| 摘要 |
<p>A tape tension control system for a video tape recorder in which a first motor is coupled to a supply reel, a second motor is coupled to a takeup reel and a capstan is provided for driving the tape between supply and takeup reels in a normal running mode. Tachometers are associated with each reel and with the capstan. Signal processing circuits are provided for indirectly sensing diameters of tape on the respective reels. The required torque of each motor is determined by comparing the signals representing tape diameter with a reference sawtooth waveform. The sawtooth waveform is provided across a first capacitor coupled via a first transistor switching means to a source of charging current. A second capacitor is coupled to the current source for biasing the transistor into conduction after a predetermined time delay. A biasing supply is coupled to the alternating voltage source for varying the time delay in response to variations in the alternating voltage. Further switching means are coupled to the first and second capacitors for periodically discharging the capacitors in synchronism with the alternating voltage.</p> |
