► First select the appropriate input AC voltage range (85 - 270VAC or 3x 320 - 550VAC) for your switching power supply (SMPS).
► Then buy switching power supplies with the output current that suits you, with a top-hat rail or for wall mounting, or power supplies with an extremely high protection class.
With the 28V switched mode power supply, the mains voltage is also converted into a regulated 28VDC output voltage. However, the switched mode power supply has a higher efficiency and a smaller size. After filtering and rectification, the AC input voltage is converted into a high-frequency wave-shaped pulsating voltage by a pulse-width modulated semiconductor switch and transformed into the required 28V voltage by means of a transformer on the secondary side. It is then rectified and filtered again. The power supply units of higher power are all equipped with a Power Factor Correction (PFC).