Claims
- 1. An improved fuel injector drive circuit, said drive circuit having
- a switch series-connected to an inductive load, said load having first and second terminals;
- a first current recirculating branch, having nodes connected to said first and second terminals of said load, for maintaining a predetermined load voltage and enabling a fall in load current at a first predetermined rate from a peak current and having a plurality of series-connected Zener diodes;
- a second current recirculating branch parallel-connected to the load, for enabling a fall in load current at a second predetermined rate from a predetermined maximum hold current;
- a logic control unit responsive to said load current for opening and closing said switch and said branches, so that the load is supplied with current rising to said peak current, and then falling at said first predetermined rate and oscillating between said predetermined maximum hold current and a predetermined minimum hold current; the improvement comprising
- means, connected to said first branch, for varying said predetermined load voltage supplied across the load to a lower predetermined load voltage when said load current reaches a predetermined amount from said peak current, said supplied voltage varying means having a transistor having emitter and collector terminals connected to said second terminal of the load and between a predetermined pair of connected Zener diodes, a base terminal of said transistor coupled to an output of a comparator having a first input connected to a reference voltage source, and a second input connected to a load current sensing element for short-circuiting a predetermined subset of said series-connected Zener diodes;
- whereby said fall in load current from said peak current occurs at said first predetermined rate and is then slowed when said load current reaches said predetermined amount from said peak current.
- 2. A circuit for driving an inductive load, said circuit comprising
- a switch connected in series with said inductive load between first and second reference potential lines;
- a first recirculating branch having a first node connected to said first reference potential line, and a second node connected between said switch and said inductive load, and having a means for generating a predetermined bias voltage across said load to enable a fall in current through said load after said current reaches a peak value;
- a second recirculating branch connected between said switch and said first reference potential line in parallel with said inductive load, said second branch enabling a fall in current through said load;
- a logic unit for controlling said switch and said branches so that said load is supplied with current rising to said peak value, and then falling to and oscillating about a lower hold value; and
- means connected to said first branch for decreasing said bias voltage across said load when said current through said load reaches said predetermined amount less than said peak value so that said fall in current though said load is slowed after said current reaches a predetermined amount less than said peak value.
- 3. The circuit as in claim 2 wherein said first branch comprises a plurality of series-connected Zener diodes generating said predetermined bias voltage and said first branch bias voltage decreasing means comprises means for short-circuiting a subset of said Zener diodes to decrease said predetermined bias voltage.
- 4. The circuit as in claim 3 wherein said first recirculating branch comprises a transistor having a base terminal connected to said first node, an emitter terminal connected to said Zener diodes and a collector terminal connected to a third node of said first recirculating circuit, said third node connected to said second reference potential line.
- 5. The circuit as in claim 4 wherein said first recirculating branch comprises a resistive means connected between said collector terminal and said third node, said collector terminal further connected to said switch.
- 6. The circuit as in claim 3 wherein said short-circuiting means comprises a transistor having emitter and collector terminals connected between said load and said switch, and a predetermined pair of connected Zener diodes, a base terminal of said transistor connected to a second switch for turning on said transistor when said current through said load reaches said predetermined amount less than said peak value, said second switch connected to an output of a comparator having a first input connected to a reference voltage source, and a second input connected to a load current sensing element.
- 7. The circuit as in claim 6 wherein said inductive load comprises a fuel injector.
- 8. A circuit for driving an inductive load, said circuit comprising
- a switch connected in series with said inductive load between first and second reference potential lines;
- a recirculating branch having a first node connected to said first reference potential line, and a second node connected between said switch and said inductive load, said branch having a plurality of series-connected Zener diodes generating said voltage across said load to enable a fall in load current through said load after said current reaches a peak value;
- means, responsive to said load current and connected to said switch and to said first reference potential line in parallel to said load, for controlling said switch so that said load current oscillates between first and second hold values after said current falls from said peak value; and
- means, responsive to said controlling means and connected to said branch, for short-circuiting a subset of said Zener diodes to decrease said voltage across said load when said current through said load reaches a predetermined value after said current falls from said peak value;
- whereby said fall in current through said load is slowed when said current reaches said predetermined value from said peak value.
- 9. The circuit as in claim 8 wherein said recirculating branch has a third node connected to said second reference potential line and a transistor having a base terminal connected to said first node, an emitter terminal connected to said Zener diodes and a collector terminal connected to a third node of said recirculating circuit, said third node connected to said second reference potential line.
- 10. The circuit as in claim 9 wherein said recirculating branch comprises a resistive means connected between said collector terminal and said third node, said collector terminal further connected to said switch.
- 11. The circuit as in claim 8 wherein said short-circuiting means comprises a transistor having emitter and collector terminals connected between said load and said switch, and between a predetermined pair of connected Zener diodes, a base terminal of said transistor connected to a second switch for turning on said transistor when said current through said load reaches said predetermined value, said second switch connected to an output of a comparator having a first input connected to a reference voltage source, and a second input connected to a load current sensing element.
- 12. The circuit as in claim 11 wherein said inductive load comprises a fuel injector.
Priority Claims (1)
Number |
Date |
Country |
Kind |
68/037 A/90 |
Dec 1990 |
ITX |
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Parent Case Info
This is a continuation of application Ser. No. 07/810,950 filed Dec. 19, 1991, now abandoned.
US Referenced Citations (6)
Foreign Referenced Citations (3)
Number |
Date |
Country |
0288015 |
Oct 1988 |
EPX |
0319669 |
Jun 1989 |
EPX |
0290111 |
Dec 1987 |
JPX |
Continuations (1)
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Number |
Date |
Country |
Parent |
810950 |
Dec 1991 |
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