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Low distortion audio range class-AB full H-bridge pre-driver amplifier

Image Number 4 for United States Patent #6353298.

A circuit (40) and method for applying drive voltages to a voice coil motor (VCM) (22) of a mass data storage device (10) has two driver sets, each having a high side driver (HSD) (42,46) and a low side driver (LSD) (44,48) connected to the VCM (22). Each driver set has two SENSEFETs (50,52), each having a power FET and a sense FET. A circuit (106,104) is provided for sensing a sense current in the sense FET of the LSD, and a circuit (60,76,74) is provided for increasing the bias on the gates of the SENSEFET (52) in the LSD when the sense current falls below a predetermined level (VREF). Also, a circuit (113,114,110) is provided for driving a predetermined current in the SENSEFET of the HSD when the sense current falls below the predetermined level. Thus, a current at the predetermined level always flows in the SENSEFETs (50,52).

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