Inrush current

LED control gear units provide constant direct current or buffered DC voltage for the operation of connected light sources on secondary side (see above). In both cases, the electronic connection of the control gear unit for rectification and stabilisation of the input AC voltage/AC current requires input capacitors for energy storage. The charging of the input capacitors causes a very high, short-term inrush current (see figure).

Figure 2.43: Example for an excerpt from an LED driver data sheet. This data sheet specifies the maximum inrush current caused by the driver in an electrical installation as well as notes on CB with varying magnetic trip (characteristics B and C).

The duration of a capacitor’s charging process ranges within a few μs, far shorter than the half-cycle duration of the network AC voltage. The inrush current level strongly depends on the momentary level (phasing) of the applied voltage at the time of switching and can be up to one hundred times the value of the constant current. When switching on several luminaires at once, the charging currents of the individual luminaires add up to one inrush current for a luminaire group.