According to the drive requirements of the ABS system for electric pumps, the pump drive motor will supply oil to the accumulator when the pipeline is depressurized to ensure its high pressure state. The system chose to use relays to control the working and stopping status of the motor. Selection of the relay: According to the working voltage and working current of the pump drive motor and the working voltage and working current of the contact, the type J2C-21F / 012 was selected. The electrical parameters are: rated working voltage: 12V (DC), coil resistance is 400Ω, pull-in voltage is 9.8V, and the power consumed by the coil is 0.36W. The contact load voltage is 28V, and the current is 3A. The circuit and diagram are as shown. According to the rated operating voltage and rated working current of the relay, the working current of the relay can be determined as: 30mA, 7407 can input 10 ~~ 15mA to the photocoupler The current transfer ratio of the TIL117 of the coupler is 50%, so its output current is 5mA ~~ 10mA. The current amplification through the transistor can meet the current driving requirements.