Abstract: A braking system for an electrical stepping motor having its rotor mechanically connected to drive a transducer carriage of a magnetic disk drive machine, the braking system including a transistor which is responsive to the voltage across the stator coils of the stepping motor and initiates the controlled discharging of a capacitor. The charge on the capacitor is effective through transistor control circuits so as to short all of the stator coils, with the exception of the one to which an energizing voltage is applied for locating the rotor in its target position, when the capacitor discharges in a predetermined time so as to brake the rotor as the rotor approaches its target position on a return movement after the rotor initially passes across its target position.

Abstract: Small current signals (0.5 ua and less) such as the output of a photodiode are direct current coupled to a preamplifier which also passes an impedance reducing injection current to a pair of amplifiers. A voltage output proportional to the logarithm of the signal current is produced by passing the amplified current through a log producing junction of a transistor. However, to produce the logarithm function accurately, the injected or impedance reducing current is precisionally removed so that only a very minute portion (one part out of 5000) passes through the log producing junction.