the first switching element and the second switching element of each switching means are turned on off alternately by the pwm signals the mean potentials of the triangular signals and the sinusoidal position detection signals are set to the same potential application_number US 94490201 A description the inventive drive controller for brushless motors will now be described in detail by way of example with reference to accompanying drawings fig7 shows a structure of a drive controller for a brushless motor according to the invention fig8 shows waveforms of signals appearing at various elements of the drive controller shown in fig7 as seen in fig7 it would be recognized that the drive controller of the invention differs from the corresponding conventional drive controller shown in fig1 in that a full wave rectifier 15 nor a position detection phase shifting circuit 14 supplying polarity discrimination signals uhl vhl and whl to a pre drive circuit 17 u 17 w of fig1 is not needed it would be also recognized that the oscillator 13 the comparator 16 and the pre drive circuit 17 u 17 w of fig1 are modified in structure and hence in function in the corresponding elements shown in fig7 the modified elements are indicated by like or corresponding reference numerals with a symbol a attached thereto in fig7 other elements of fig7 including a rotor position detector 11 a torque instruction circuit 12 position detection phase shifting circuit 14 and transistor switches for three phases positive side p channel type mos transistors quh.