Drive circuit for inductive load

Claim 2

A circuit for energizing a stepping motor drive winding from a low impedance power supply comprising: a terminal means for receiving a signal indicating that the winding is to be energized; first switch means in series circuit with said winding; means connecting said first switch means to said terminal means to place said first switch means in a conductive state in response to said signal; diode means connecting said winding and said first switch means in circuit to provide a conductive path through said first switch means for the current induced in said winding upon disconnection from said power supply; second switch means connecting said winding to said power supply; current sensing means in circuit with said drive winding for developing a signal indicating current greater than a predetermined magnitude in said winding; and control means for said second switch means, means connecting said current sensing means signal to said control means to open said second switch in response to said signal; said control means for said second switch means including means for connecting said control means to said terminal means to close said second switch in response to the simultaneous existence of the signal indicating that the current in said winding is less than a predetermined magnitude.

Claim 3

A bidirectional drive circuit for a stepping motor winding comprising: a bridge circuit comprising first, second, third and fourth transistors means connecting said first and second transistors in series circuit, means connecting said third and fourth transistors in series circuit, means connecting a stepping motor winding from the junction of said first and second transistors to the junction of said third and fourth transistors, current sensing means connecting said first and third transistors to a power supply, comparator means coupled to said current sensing means for developing output signals indicating more or less than a predetermined value of current is flowing in said winding, terminal means for receiving first or second signals indicating that the winding is to be energized with current in first or second directions respectively, control means for said first transistor to place said transistor in the conductive state in response to said first signal, control means for said third transistor to place said transistor in the conductive state in response to said second signal, control means for said fourth transistor to place said transistor in the conductive state in response to the simultaneous existence of said first signal and the output signal from said comparator means indicating that less than a predetermined value of current is flowing in said winding, control means for said second transistor to place said transistor in the conductive state in response to the simultaneous existence of said second signal and the output signal from said comparator means indicating that lesS than a predetermined value of current is flowing in said winding, first and second diode means respectively connected in parallel circuit with a first circuit comprising said current sensing means, said winding and said first transistor and a second circuit comprising said current sensing means, said winding and said third transistor in a sense to oppose the flow of current from said power supply.

Claim 4

A bidirectional drive circuit for a stepping motor winding comprising: a bridge circuit comprising first, second, third and fourth transistors means connecting said first and second transistors in series circuit, means connecting said third and fourth transistors in series circuit, means connecting a stepping motor winding from the junction of said first and second transistors to the junction of said third and fourth transistors, current sensing means connecting said first and third transistors to a power supply, comparator means coupled to said current sensing means for developing output signals indicating more or less than a predetermined value of current is flowing in said winding, terminal means for receiving first or second signals indicating that the winding is to be energized with current in first or second directions respectively, control means for said first transistor to place said transistor in the conductive state in response to said first signal, control means for said third transistor to place said transistor in the conductive state in response to said second signal, control means for said fourth transistor to place said transistor in the conductive state in response to the simultaneous existence of said first signal and the output signal from said comparator means indicating that less than a predetermined value of current is flowing in said winding, control means for said second transistor to place said transistor in the conductive state in response to the simultaneous existence of said second signal and the output signal from said comparator means indicating that lesS than a predetermined value of current is flowing in said winding, first and second diode means respectively connected in parallel circuit with a first circuit comprising said current sensing means, said winding and said first transistor and a second circuit comprising said current sensing means, said winding and said third transistor in a sense to oppose the flow of current from said power supply.

Claim 5

A system according to claim 2 further including, overcurrent detection means connected to said current sensing means for developing a signal indicating excessive current flowing in said winding, current limit means connected to the overcurrent detection means and to the control means for said second and fourth transistors to limit the current passed by said second and fourth transistors in response to the signal indicating excessive current flowing in said winding.

Claim 6

A system according to claim 2 wherein, said control means for said second and fourth transistors includes a timing circuit in the control means for both said second and fourth transistors to hold said second and fourth transistors non-conductive in the state a predetermined time after the output signal from the comparator means has reappeared following an output signal indicating more than a predetermined current in said winding.