Drive circuit for inductive loads, particularly for fuel injectors

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.!. through said load is slowed after said current reaches a predetermined amount less than said peak value.

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.

A device for controlling an electronic fuel injector that has a solenoid and a solenoid-controlled fuel valve, said solenoid having first and second terminals, said device comprising:

• a first supply terminal coupled to said first terminal of said solenoid;
• a second supply terminal;
• a control circuit having an input terminal for receiving a fuel-injector control signal, a sensing input terminal, a first control output terminal, and a second control output terminal;
• a sensing element having a first terminal coupled to said sensing input terminal of said control circuit and having a second terminal;
• a solenoid drive switch having a control terminal coupled to said first control output terminal of said control circuit, said drive switch serially coupled to said sensing element, the series combination of said drive switch and said sensing element being coupled between said second terminal of said solenoid and said second supply terminal;
• and
• a first variable voltage controller having first and second regulator terminals respectively coupled to said first and second terminals of said solenoid, said variable voltage controller having a control terminal coupled to said second control output terminal of said control circuit.

A device for driving an inductive load, comprising:

• a drive switch coupled to said inductive load;
• a first voltage regulator coupled to said inductive load;
• and
• a control circuit coupled to said voltage regulator and to said drive switch, said control circuit being connected to receive an input signal, and in response to said input signal, said control circuit being operable to,
• close said drive switch such that a charge current flows through said inductive load,
• open said drive switch when said charge current rises to a peak level,
• control said voltage regulator to adjust the voltage across said inductive load such that a discharge current that flows through said inductive load falls at a first rate,
• detect when said discharge current falls to a first predetermined value, and
• in response to said detection, control said voltage regulator to adjust said voltage across said inductive load so as to decrease the rate at which said discharge current falls.

An inductive load drive circuit, comprising:

• 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;
• 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;
• and
• 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;
• 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.

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, said first branch providing 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 controlling said first branch so that said fall in current through said load is slowed after said current reaches a predetermined amount less than said peak value.

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 providing a 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 decreasing 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.

A method of driving an inductive load, comprising:

• causing a charge current to flow through said inductive load;
• allowing said inductive load to discharge when said charge current becomes equal to a peak value such that a discharge current that decreases at a first rate flows through said inductive load;
• causing said discharge current to decrease at a second rate when said discharge current becomes equal to a first value, said second rate less than said first rate;
• and
• causing a hold current to flow through said inductive load when said discharge current becomes equal to a second value that is less than said first value.

A method of driving an inductive load, comprising:

• coupling a first charge voltage across said inductive load such that a charge current flows through said inductive load;
• uncoupling said charge voltage from across said inductive load when said charge current attains a peak level;
• after said uncoupling, regulating a discharge voltage across said inductive load such that a discharge current flows through said inductive load, said discharge current decreasing at a first rate until said discharge current attains a first current level, said discharge current thereafter decreasing at a second rate that is less than said first rate;
• and
• when said discharge current attains a second current level, alternately coupling a second charge voltage across said inductive load and regulating said discharge voltage such that a hold current, that is between said first and second current levels flows through said inductive load.