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Voice Coil Driver

IP.com Disclosure Number: IPCOM000035049D
Original Publication Date: 1989-May-01
Included in the Prior Art Database: 2005-Jan-28
Document File: 2 page(s) / 70K

Publishing Venue

IBM

Related People

Ell, TE: AUTHOR

Abstract

The linear voice coil driver is capable of driving inductive voice coil loads with acceptable time domain responses. As shown in Fig. 1, the voice coil driver is composed of five stages. The stages are a compensation stage, an inverting power op amp stage, a noninverting power op amp stage, a transimpedance stage, and a power shut down/retract stage. The basic building blocks for the power op amp stages are an externally compensated op amp and a lag type power booster stage. The op amps 3 and 4 are used because they can be externally compensated using capacitors C341 and C342. The bandwidth of the op amps are reduced (Image Omitted) because the bandwidth limitations of the power transistors would cause the circuit to be unstable.

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Voice Coil Driver

The linear voice coil driver is capable of driving inductive voice coil loads with acceptable time domain responses. As shown in Fig. 1, the voice coil driver is composed of five stages. The stages are a compensation stage, an inverting power op amp stage, a noninverting power op amp stage, a transimpedance stage, and a power shut down/retract stage. The basic building blocks for the power op amp stages are an externally compensated op amp and a lag type power booster stage. The op amps 3 and 4 are used because they can be externally compensated using capacitors C341 and C342. The bandwidth of the op amps are reduced

(Image Omitted)

because the bandwidth limitations of the power transistors would cause the circuit to be unstable. Q327, Q328, Q329, and Q330 form a level translation stage to the power transistors Q320, Q321, Q322, and Q323. Capacitors C343 and C346 set the pole-zero location for the lag network. The gain of the power booster stage at "high frequencies" is one until the cutoff frequencies of the power transistors are reached. The closed loop gains for the power op amp stages are set at 1.5 and -1.5 by resistors R462, R464, R468, and R481. The transimpedance stage senses the current in the coil via the voltage across a 0.5 ohm resistor R475. This voltage is amplified by a gain of two by an op amp and resistors R476, R478, R477, and R479.

The overall gain for this stage is 1 volt/amp. The compensation stage is used to cancel the pole...