| 摘要 |
<p>1,268,516. Automatic control of speed and voltage. WARNER & SWASEY CO. Sept. 18, 1969 [Dec.9, 1968], No.46153/69. Heading G3R. A counter-EMF producing load, such as a motor or a battery being charged, is controlled by a system which samples the counter-EMF, only when the load current is less than a predetermined value. In the circuit of Fig. 2, a motor 15a is energized by a single or polyphase A. C. source 10a through antiparallel thyristors 11a, and is connected in series with a current-sensing impedance 30. When driving current is flowing in the motor, an operational amplifier 44 receives an input from the impedance 30 which is converted into a negative output to maintain a field effect transistor 54 non-conductive. However, when the motor current falls below a certain value, the effective input to the amplifier 44 becomes a negative bias voltage 50, this voltage being inverted to give a positive output which is blocked by a diode 56 to allow the transistor 54 to conduct. A capacitor 55 is now charged to a voltage proportional to the counter-EMF of the motor, and the resulting potential is compared with a reference in a feedback circuit 35, the output of which controls the firing of the thyristors 11a to regulate the motor. A time delay circuit 70 may be included in a polyphase system to delay firing of the thyristors until the capacitor 55 has had sufficient time to charge fully.</p> |
