Abstract: The invention relates to ultrasonic welding methods and apparatus for correcting the difference of frequency and phase of transducer mechanical oscillations and oscillator driving impulses to the transducer under conditions of discontinuous loading, thereby to increase the efficiency of the transducer excitation. The transducer excitation impulses are periodically supplied to the transducer at a length not more than a half-period of the transducer mechanical oscillations, and after termination are resumed again with adjustment phase and frequency determined by transducer striction feedback signals. A zero-crossing detector applies the resumed and adjusted phase and frequency driving impulses, thereby corresponding to the highest transducer sensitivity. Feedback impulses established by the transducer mechanical resonance characteristics under varying load control the phase and frequency of the excitation pulses.