The paper is devoted to investigation of the pulse modulated systems with constant impedance load based on the application of auto-transformers in the primary circuit of pulse converters allowing to provide operation of a system with restricted range of modulated load signals and such operation conditions allow to obtain better electro-magnetic compatibility of converter with AC network without application of special filtering equipment but to respect to switches - with smaller current and voltage stresses. In the paper the main characteristics of autotransformer's circuits giving possibility to provide engineering calculations are discussed in respect to the adjustability of the constant impedance load and operation parameters of the system. Some application examples are discussed - for instance for stabilizing of AC voltage of load with the changes of supply grid voltage.