How to Select the Right Power Supply for a DC Servo Motor

2025/11/18
Range of DC Servo Motors
Select the right power supply for DC servo motors. Ensure fast response, clean output, and safety with e-Fuses for robotics and automation systems.

Figure is climbing the next step. Challenge
  • Right power rating
  • Ripple and noise
  • Performance
  • Safety

Dartboard with arrow in the center Solution
  • Power supply with adequate capacity, protection features, fast load response, clean output
  • Adjustable e-Fuse

Hand pointing with index finger Application
  • Robotics
  • Manufacturing systems
  • Positioning
  • Gate Machines

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Introduction

When designing a system that uses DC servo motors, selecting the right power supply is essential to ensure reliable performance and protect system components. DC servo motors, which commonly operate within a 24VDC to 48VDC range, require a power supply that can handle their unique requirements, such as precise voltage regulation, adequate current delivery, and protection mechanisms. This article provides a comprehensive guide to selecting an appropriate power supply and incorporating an electronic fuse (e-Fuse) for optimal safety and performance.

Understanding DC Servo Motor Requirements

Typical Motor Current under acceleration, constant speed and deceleration
Fig. 1: Typical Motor Current under acceleration (red), constant speed (green) and deceleration (blue). Note that the motor current can be negative due to back EMF
Servo motors are widely used in industrial automation, robotics, and precision equipment due to their ability to deliver high torque, accurate positioning, and excellent speed control. Before choosing a power supply, it is essential to understand the motor’s electrical characteristics:

  • Voltage Range: As noted earlier, DC servo motors typically operate within a rated voltage range (e.g., 24VDC to 48VDC). The power supply must maintain a stable voltage level within this range to ensure consistent and reliable motor operation.

  • Current Requirements: Servo motors draw different currents depending on their load. Consider the motor’s continuous operating current and the peak current during start-up or under heavy-load conditions to ensure that the power supply can handle these demands (figure 1).

  • Ripple and Noise: Motors are sensitive to voltage ripples and electrical noise, which can negatively impact their performance. Using a power supply with a low ripple and noise levels is crucial for smooth motor operation.

Key Factors for Power Supply Selection

Voltage and Current Ratings

Select a power supply that delivers a stable voltage within the motor’s operating range. For the current, ensure that the supply can handle the motor’s peak demands. For example, if a motor requires up to 10A of continuous current and 20A during start-up, choose a power supply rated for the 10A continuous output but capable of delivering at least 20A peak current for the start-up period (typically 20-30ms).

Power Capacity

Calculate the average continuous power requirement (Pcont.) with Equation (1):

Pcont. = V x Imax. cont.

Where V is voltage, and Imax. cont. is the maximum continuous current. Add a margin of about 20% to 30% to account for transient loads. For example, a motor requiring 24VDC and 8A, the power supply should provide at least 24 x 8 = 192W continuous power. When including the margin, the power supply should provide 250W for at least 10s. Allow for power derating with worst case ambient temperature.

Dynamic Load Response

Servo motors often operate with rapidly changing loads. The power supply must respond quickly to these changes without excessive voltage dips or overshoots.

Back EMF

If the momentum of a spinning load drives the motor, it can act as a generator and feed a back EMF voltage into the power supply output. The power supply must be capable of withstanding a back EMF voltage of up to 150% of its nominal output voltage. For example, a 24V supply should be able to tolerate up to 36V on its output without damage.

Protection Features

Over-voltage (OV), under-voltage (UV), over-current (OC), and thermal protections are essential to safeguard both the motor and power supply from damage.

Efficiency

High-efficiency power supplies reduce heat generation and energy consumption, improving the system’s overall reliability and lowering operating costs.

Incorporating an e-Fuse for Additional Protection

An electronic fuse (e-Fuse) is a modern protection device that safeguards both the motor and power supply from electrical faults.

Benefits of an e-Fuse

  • Individual Over-Current Protection (OCP): Automatically disconnects the affected circuit during excessive current draw without interfering with the remaining circuits.
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  Series
1 AC/DC, 4 Channels Output, DIN-Rail RACPRO1-4SP Series
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  • Push-in connectors for tool-less wiring
  • Start-Up delay adjustable by switch
  • NEC Class 2 limit switchable (for 5A module)
  • Adjustable power limit & load indication by LED
2 AC/DC, 240 W, Single Output, DIN-Rail RACPRO1-S240 Series
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  • DC 入力電圧範囲 88-370VDC