| 摘要 |
A power supply for DC motors, in particular for actuators for use in the adjustment of tables, beds and the like, comprises a transformer (T1) with a rectifier (D1-D4) and a buffer capacitor. The power supply comprises voltage limiting means (Z1) coupled in parallel with the motor and connected to switch means (Q1) so that the motor is connected on a first part of the sine half-waves, but is disconnected when the voltage determined for the voltage limiter is reached. This ensures a good mean voltage, and the voltage does not exceed an upper permissible value. This also means that the motor speed is more independent of the load, which is an advantage e.g. in case of height-adjustable tables. In an embodiment, the power supply comprises additional means for measuring the current power in the motor, and this measurement is used as a feedback for controlling the motor speed to keep the speed of the motor. Hereby, a constant motor speed is achieved for loads up to the maximum output of the transformer, and only then begins the speed to decrease. For example in case of height-adjustable tables, the user will see under normal conditions that the tabletop is raised and lowered at a constant speed.
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