System and method for power-efficient charging and discharging of a capacitive load from a single source

Abstract

A system and method for efficiently charging and discharging a capacitive load from a single voltage source. The system includes a first switch for selectively connecting the voltage source to the load and a second switch for selectively providing a short across the load as may be common in the art. A particularly novel aspect of the invention resides in the provision of plural capacitive elements and a switching mechanism for selectively connecting each of the capacitive elements to the load whereby the load is gradually charged or discharged. In the illustrative embodiment, the switching mechanism includes a set of switches for selectively connecting each of the capacitive elements to the capacitive load and a switch control mechanism for selectively activating the switches.

1. A system for efficiently charging and discharging a capacitive load from a single voltage source of a first potential consisting of:
 a first switch for selectively charging the load;    a second switch for selectively discharging the load;    plural capacitive elements; and    switch means for selectively connecting each of the capacitive elements to the capacitive load to gradually charge or discharge the capacitive load.    
     
     
       2. The invention of  claim 1  wherein said switch means includes plural third switches connected between said capacitive elements and said load. 
     
     
       3. The invention of  claim 2  wherein said switch means includes means for selectively activating the first, second and third switches. 
     
     
       4. The invention of  claim 3  wherein the capacitive load has a first terminal connected to the first switch and a second terminal connected to a source of a second potential. 
     
     
       5. The invention of  claim 4  wherein the second switch has a first terminal connected to the first terminal of the load and a second terminal connected to said source of a second potential. 
     
     
       6. The invention of  claim 5  wherein each of the third switches has a first terminal connected to the first terminal of the load and a second terminal connected to a first terminal of an associated one of the plural capacitive elements. 
     
     
       7. The invention of  claim 6  wherein the means for selectively activating the first, second and third switches includes a finite state machine. 
     
     
       8. The invention of  claim 7  wherein the finite state machine is designed to receive a clock signal and an input signal and provide selective activation signals for the first, second and third switches in response thereto. 
     
     
       9. The invention of  claim 8  wherein a second terminal, of each of the plural capacitive elements is connected to said source of a second potential. 
     
     
       10. The invention of  claim 9  wherein each of the capacitive elements has a capacitance which is at least an order of magnitude greater than the capacitance of the load. 
     
     
       11. A method for efficiently charging and discharging a capacitive load from a single voltage source including the steps of:
 providing a first switch for selectively connecting the voltage source to the load;    providing a second switch for selectively providing a short across the load;    providing plural capacitive elements;    providing plural third switches for selectively connecting each of the capacitive elements to the capacitive load; and    selectively activating the first, second and third switches to gradually charge or discharge the capacitive load.    
     
     
       12. A method for driving a capacitive load, comprising:
   minimizing power dissipation by discharging the capacitive load by incremental voltage steps using a switching system which includes a switch for selectively discharging the load; and        electrically coupling a capacitive storage system to the capacitive load at an electrically floating node for discharging the capacitive load by one of the incremental voltage steps.     
     
     
       13. The method of  claim 12 , further comprising: charging and discharging the capacitive load between an upper voltage and a lower voltage by the incremental voltage steps. 
     
     
       14. The method of  claim 13 , wherein one of the incremental voltage steps is the difference of the upper and lower voltages divided by an integer N. 
     
     
       15. A system for driving a capacitive load, comprising:
   means for minimizing power dissipation by discharging the capacitive load by incremental voltage steps using a switching system which includes a switch for selectively discharging the load; and means for electrically coupling a capacitive storage system to the capacitive load at an electrically floating node for discharging the capacitive load by one of the incremental voltage steps.     
     
     
       16. The system of  claim 15 , wherein the load capacitor is charged and discharged between an upper voltage and a lower voltage by the incremental voltage steps. 
     
     
       17. The system of  claim 16 , wherein one of the incremental voltage steps is the difference of the upper and lower voltages divided by an integer N. 
     
     
       18. A method for driving a load, the method comprising:
   charging the load to a first level;        discharging the load to a second level using a switching system which includes a switch for selectively discharging the load, wherein during discharging to the second level, a first capacitor is charged to the second level by using the discharging charge of the load;        discharging the load to a third level using a switch; and        re - charging the load by using the charge of the first capacitor,        wherein the first level is higher from the second level and the second level is higher that the third level.     
     
     
       19. A method of  claim 18 , wherein during discharging the load to the third level, a second capacitor is charged to the third level by using the discharging charge of the load. 
     
     
       20. A system for charging and discharging a capacitive load in N steps, N being greater than  1 , comprising:
   N− 1  capacitive devices; and        a first switching device operable to selectively couple and de - couple the N− 1  capacitive devices to and from the capacitive load during a charging and a discharging of the capacitive load;        a switching system including a switch for selectively discharging the load,        whereby energy is recovered from the capacitive load and whereby the recovered energy is always stored substantially only in capacitance.     
     
     
       21. A system of  claim 20 , wherein the first switching device is operable to selectively couple and de- couple the N− 1  capacitive devices to and from the capacitive load during both the charging and the discharging of the capacitive load.   
     
     
       22. The system of  claim 21 , wherein each of the N− 1  capacitive devices includes a capacitor. 
     
     
       23. The system of  claim 22 , wherein a capacitance of the capacitor is greater than a capacitance of the capacitive load. 
     
     
       24. The system of  claim 20 , wherein the first switching device includes a MOSFET. 
     
     
       25. The system of  claim 20 , wherein the selective coupling and de- coupling of the N− 1  capacitive devices to the capacitive load causes at least one of the charging and the discharging of the capacitive load to occur in the N steps.   
     
     
       26. The system of  claim 20 , further comprising:
   a second switching device operable to selectively couple the capacitive load to a voltage source, and        a third switching device operable to selectively provide a short across the capacitive load.     
     
     
       27. A method for charging and discharging a capacitive load comprising:
   selectively coupling and de - coupling a capacitive device to and from the capacitive load to cause the charging and the discharging of the capacitive load to occur in a plurality of steps using a switching system which includes a switch for selectively discharging the load,        whereby energy is recovered from the capacitive load and whereby the recovered energy is always stored substantially only in capacitance.