R.I. Zudov - Post-graduate Student, St. Petersburg State Polytechnical University. E-mail: ronnwind@gmail.com
V.A. Sorotsky - Dr. Sc. (Eng.), Head of Department, St. Petersburg State Polytechnical University. E-mail: sorotsky@mail.spbstu.ru

Class DE amplifiers are widely used in radio engineering applications due to its high efficiency originating from rather low switching losses in semiconductor devices. Unlike many known publications devoted to the amplifiers of that type in which the consideration of processes is usually restricted by the case of fixed frequency operation of a device, the paper focuses on the study of characteristics of an amplifier operating in the frequency band. The results will contribute to the use of switch-mode class DE amplifiers in radio transmitters and provide conditions to significantly improve their efficiency. Taking into consideration that switching losses in semiconductor devices can be reduced to zero only under certain conditions which depend upon both: the circuit parameters and frequency, ensuring high efficiency of an amplifier operating in the frequency band is not a trivial task. The aim of the paper is to determine the requirements to the power amplifier-s load features proceeding from the acceptable efficiency decline. The characteristics of the real and imaginary parts of the load impedance necessary to provide amplifier-s high efficiency are calculated using the harmonic balance method. They can be used for the synthesis of radio transmitters - output filtering and matching circuits.