| 摘要 |
There is provided a DC motor speed control system comprising a main motor circuit which supplies a motor current from an AC source through a full-wave rectifying circuit and a semiconductor element having a control electrode to a DC motor, a manually variable voltage setting means which is connected with the full-wave rectifying circuit, a charging circuit which is connected with the manually variable voltage setting means, a switching element having a control element which is connected with the charging circuit and, when the charged voltage in the charging circuit reaches a predetermined value, is made conductive to discharge the charging circuit thereby to supply a discharge current to the semiconductor element as a triggen current, a constant voltage element which is connected with the full-wave rectifying circuit, and a detecting means which detects the counter electromotive force induced in the motor. The constant voltage element and the detecting means are connected in series to form a series circuit the terminal voltage of which is applied to the control electrode of the switching element, and the predetermined voltage value for conduction of the switching element being variable in response to the counter electromotive force so as to delay the conduction angle of the semiconductor element for the increased counter electromotive force while to advance the conduction angle of the semiconductor element for the decreased counter electromotive force. |
