Driver circuit for piezoelectric element, having voltage limiter capable of charging the element with energy from coil after charging switch is off

Claim 2

A driver circuit for driving a piezoelectric element having a capacitance C, including a DC power source, and a coil having an inductance L and connected in series with said piezoelectric element and said power source, said piezoelectric element being alternately charged and discharged while oscillating with said coil at a predetermined frequency, said driver circuit comprising: first conditioning means for charging said piezoelectric element, said first conditioning means being normally placed in an original state for inhibiting said piezoelectric element from being charged, and brought to a charging state for allowing said piezoelectric element to be charged, in response to a drive command to activate said piezoelectric element, said first conditioning means being held in said charging state for a time period not shorter than (π√LC)/3, and returned to said original state at a first point of time before a voltage of said piezoelectric element has reached a predetermined level not higher than a line voltage of said power source; voltage limiting means for allowing said piezoelectric element to be charged with an energy stored in said coil after said piezoelectric element has been charged by said first conditioning means, and preventing said piezoelectric element from receiving an excessive energy that causes said voltage of the piezoelectric element to exceed said predetermined level; and second conditioning means for discharging said piezoelectric element, said second conditioning means being normally placed in an original state for inhibiting said piezoelectric element from being discharged, and brought to a discharging state for allowing said piezoelectric element to be discharged, at a second point of time not earlier than said first point of time, said second conditioning means being returned to said original state thereof by the time when said first conditioning means is placed in said charging state thereof for a next activation of said piezoelectric element.

Claim 3

A driver circuit according to claim 1, wherein said first conditioning means comprises time measuring means for measuring a time period after said first conditioning means is brought to said charging state, and returning said first conditioning means to said original state when the time period measured by said first time measuring means has reached a first reference time period which defines said first point of time.

Claim 4

A driver circuit according to claim 1, wherein said second conditioning means comprises time measuring means for measuring a second time period after said first conditioning means is brought to said charging state, and returning said second conditioning means to said original state when the time period measured by said time measuring means has reached a second reference time period which defines said second point of time.

Claim 5

A driver circuit according to claim 1, wherein the drive circuit includes a charging circuit incorporating a series connection of said DC power source, said coil and said piezoelectric element, and a discharging circuit having a closed path which includes said piezoelectric element and excludes said DC power source.

Claim 6

A driver circuit for driving a piezoelectric element having a capacitance C, including a DC power source, and a coil having an inductance L and connected in series with said piezoelectric element and said power source, said piezoelectric element being alternately charged and discharged while oscillating with said coil at a predetermined frequency, said driver circuit comprising a charging circuit incorporating a series connection of said DC power, said coil and said piezoelectric element, and a discharging circuit having a closed path which includes said piezoelectric element and excludes said DC power source, said driver circuit comprising: first conditioning means for charging said piezoelectric element, said first conditioning means comprising first switching means connected in series with and between said coil and a positive terminal of said DC power source of said charging circuit, and first switching means for normally placing said first switching means in an original state for inhibiting said piezoelectric element from being charged, and for bringing said first switching means to a charging state for allowing said piezoelectric element to be charged, in response to a drive command to activate said piezoelectric element, said first switching means holding said first switching means in said charging state for a time period not shorter than (π√LC)/3, and returning said first switching means to said original state at a first point of time before a voltage of said piezoelectric element has reached a predetermined level not higher than a line voltage of said DC power source; voltage limiting means for allowing said piezoelectric element to be charged with an energy stored in said coil after said piezoelectric element has been charged by said first switching means, and preventing said piezoelectric element from receiving an excessive energy that causes said voltage of the piezoelectric element to exceed said predetermined level, said voltage limiting means comprising a closed by-pass circuit which by-passes said first switching means and which includes said DC power source, said coil, and first checking means connected in series to said power source and said coil, said checking means allowing a flow of an electric current in a direction from said coil toward said positive terminal of said power source, and inhibiting a flow of electric current in a direction from said positive terminal of said power source toward said coil; and second conditioning means for discharging said piezoelectric element, said second conditioning means comprising second switching means provided in said discharging circuit such that said second switching means is connected in series with said piezoelectric element, and further comprising second switching control means for normally placing said second switching means in an original state for inhibiting said piezoelectric element from being discharged, and bringing said second switching means to a discharging state for allowing said piezoelectric element to be discharged, at a second point of time not earlier than said first point of time, said second switching control means returning said second switching means to said original state by the time when said first switching means is placed in said charging state for a next activation of said piezoelectric element.

Claim 7

A driver circuit for driving a piezoelectric element having a capacitance C, including a DC power source, and a coil having an inductance L and connected in series with said piezoelectric element and said power source, said piezoelectric element being alternately charged and discharged while oscillating with said coil at a predetermined frequency, said driver circuit comprising a charging circuit incorporating a series connection of said DC power, said coil and said piezoelectric element, and a discharging circuit having a closed path which includes said piezoelectric element and excludes said DC power source, said driver circuit comprising: first conditioning means for charging said piezoelectric element, said first conditioning means comprising first switching means connected in series with and between said coil and a positive terminal of said DC power source of said charging circuit, and first switching means for normally placing said first switching means in an original state for inhibiting said piezoelectric element from being charged, and for bringing said first switching means to a charging state for allowing said piezoelectric element to be charged, in response to a drive command to activate said piezoelectric element, said first switching means holding said first switching means in said charging state for a time period not shorter than (π√LC)/3, and returning said first switching means to said original state at a first point of time before a voltage of said piezoelectric element has reached a predetermined level not higher than a line voltage of said DC power source; voltage limiting means for allowing said piezoelectric element to be charged with an energy stored in said coil after said piezoelectric element has been charged by said first switching means, and preventing said piezoelectric element from receiving an excessive energy that causes said voltage of the piezoelectric element to exceed said predetermined level, said voltage limiting means comprising a closed by-pass circuit which by-passes said first switching means and which includes said DC power source, said coil, and first checking means connected in series to said power source and said coil, said checking means allowing a flow of an electric current in a direction from said coil toward said positive terminal of said power source, and inhibiting a flow of electric current in a direction from said positive terminal of said power source toward said coil; and second conditioning means for discharging said piezoelectric element, said second conditioning means comprising second switching means provided in said discharging circuit such that said second switching means is connected in series with said piezoelectric element, and further comprising second switching control means for normally placing said second switching means in an original state for inhibiting said piezoelectric element from being discharged, and bringing said second switching means to a discharging state for allowing said piezoelectric element to be discharged, at a second point of time not earlier than said first point of time, said second switching control means returning said second switching means to said original state by the time when said first switching means is placed in said charging state for a next activation of said piezoelectric element.

Claim 8

A driver circuit according to claim 5, further comprising third switching means connected in parallel with a series connection of said first switching means and said coil, and third switching control means for turning on said third switching means at a third point of time not earlier than a moment of completion of charging of said piezoelectric element by said voltage limiting means.

Claim 9

A driver circuit according to claim 5, wherein said discharging circuit includes said coil in series connection with said piezoelectric element, said driver circuit further comprising: second checking means which is connected in parallel with said first switching means and which allows a flow of an electric current in a direction from said coil toward said positive terminal of said power source and inhibiting a flow of the electric current in a direction from said positive terminal of said power source toward said coil; and third checking means which is connected in series with and between a negative terminal of said power source and an end of said coil connected to said piezoelectric element and which allows a flow of an electric current in a direction from said negative terminal of said power source toward said end of said coil and inhibits a flow of the current in a direction from said end of said coil toward said negative terminal of said power source; said coil, said power source, said second checking means and said third checking means constituting a closed energy returning circuit for returning an energy stored in said coil to said power source after said second switching means is turned off.

Claim 10

A driver circuit according to claim 5, wherein said first switching means and said second switching means comprise a first and a second transistor, respectively, and said first switching control means and said second switching control means are constituted by a computer.

Claim 11

A driver circuit according to claim 5, wherein said first checking means comprises a diode connected in series with and between a negative terminal of said DC power source and said coil, and another diode connected in series with and between said coil and said positive terminal of said power source.