| 摘要 |
A speed control system for a motor comprises a main motor circuit for supplying the motor current to the motor from an AC power supply via a main switch, a full-wave rectifier circuit and a semiconductor element with a control electrode, variable voltage setting means connected to the full-wave rectifier circuit, charge-discharge element connected to the variable voltage setting means and impressed with a voltage set by the variable voltage setting means, and a trigger voltage supply element conducted for releasing the charges charged in the charge-discharge element to the control electrode of the semiconductor element as a trigger voltage when the charge voltage of the charge-discharge element reaches a predetermined level. The speed control system further comprises means for detecting the electromotive force of the motor and automatically variable resistance means connected to the charge-discharge element and having its resistance value automatically varied in response to the electromotive force of the motor detected by the motor electromotive force detector means. The automatically variable resistance means controls the charging current to the charge-discharge element in accordance with the resistance value thereof. The conduction phase of the semiconductor element is retarded with an increase in motor electromotive force and advanced with a decrease in motor electromotiveforce.
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