Abstract:
The present invention is a power conditioning circuit. The invention is comprised of multiple comparators and a bilateral switch. The invention converts the high-frequency, high-voltage output signal from a piezoelectric transformer to a desired low-frequency voltage signal, examples including but not limited to sinusoidal, sawtooth, ramp, and square waves, at the output amplitude voltage. The circuit switches the high-frequency AC output, also referred to as the driving waveform, into the load at precisely the instant when the driving waveform crosses the present voltage load value, and switches it out when the load waveform reaches the desired voltage. Thereafter, the switch is opened and the reactance of the load or an additional output capacitor element holds the voltage until the next switching cycle.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The application claims benefit under 35 U.S.C. 119(e) from U.S. Provisional Application No. 60/268,096 filed on Feb. 12, 2001. 
     FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     None. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention generally relates to a circuit capable of driving electrical loads. The invention specifically described is a circuit that develops a commanded DC or AC signal from the high-frequency AC output voltage of a piezoelectric transformer. 
     2. Related Arts 
     A conventional power distribution circuit, as shown in FIG. 1 a , steps-up and steps-down AC voltage via an electromagnetic transformer wherein primary and secondary windings are electromagnetically coupled to a magnetic core. Both windings and magnetic core limit miniaturization of such devices. 
     A conventional piezotransformer-based distribution circuit, as shown in FIG. 1 b , also provides for voltage step-up and step-down. More specifically, a Rosen transformer excites a piezoelectric element at resonance frequency with an electrical input at one end of the element generating a mechanical vibration, thereafter converting mechanical vibrations into electrical voltage at a second end of the element. Piezoelectric transformers are smaller, lighter, and more efficient than conventional electromagnetic devices, however constrained to a limited operating frequency below that of electromagnetic transformers. 
     Higher frequency piezoelectric transformers are possible. Such devices achieve both higher operating frequency and higher power density than conventional Rosen transformers via a thickness extensional vibration mode. The resultant device operates at multiple voltage levels, since output voltage is dependent on the thickness ratio between individual layers along first and second ends of the piezoelectric element. 
     The output from a piezoelectric transformer has parallel capacitance and a capacitive load. Therefore, neither output nor load are directly switchable into the other except with an intervening element, typically an inductor to maintain efficiency. The related arts transform the high-frequency output from a piezoelectric transformer to DC voltage via a bridge rectifier and a fairly large capacitor. DC voltage is applied as a power supply for a switching amplifier to drive the load, again requiring a filter inductor, an inverter circuit and a feedback circuit. 
     Much of the complexity, bulk, and weight in the related arts is avoided by switching the high-frequency AC output from the piezoelectric transformer, also called the driving waveform, into the load at precisely the instant when the driving waveform crosses the present voltage value on the load and switching the load out when the driving waveform reaches the desired voltage. Thereafter, the switch is opened and the reactance of the load or an addition output capacitor element holds the voltage until the next switching cycle. A single bilateral switch is required. 
     An object of the present invention is to provide a smaller, lighter, and less complex circuit capable of driving electrical loads. A further object of the present invention is to provide a circuit capable of developing an AC voltage signal input from the high-frequency AC output of a piezoelectric transformer without capacitors or inverter. 
     SUMMARY OF THE INVENTION 
     The present invention is a drive circuit functionally distinct from conventional linear and switching drives and representing a new device called a trasversion or transconverter device. The invention is comprised of several high-frequency comparators and at least one bilateral switch. The invention converts one or more high-frequency output voltage signals from a piezoelectric transformer to low-frequency voltage signals, examples including but not limited to sinusoidal, sawtooth, ramp, and square waves, at the output amplitude voltage. The circuit switches a high-frequency AC voltage output from a piezoelectric transformer, also referred to as the driving waveform, into the load at precisely the instant when the driving waveform crosses the present voltage value on the load, and switches it out when the driving waveform reaches the desired voltage. Thereafter, the switch is opened and the reactance of the load or an additional output capacitor element holds the voltage until the next switching cycle. The circuit functions without inverter and regulation sections required in the related arts. 
     The circuit is applicable to various piezoelectric transformer sections wherein a high-voltage AC signal and a low-level supply are separately provided. For example, the present invention is applicable to a conventional piezoelectric transformer, a piezoelectric transformer coupling with high-level and low-level “winding” outputs, and a dual piezoelectric transformer. 
     Several advantages are offered by the present invention. The invention is smaller, lighter, less costly, and more reliable than the related arts due to the elimination of iron core/ferrite transformer and amplifier. The invention eliminates large capacitors and invert section in the related arts. The invention is a modular design readily adaptable to a wide range of current-voltage output characteristics and waveforms. The invention generates an extremely low EMI/RFI signature and has a wide thermal excursion operating capability. The invention is widely applicable in such items as flourescent lighting systems, backlit lighting systems, computer electronics, and active materials and devices. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will now be described in more detail, by way of example only, with reference to the accompanying drawings, in which: 
     FIG. 1 describes power distribution schemes found in the related arts. 
     FIG. 2 is a schematic diagram showing present invention with piezoelectric transformer. 
     FIG. 3 is a block diagram showing signal conditioning circuit coupled to input and output elements. 
     FIG. 4 is a functional description of the present invention. 
     FIG. 5 is a circuit diagram showing preferred embodiment comprised of four analog comparators and a MOSFET switch. 
     FIG. 6 illustrates transconversion of high-frequency AC voltage signal from a piezoelectric transformer to desired voltage signal at an electrical load. 
     FIG. 7 illustrates transconversion of high-frequency DC voltage signal from a piezoelectric transformer to desired voltage signal at an electrical load. 
     FIG. 8 is a voltage-time plot for output waveform from preferred embodiment. 
     FIG. 9 is an enlarged view of voltage-time plot showing stepwise waveform. 
     FIG. 10 is diagram showing a plurality of circuits arranged forming a single power distribution system. 
    
    
     NUMERICAL REFERENCE 
       1  Power source 
       2  Piezoelectric transformer 
       3  Drive circuit 
       4  Input side 
       5  Output side 
       6  High-frequency signal 
       7  Reference waveform 
       8  Output signal 
       10  Comparator circuit 
       12  Power distribution system 
       20  Power supply 
       21  Bulk converter 
       22  power storage element 
       23  dedicated element 
       24  Output side connection 
       25  AC generator 
       26  piezotransformer 
       27  Drive circuit 
       28  Supply power waveform 
       29  High-frequency signal 
       30  Output signal 
       50  Crossover point 
       51  Leading edge segment 
       52  Trailing edge segment 
       53  Desired voltage waveform 
       54  High-frequency AC signal 
       61  Reference voltage 
       62  Actual voltage 
       63  Actual voltage 
       64  Crossover point 
       65  Trailing edge segment 
       67  Desire voltage waveform 
       68  High-frequency DC signal 
       69  Actual voltage 
     X 1  Comparator 
     X 2  Comparator 
     X 3  Comparator 
     X 4  Comparator 
     L 1  Load 
     S 1  Switch 
     S 2  Switch 
     DESCRIPTION OF THE INVENTION 
     The present invention facilitates AC rectification, as well as DC rectification of AC or DC power. The described invention is quite distinct from the related arts where rectification is provided on the output side only. Multiple transconverters supply both separate AC voltage signals and DC voltage signals using the same level-shifting piezoelectric transformer. Elimination of traditional passive filter components allows manufacture of the transconversion device as a foundry solid state component. 
     FIG. 3 shows the present invention, namely a drive circuit  3 , electrically coupled at an input side  4  to a power source  1  and a piezoelectric transformer  2 , and at an output side  5  to one or more loads L 1 . The power source  1  energizes a piezoelectric transformer  2  with a high-frequency, low voltage at one end thereby producing a high-frequency signal  6  with stepped-up voltage at the other end. A very-high-frequency chopper device conditions power from the power source  1 . Power supplies and chopper devices comprising the power source  1  are readily understood by one in the art. Thereafter, the high-frequency signal  6  with stepped-up voltage is communicated to the drive circuit  3  where it is modified and electrically communicated to one or more loads L 1  at the output side  5 . Loads L 1  include electrical devices as understood in the art, examples including capacitive and transductive elements. 
     Conventional piezoelectric transformers  2  such as the TRANSONER® are manufactured by Face International Corporation of Norfolk, Va. The self-contained implementation of the invention requires either a multi-tap piezoelectric transformer  2  or two separate piezoelectric transformers  2 . FIG. 2 provides a block diagram for the present invention coupled to a multi-tap piezoelectric transformer  2 . 
     FIG. 4 graphically describes functionality of the drive circuit  3 . In this example, the drive circuit  3  is comprised of a comparator circuit  10  composed of a plurality of comparators electrically arranged and connected and thereafter electrically connected about a bidirectional switch S 1 . The comparator circuit  10  is comprised of signed components thereby facilitating both stepwise increase and decrease of voltage into the load L 1 . The comparator circuit  10  is electrically connected to a switch S 1  regulating current flow from the piezoelectric transformer  2  to the load L 1 . An optional second switch S 2  is provided to dump charge from the load L 1 . Dual switch S 1 , S 2  embodiments are driven in opposite phase and charge direction relative to the load L 1 . 
     Drive circuit  3  generates an output signal  8  having the form of a reference waveform  7  by selectively passing portions of the high-frequency signal  6  from the piezoelectric transformer  2  to the load L 1 . The comparator circuit  10  receives voltage data about the switch S 1  and compares this to the reference waveform  7 . The comparator circuit  10  OPENS and CLOSES the switch S 1 , referred to as the condition, thereby passing only that portion of the high-frequency signal  6  required to increase or decrease voltage as desired in the output signal  8 . 
     FIG. 5 shows a four comparator X 1 , X 2 , X 3 , X 4  embodiment of the drive circuit  3 . Switch S 1  condition is controlled by a standard TTL or CMOS circuit with comparator X 1 , X 2 , X 3 , X 4  outputs, namely VA, VB, VC, and VD as inputs, and the switch S 1  drive signal as output. Switch S 1  condition is determined from four parameters. First, whether the next voltage along the output signal  8 , for example gain times reference signal  7 , is higher or lower than the present voltage along the output signal  8 . Second, whether the high-frequency signal  6  crosses the next voltage. Third, whether the high-frequency signal  6  crosses the present voltage. Fourth, whether the high-frequency signal  6  is increasing or decreasing. 
     High-speed sampling by the comparators X 1 , X 2 , X 3 , X 4  is required to identify all four conditions. The first three parameters are determined using the corresponding voltages as inputs to the comparators X 1 , X 2 , X 3 . In practice, the desired output voltage is determined by the input voltage, and the high-frequency signal  6  and the present voltage are divided down to the same level. Voltage dividers determine the voltage gain of the amplifier, while the maximum output of the high-frequency signal  6  determines amplitude. The fourth parameter is determined by passing the high-frequency signal  6  through an attenuating differentiator, preferable filtering high-frequency noise, where the resulting waveform and zero are inputs to a fourth comparator X 4 . Table 1 summarizes representative values for components in FIG.  5 . 
     Multi-tap piezoelectric transformer  2  embodiments include an AC signal as an input and a plurality of AC voltages as output. In preferred embodiments, a filter capacitor is provided at the output side  5  to maintain voltage between opening and closing of the switch S 1 . Drive circuit  3  components as well as single or dual MOSFET type switches S 1 , S 2  are readily integratable at the foundry level. A wide range of voltage outputs are achievable by replacing the piezoelectric transformer  2 . 
     The switch S 1  may be comprised of a power MOSFET, a small floating power supply, an optocoupled driver, and four diodes, as shown in FIG.  5 . Output from the piezoelectric transformer  2  is identified as V 1  and consists of a sine wave. 
     FIG. 6 graphically describes the construction of a desired voltage waveform  53  from a high-frequency AC signal  54  generated by a piezoelectric transformer  2 . The desired voltage waveform  53  is comprised of a rising portion and a falling portion about a crossover point  50 . Rising portions of the desired voltage waveform  53  are produced by selecting the leading edge segment  51  from the high-frequency AC signal  54 . Falling portions of the desired voltage waveform  53  are produced by selecting the trailing edge segment  52  from the high-frequency AC signal  54 . 
     FIG. 7 graphically describes the construction of a desired voltage waveform  67  from a high-frequency DC signal  68  generated by a piezoelectric transformer  2 . Actual voltage  69  typically includes regions of the waveform within tolerance, actual voltage  62  in FIG. 7, and regions of the waveform out of tolerance, actual voltage  63  in FIG. 7, about a crossover point  64 . When the waveform is out of tolerance, trailing edge segments  65  from the high-frequency AC signal  68  are selected to increase the load voltage. 
     FIG. 8 shows an exemplary output signal  8  generated from a high-frequency signal  6 . FIG. 9 provides a detailed view of the output signal  8  highlighting the stepwise feature of the output voltage. Horizontal steps occur when the switch S 1  is OPEN. Vertically increasing and decreasing steps result when switch S 1  is CLOSED. 
     FIG. 10 shows a block diagram comprised of a plurality of paired piezoelectric transformers  2  and circuits  3  forming a power distribution system  12 . A power supply  20  generates, collects, or communicates power from one or more sources, including but not limited to thermal, photovoltaic, AC line and DC line, to a bulk converter  21  where it is converted to a clean DC level power, and thereafter communicated to a power storage element  22 , one example including a battery. Thereafter, power is communicated to two or more dedicated elements  23 . In an alternate embodiment, power is directly communicated from power supply  20  to dedicated elements  23 . 
     Dedicated elements  23  are comprised of a high-frequency AC generator  35  which converts DC power from the storage element  32  or power supply  20  to AC power as shown by supply power waveform  28 , a piezotransformer  26  which transforms the AC power as shown high-frequency signal  29 , and a drive circuit  27  which modifies the signal from the piezotransformer  26  to an output signal  30  compatible with the power requirements of the end device. For example, the drive circuit  27  might modify the signal from the piezotransformer  26  to a sinusoidal, sawtooth, square or other wave required for use by an electrical device. Each dedicated element  23  uniquely provides for the power needs of a load L 1  coupled to the output side connection  24  of the drive circuit  27 . 
     The description above indicates that a great degree of flexibility is offered in terms of the present invention. Although embodiments have been described in considerable detail with reference to certain preferred versions thereof, other versions are possible. Therefore, the spirit and scope of the appended claims should not be limited to the description of the preferred versions contained herein. 
     
       
         
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 Component 
                 Description 
               
               
                   
                   
               
             
             
               
                   
                 Resistor R1 
                 1,000 ohms 
               
               
                   
                 Resistor R2 
                 100,000 ohms 
               
               
                   
                 Resistor R3 
                 1,000 ohms 
               
               
                   
                 Resistor R4 
                 100,000 ohms 
               
               
                   
                 Resistor R5 
                 1,000 ohms 
               
               
                   
                 Resistor R6 
                 1,000 ohms 
               
               
                   
                 Resistor R7 
                 1,000 ohms 
               
               
                   
                 Resistor R8 
                 1,000 ohms 
               
               
                   
                 Resistor R9 
                 1,000 ohms 
               
               
                   
                 Resistor R10 
                 1,000 ohms 
               
               
                   
                 Resistor R11 
                 1,000,000 ohms 
               
               
                   
                 Capacitor C1 
                 1 μF 
               
               
                   
                 Capacitor C2 
                 1 pF 
               
               
                   
                 Comparator X1 
                 NE527, Phillips Semiconductors Co. 
               
               
                   
                 Comparator X2 
                 NE527, Phillips Semiconductors Co. 
               
               
                   
                 Comparator X3 
                 NE527, Phillips Semiconductors Co. 
               
               
                   
                 Comparator X4 
                 NE527, Phillips Semiconductors Co.