Designing a power-supply system for industrial automation equipment requires a thorough understanding of the surroundings and conditions that affect the functionality of the wide range of equipment involved. The most important design decision is whether to use linear power supplies or switch-mode power supplies (SMPS).
Today, SMPS are the most popular because of their high efficiency. However, they do have downsides that make linear supplies more desirable. Linear supplies also have their disadvantages, but often turn out to be the best choice for industrial use. Even better is a “have your cake and eat it too” solution: Use a linear supply with low-dropout (LDO) regulators.
Linear vs. SMPS
As mentioned, the primary reason for using switch-mode supplies is their high efficiency. Typical figures vary with the application, but efficiencies of greater than 90% are typical. High efficiency translates into minimum power loss in the supply with its attendant low heat dissipation. In large complex industrial settings with lots of equipment efficiency, power usage and heat dissipation become critical factors in terms of operating costs.
The main disadvantage of the SMPS is its noise generation. High-frequency pulse-width-modulated (PWM) pulses are filtered to form the desired dc level, but the resulting ripple and radiated or conducted noise generated can negatively impact the powered equipment and nearby devices.