4.2.2 A proposed fail-safe relay drive circuit for motor current cut-off control
For the purpose of wider application of the above-mentioned motor current cut-off function, a fail-safe relay driver circuit shown in Figure 4.4 is proposed. The basic diagram of the fail-safe relay driver is shown in Figure 4.3. The circuit consists of CMOSs, transformers and general electronic devices, i.e. resistances and capacitors as well as a general IC, and no CPUs are used, as shown in figure 4.5. No utilization of CPUs to safety-related applications is beneficial because, and this applies to other applications [32, 45], there is no need to provide the subsidiary safety measures for CPUs, which contributes considerably to simplification of relay drive circuits embedded in motor drive control systems[52-53].