This circuit is only for the electronic commutation. The voltage in the motor coils is turned on/off depending on the position of the rotor (detected by the two hall sensors). The value of the voltage applied to the coils is controlled by VC. VC therefore controls the speed of the motor. The hall sensors are not used as on/off switches but as analog controls.
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It's a DC voltage which is varied by the EFM decoder to get the correct speed.
I did not forget.
The motor with this control is an ordinary DC motor, but with electronic commutation instead of mechanical commutation. Its speed is set by the VC voltage.
Yes, the circuit is just there to complement the hall effect sensor to replace the brushes in switching the current to appropriate coils so the motor can continuously rotating.
The brushes doesn't require electronics as it is mechanical in nature. Without the brushes (i.e. brushless motors used by expensive CD players) hall-effect sensor is commonly used to detect the position of rotor (relative to stator) so that current switching to appropriate coils can be done in time to ensure continuous rotation.
The brushes doesn't require electronics as it is mechanical in nature. Without the brushes (i.e. brushless motors used by expensive CD players) hall-effect sensor is commonly used to detect the position of rotor (relative to stator) so that current switching to appropriate coils can be done in time to ensure continuous rotation.
I have to correct my statement: It's a pulse width modulated square wave with constant frequency (e.g. 88.5kHz for the Philips CD960). At start-up of the disc, the duty cycle is typically 98% and in normal operation approx. 50%.
The motor is still an electronically commutated ("brushless") DC motor.
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