International Business Machines Corporation

Walter H Sakmann

Volker W Zimmermann

Albrecht Lang

A pulse-operated transistor power amplifier having reduced switching times. The interconnected base electrodes of a pair of complementary transistors (T3, T4) are connected to the collector of a prestage transistor (T1). By a resistor (R2), the base electrodes are also connected to one terminal (+V) of the operating voltage source, to which the collector of one (T4) of the two complementary transistors is also connected. The collector of the other transistor (T3) is connected to the other terminal of the operating voltage source, which is linked with the reference potential. The emitters of the complementary transistors are also connected to each other and, by a capacitor (C1), to the base of the final stage. The voltage changes occurring at the collector when the prestage is switched are transferred by one of the two complementary transistors and the capacitor (C1) to the base of the final stage transistor (T5). The switching times of this stage are reduced by base charges which are additionally supplied or withdrawn. In a further embodiment a transistor power amplifier having two series-connected complementary final stages (T 5, T6) simultaneous conduction of both final stage transistors is prevented by means of a capacitor (C3), one electrode of which is connected to the interconnected emitters of the additional complementary emitter follower for the final stage (T6) switching the reference potential, and the other electrode of which (C3) is connected by a diode (D4) to the base of the complementary final stage (T5). The two inputs (R, U) of the power amplifier are also provided with protection transistors (T10, T11) which when one input transistor (T1) becomes conductive prevent the second input transistor (T2) from becoming conductive as a result of an erroneous input signal.

Transistor power amplifier having reduced switching times

Method and apparatus for the constant speed control of a brushless DC motor, whose pole windings receive a pulsed control voltage between their commutation points, control being a function of the speed characteristics of the motor, and the commutation points being synchronized with the drop times of the motor current and the control voltage pulses. In a state in which there are no load changes, the motor current substantially rises or drops between a maximum value I.sub.max and a minimum value I.sub.min according to the pulse mode. In the event of changes in the motor load, a mean motor sum current is retained for maintaining the speed.

Method and apparatus for the constant speed control of brushless DC

A type band for a steel band printer containing a track of sensible timing marks is provided with two additional sensible marks each located between two timing marks. The printer counts the number of sensible timing marks occurring between the two additional marks to identify the character set on the type band.

Type band and band printer with automatic print band recognition

A matrix printer with piezoelectrically driven printing needles is described in which an electrically controlled piezocrystal arrangement transfers upon its expansion, its change of length to a buckling spring. Coupled to the buckling compression column spring is a printing needle which, upon the deflection of the buckling spring, is driven in the printing direction.

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Nufringen, Germany

Walter H Sakmann