Constant-frequency current choppers for low-rate supply of an inductive load

Claim 1

In a constant-frequency current chopper connected between a voltage source and a load for low-rate supply of such load and comprising: a main thyristor, shunted by a cutoff circuit including therein a cutoff thyristor in series connection with a cutoff capacitor in a resonating discharge circuit having a first thyristor, and a control circuit means for controlling conductivity of said main, cutoff and first thyristors, each thyristor herein or hereafter recited having anode, cathode and gate terminals, said chopper being connected between a first terminal of said voltage source and said load, the improvement comprising: a. additional discharge means for discharging said cutoff capacitor, said additional discharge means being connected across said cutoff capacitor, and b. decoupling means connected between said chopper and a second terminal of said voltage source for preventing excessively rapid variation of voltages applied to said thyristors, c. wherein said control circuit means provides low current values to said load by providing for conductivity of said cutoff thyristor during a time when said additional discharge means is discharging said cutoff capacitor, d. wherein said control circuit means provides increased current to said load by providing for said conductivity of said cutoff thyristor at earlier times during said discharge of said cutoff capacitor by said additional discharge means, and e. wherein said control circuit means provides larger current values to said load by providing for conductivity of said main thyristor prior to providing for conductivity of said cutoff thyristor.

Claim 11

A method for controlling current delivered by a constant frequency current chopper to an inductive load comprising the steps of: a. causing a thyristor in a resonating discharge circuit for a cutoff capacitor to enter a conductive state at a first point in time; b. causing a diode in an additional discharge circuit across said cutoff capacitor to enter a conductive state at a second, subsequent point in time when the voltage across said cutoff capacitor has changed by a predetermined amount; c. causing said thyristor in said resonating discharge circuit to terminate its conducting state at a still subsequent, third point in time; d. causing said diode in said additional discharge circuit to terminate conductance at a still further, fourth point in time, and e. obtaining low current for said load by causing a cutoff thyristor to turn on at a point in time between said second and said fourth points in time when said diode in said additional discharge circuit is in its conducting state, f. decreasing said low current supplied to said motor by causing said cutoff thyristor to turn on at a point approaching said fourth point in time.

Claim 12

A method for controlling current delivered by a constant frequency current chopper to an inductive load comprising the steps of: a. causing a thyristor in a resonating discharge circuit for a cutoff capacitor to enter a conductive state at a first point in time; b. causing a diode in an additional discharge circuit across said cutoff capacitor to enter a conductive state at a second, subsequent point in time when the voltage across said cutoff capacitor has changed by a predetermined amount; c. causing said thyristor in said resonating discharge circuit to terminate its conducting state at a still subsequent, third point in time; d. causing said diode in said additional discharge circuit to terminate conductance at a still further, fourth point in time, and e. obtaining low current for said load by causing a cutoff thyristor to turn on at a point in time between said second and said fourth points in time when said diode in said additional discharge circuit is in its conducting state, f. decreasing said low current supplied to said motor by causing said cutoff thyristor to turn on at a point approaching said fourth point in time.