Chopper circuit for use in an a.c. servo amplifier

Claim 2

A control circuit for driving a servomotor comprising: a chopper circuit providing regularly reoccurring square wave voltage pulses of constant frequency and selectable voltage level, said square wave voltage pulses including spike voltage signals imposed thereon; time complement spike signal generating circuit means providing a spike voltage signal of equivalent amplitude and of opposite phase: means summing said chopper circuit square wave voltage pulses and said time complement spike voltage signal to provide a chopper square wave voltage signal output of variable amplitude and substantially free of spike components; an amplifier having an input and an output, the input being connected to said summing means for amplifying the output of said chopper circuit summing means; a motor drive circuit having an input and an output, the input being connected to said amplifier output and the output being connectable to a servomotor; wherein said chopper circuit includes a transistor having a gate electrode and having a drain and a source electrode in series with a load resistor and a DC voltage source; and wherein said time complement spike signal generating means includes a first and second square wave generating transistor connected in paralleled differential arrangement and including a single emitter follower resistor, the base of said second transistor being connected to a fixed voltage potential and the base of the first transistor being connected to a square wave signal source, the output of the first transistor being connected to drive said chopper circuit, and the output of the second transistor being connected to the output of said chopper circuit wherein the outputs of said chopper circuit and said second transistor are summated.

Claim 3

A chopper circuit for driving a servomotor according to claim 1 wherein said chopper circuit and said summing means comprises: a field effect transistor having a drain electrode, a source electrode, and a gate electrode; a DC voltage source connected between said drain and source electrodes; a load resistor in series with and between said DC voltage source and one of said drain and source electrodes; circuit means imposing a driving square wave voltage signal on said gate electrode, said square wave voltage signal serving to alternately cause said transistor to conduct and cut off, the output of the chopper circuit being taken between said load resistor and said drain electrode; circuit means imposing a spike canceling square wave voltage signal on the one of said drain and source electrodes connected to said load resistor, the spike canceling square wave voltage signal being a time complement of said driving square wave voltage signal; wherein said circuit means imposing said driving signal and said spike canceling signal comprises: a first and a second paralleled square wave generating transistor each having a collecTor electrode, an emitter electrode, and a base electrode; paralleled emitter follower resistors, there being one in series with the emitter electrode of each of said square wave generating transistors, the paralled emitter follower resistors being connected to a first circuit common point; a series emitter follower resistor between said circuit common point and ground; paralleled collector load resistors, there being one in series with the collector electrode of each of said square wave generating transistors, the paralleled collector load resistors each being connected to a second circuit common point; a voltage source connected between ground and said second circuit common point; means imparting a square wave signal on said base electrode of said first square wave generating the base electrode of said second square wave generating transistors being connected to a DC voltage potential, said driving signal being taken between said collector electrode of said first transistor and said collector load resistor in series therewith, and said spike canceling signal being taken between said collector electrode of said second transistor and said collector load resistor in series therewith.

Claim 4

A chopper circuit for driving a servomotor according to claim 2 wherein said means imparting a square wave signal on said first square wave generating transistor base electrode includes: a signal generating transistor having a collector electrode, a grounded emitter electrode, and a base electrode; a diode connected between ground and said signal generating transistor base electrode and ground; a resistor between said signal generating transistor base electrode and an alternating sine wave signal source; and a first and second seriesed load resistor between said signal generating transistor collector and a DC voltage source, said base of said first square wave generating transistor being connected between the first and second seriesed load resistors.