14 SERVO MOTOR DRIVE CIRCUITS https://bourns.com/ Issue 3 2025 Power Electronics Europe www.power-mag.com Protection and Layout Considerations to Maximize Efficiency in Servo Motor Drive Circuits Servo motors convert electrical energy into precise mechanical motion making them essential components in today’s motion control systems. Their widespread use spans from household appliances to industrial automation, where high-performance and accuracy are required. Known for their superior efficiency and responsiveness, servo motors are typically driven by high-frequency AC voltage, which necessitates specialized power conversion circuitry. To deliver the appropriate power to these motors, a combination of stages is used to convert and condition electrical energy. These stages perform everything from rectifying AC mains, correcting power factor, and generating high-frequency signals, to providing robust protection and accurate feedback. Each stage presents design challenges that can include a reduction in power quality, the need to deal with electromagnetic interference, conditions that require additional thermal management measures, and added requirements for effective surge protection. This article explores the components required along with the layout considerations in designing servo motor drive circuits. It focuses on the power conversion, circuit protection, and current sensing components that are employed to help designers enhance performance, reliability, and efficiency. Whether powering a compact servo in a precision tool or a large industrial motor, the principles outlined here serve as a foundation for creating robust and energy-efficient drive systems. Servo Motor Drive Circuits Layout The most common application of a servo motor circuit is to convert AC main power into a significantly higher frequency to drive AC or DC servo motors. Figure 1 shows a block diagram of a typical servo motor drive circuit. As shown, the circuit uses a full-bridge rectifier with a filtering capacitor to transform the AC signal into a DC voltage. However, due to the rectified nature of the DC voltage, there are highvalue current harmonics present within the power. The presence of these current harmonics can potentially cause outages in the connecting power grid. To prevent outages, Power Factor Correction (PFC) circuits are implemented to increase the power factor. An H-bridge then converts the DC bus voltage after the rectification and PFC stages to a workable PWM or AC singlephase waveform for the motor. The Hbridge can be replaced for a three-phase, half-bridge design that incorporates similar characteristics but designed for threephase motors. These connected circuits are typically controlled and monitored by a microcontroller, which handles and operates the high-precision operation of the motor drive circuit. By using a servo motor drive circuit, power is conserved by converting a low-frequency input into a high-frequency signal suitable for servo motor applications. Power Protection Incoming power from the electrical grid is vulnerable to frequent overvoltage and overcurrent events, which pose a risk to drive circuits. Caused by lightning strikes, grid switching transients, or inductive kickback, these surge events are often thousands of volts and amps; much higher than the rated voltages of any connected Figure 1. Block diagram of circuits that make up a servo motor drive circuit.
RkJQdWJsaXNoZXIy MjQ0NzM=