16 SERVO MOTOR DRIVE CIRCUITS https://bourns.com/ Issue 3 2025 Power Electronics Europe www.power-mag.com SiC Schottky barrier diodes can also be used to increase power efficiency for most systems. SiC diodes exhibit negligible reverse recovery charge (Qrr). This drastically reduces switching losses in the PFC switching element where reverse recovery of the diode would otherwise cause high losses and EMI in Si-based solutions. SiC devices can also operate at higher junction temperatures (often up to 175° C), reducing the need for bulky heat sinks or forced-air cooling. PFC designs can be tricky, but with proper tuning of the frequency, duty cycle, and values of the inductor and filtering capacitor, it is possible to make the current waveform resemble a sinusoidal waveform that is in phase with the AC main voltage. By using a PFC circuit, the unintended effects of a servo motor are minimized, reducing costs in maintenance and electricity fees. Implementing an H-Bridge Once the incoming power has been filtered and passed through the PFC, the power must be reconverted into a highfrequency AC or trapezoidal waveform. An H-bridge configuration is commonly used to convert DC power into a high-frequency signal. The H-bridge uses high frequency PWM signals to control high-performance transistors, similar to the operation of IGBTs. The frequency in an H-bridge is often adjustable, allowing for precision speed and torque control of the motor. Accurate Current Sensing The servo motor drive circuit requires almost constant measurement and adjustment of the switching frequencies of the PFC and the H-bridge, as they are critical motor control operational elements. The most important measurement is the current sensing of the various stages of power conversion. The preferred current sensing solution for servo motor circuits is its high-powered current sensing shunts. These robust devices are known to excel at delivering high precision current measurement. Current shunt resistors operate by providing a low voltage drop through an accurate resistance. By measuring the voltage drop across the resistor, the current can be calculated and monitored. Constant current sensing is required in motor drive circuits as they use a closed-loop feedback system that helps maintain efficient operation. Benefits Servo motor drive circuits are essential in modern motion control systems requiring precise power conversion, protection, and control. The key stages of a typical drive circuit—from rectification and power factor correction to high-frequency AC and trapezoidal generation and current sensing present unique challenges. To remedy the identified harmonic distortion, surge vulnerability, and efficiency loss issues presented, servo motor drive circuits require a high-performance, integrated protection design that can meet manufacturers’ efficiency and control goals. Key components are SPDs that provide robust and rugged solutions that can withstand potentially damaging overvoltage and overcurrent events. Another component in the protection arsenal are today’s innovative hybrid protection devices, which combine the fast clamping of MOVs with the low capacitance of GDTs. In addition, IGBTs and SiC diodes support high-frequency switching in PFC and H-bridge stages, reducing power losses, and enabling higher motor speeds. Plus, advanced current sensing shunts provide a high-precision solution for realtime control feedback necessary in servo motors. These components allow designers to build more compact and accurate servo motor drive circuits that meet ongoing requirements for greater control or adjustment capabilities in increasingly expensive industrial motors as well as in small servo motors. As servo motor applications continue to expand across automation, robotics, and electric mobility, the importance of reliable drive circuit design will only grow necessitating ever more advanced protection devices to safeguard these essential control systems. To receive your own copy of Power Electronics Europe subscribe today at: www.power-mag.com Bourns® SiC Schottky diodes enable designers to increase power efficiency and decrease noise in PFC designs.
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