Rated power of second additional switching device 9 can be decreased more in a technical solution (FIG. 37) where the steps of switching on of second additional switching devices 9 is controlled by zero crossing (voltage) control device 13 connected to said voltage source 1 through a bridge rectifier 14. Rated power of said additional switching device 7 can be decreased more in the technical solutions (FIG. 35 and FIG. 36) where the steps of switching on of said additional switching devices 7 is controlled by zero crossing (voltage) control device 13 connected to said voltage source 1 through a bridge rectifier 14. Known zero crossing (voltage) control are used opto-coupler for triggering control circuit of a TRIAC. For switching on said additional switching device 7 (FIG. 35 and FIG. 36) or said second additional switching device 9 (FIG. 37) can be used control system which is similar to control systems, described in U.S. Pat. No. 6,320,281 of the applicant, for example, presented in FIG. 9, FIG. 10, FIG. 11 and FIG. 20 of said patent. As an additional switching device 7 or an second additional switching device 9 can be also used a TRIAC.