by the signal 21 and previously indicated in fig1 and 2 as 19 is made up of a triac in this way when the signal 21 is high this triac 19 comes into operation and the motor is supplied with full power when the signal 21 is low however the triac 19 is cut off and the motor is supplied with a partial wave as described above it will be clear to a technician how the divider r6 r7 acts as the reference generator illustrated by 24 in fig1 in fact the reference voltage at point 36 provides a threshold for the operation of the dual state control circuit 10 39 if the current absorbed by the motor is lower than a certain value which is best selected barely higher than the no load current of the motor the voltage at point 30 will be higher than the threshold in this way the motor when it is load free is supplied with partial power thus preventing overspeed if the current absorbed by the motor is higher than the aforementioned certain value the voltage at point 30 will be higher than the threshold so that the motor is supplied with full power in this way as soon as the motor is loaded and there is therefore no risk of overspeed the motor is supplied with its normal operating power a further.