A Drive Circuit Having Voltage and Current Feedback for a Moving-Coil Actuator

Abstract

Dynamic tracking systems for video tape recorders use a moving-coil head actuator to control the head displacement with respect to the signal on the track. The head is liable to fluctuate at the mechanical resonant frequency. A voltage feedback amplifier is known to effectively reduce the Q factor of the moving-coil's resonance. However, the voltage-displacement gain depends on the coil's resistance, and that resistance is a function of temperature. On the other hand, a current feedback amplifier does not reduce the Q factor, and the gain does not vary with the coil's resistance.
In order to obtain fine tracking, both the Q factor and the gain variations need to be reduced. Consequently, a drive circuit having current feedback around the fundamental drive frequency and voltage feedback around the resonant frequency is indicated, and investigated.
The experimental results confirm that the Q factor and gain variations have both been reduced.