| 摘要 |
1486735 Automatic speed control PHILIPS ELECTRONIC & ASSOCIATED INDUSTRIES Ltd 23 Jan 1975 [26 Jan 1974] 2971/75 Heading G3R The speed of a D.C. motor is maintained constant by a circuit including a tachogenerator driven by the motor and producing a voltage of frequency proportional to its speed. This voltage is fed through a filter in the form of a circuit tuned to a frequency corresponding to a desired motor speed, the filter output being connected through a frequency to D.C. current converter to a control input of an amplifier which supplies the motor winding. As shown in Fig. 5, a record player turn-table motor M of shunt, series or brushless type, drives a tachogenerator T connected between the bases of transistors Tl, T2 forming a long-tailed pair and supplying a resonant filter circuit L, C, the output from which feeds a pulse shaping transistor T3 and two field effect transistors FETs, FETp forming with capacitors Cl, C2 a frequency to voltage converter. The resulting voltage signal, indicative of motor speed, passes by way of an operational amplifier circuit A to the control terminal of a supply amplifier R connected to the motor M, so as to regulate the motor speed.
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