| 摘要 |
In connection with an automatic starting feature for an auxiliary unit, preferably a vacuum cleaner, which is switched on simultaneously when a main unit, for example an electric hand tool, a machine tool, or the like, is started it is proposed to trigger a conventional (phase) control circuit provided for the auxiliary unit by means of a current sensor taking the form of a ring-core bushing transformer in a manner such that the electric motor of the auxiliary unit is switched on with a certain delay (smooth-starting feature). The ring-core bushing transformer is designed in such a manner that, for producing clear firing pulses for the triac of the auxiliary unit, the primary winding is formed by the one turn of the electric supply line of the main unit and passed through the central opening of the ring core. The design of the ring-core bushing transformer is such that the transformer assumes the state of saturation when a predetermined output threshold value is reached so that even very high primary currents caused by the main unit during operation will not overdrive the (phase) control circuit and, in particular, not damage the triac.
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