ROTATION DETECTOR FOR SMALL DC MOTOR

PURPOSE:To provide a rotation detector for small DC motors which can detect the rotation of a motor by always outputting stable detecting signals even when the current of the motor increases or decreases due to the variation of the loaded state of the motor and, at the same time, which is not restricted by the potential of each signal. CONSTITUTION:In this rotation detector which detects the rotation of a small motor 1 by obtaining detecting signals from the variation of the current IM of the motor flowing to the brush of the motor 1, the primary-side circuit of a transformer 5 is constituted of a first coil 6 to which the current IM is made to flow, second coil 7 which is connected in series with the coil 6 and, at the same time, is wound around an iron core 14 together with the coil 6 in such a state that the winding direction of the coil 7 is opposite to that of the coil 6 and the number of turns of the coil 7 is equal to that of the coil 6, and capacitor 8 connected in parallel with one of the coils 6 and 7. An AC signal S1 generated by the AC component of the current IM is outputted from the secondary-side circuit of the transformer 5.