DIN VDE 0570 | DIN EN 61558 DIN EN 61131-2
The power supply units for supplying electronic circuits are single phase or three phase with silicon bridge rectifier, decoupling capacitor, smoothing capacitor, and varistor. The direct voltage is unregulated and residual ripple < 5%. For devices with 24 V d.c. output voltage and a ripple factor of 5% the following values are laid down:
Upper limit 28,8 V | Lower limit 20,4 V
These values are adhered to, independently of mains supply fluctuation (-10% +6%).