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Current Amplifier for Voice Coil Motor Drive

IP.com Disclosure Number: IPCOM000099973D
Original Publication Date: 1990-Mar-01
Included in the Prior Art Database: 2005-Mar-15
Document File: 2 page(s) / 52K

Publishing Venue

IBM

Related People

Enami, K: AUTHOR

Abstract

Disclosed is a current amplifier circuit for a voice coil motor drive. Many hard disk files have voice coil motors for fast traveling of magnetic heads. This current amplifier is available to get larger dynamic range of an output current.

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Current Amplifier for Voice Coil Motor Drive

       Disclosed is a current amplifier circuit for a voice coil
motor drive.  Many hard disk files have voice coil motors for fast
traveling of magnetic heads.  This current amplifier is available to
get larger dynamic range of an output current.

      A circuit shown in Fig. 1 consists of two amplifiers (Amp. 1,
Amp. 2).  These amplifiers have opposite phase outputs for one input.
 A voice coil and a resistor for detecting current are connected
between those two outputs. A voltage between both ends of the current
detecting resistor is fed back to an input of Amp 1.  Therefore, the
output current is proportional to the input voltage.

      In this circuit, a gain of Amp 2 (output voltage/input voltage)
is set larger than a gain of Amp. 1 (output voltage/input voltage) to
make Amp 2 always saturate before Amp. 1.  By setting this, the
current amplifier gets the maximum dynamic range of the output
current limited by the dynamic range of Amp. 1 and Amp. 2 output
voltage.

      In the circuit of Fig. 1, resistors R6 and R7 should be
selected as follows.
      In the case of (Vhi-Vref) > = (Vref-Vlo)
          (Vhi-Vref)/(Vref-Vlo) < = (R7/R6)
      In the case of (Vhi-Vref) < (Vref-Vlo)
           (Vhi-Vlo)/(Vhi-Vref) < (R7/R6)
Vref   ;   reference voltage of the input
*Vhi    ;   upper limit in the dynamic range of Amp. 1 and Amp. 2
*Vlo    ;   lower limit in the...