One important consideration for design is the VOFF of the output when driving a relay or an inductive load. The ISOM8600 supports up to VOFF = 80VDC, however, the free-wheeling voltage (or back EMF) when the ISOM8600 output stops driving the relay coil can cause a transient up to 150VPK. Therefore, additional protection is needed to resolve this challenge.

The energy from the 24V supply is stored in the mechanical relay coil while the output (P1 and P2) is ON. The back EMF is the released coil energy that appears at pin 4 when the output (P1 and P2) switches OFF.

Two common mechanical relays were selected to test the circuit in Figure 2-1 to demonstrate this challenge. The first test shows the free-wheeling voltage generated from the mechanical relay.