WO1999052158A1 - Pulse frequency modulation drive circuit for piezoelectric transformer - Google Patents
Pulse frequency modulation drive circuit for piezoelectric transformer Download PDFInfo
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- WO1999052158A1 WO1999052158A1 PCT/US1999/004870 US9904870W WO9952158A1 WO 1999052158 A1 WO1999052158 A1 WO 1999052158A1 US 9904870 W US9904870 W US 9904870W WO 9952158 A1 WO9952158 A1 WO 9952158A1
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- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N30/00—Piezoelectric or electrostrictive devices
-
- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
- H05B41/00—Circuit arrangements or apparatus for igniting or operating discharge lamps
- H05B41/14—Circuit arrangements
- H05B41/26—Circuit arrangements in which the lamp is fed by power derived from dc by means of a converter, e.g. by high-voltage dc
- H05B41/28—Circuit arrangements in which the lamp is fed by power derived from dc by means of a converter, e.g. by high-voltage dc using static converters
- H05B41/282—Circuit arrangements in which the lamp is fed by power derived from dc by means of a converter, e.g. by high-voltage dc using static converters with semiconductor devices
- H05B41/2821—Circuit arrangements in which the lamp is fed by power derived from dc by means of a converter, e.g. by high-voltage dc using static converters with semiconductor devices by means of a single-switch converter or a parallel push-pull converter in the final stage
- H05B41/2822—Circuit arrangements in which the lamp is fed by power derived from dc by means of a converter, e.g. by high-voltage dc using static converters with semiconductor devices by means of a single-switch converter or a parallel push-pull converter in the final stage using specially adapted components in the load circuit, e.g. feed-back transformers, piezoelectric transformers; using specially adapted load circuit configurations
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
- H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
- H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
- H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
- H02M7/53—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
- H02M7/537—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters
-
- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N30/00—Piezoelectric or electrostrictive devices
- H10N30/40—Piezoelectric or electrostrictive devices with electrical input and electrical output, e.g. functioning as transformers
-
- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N30/00—Piezoelectric or electrostrictive devices
- H10N30/80—Constructional details
- H10N30/802—Drive or control circuitry or methods for piezoelectric or electrostrictive devices not otherwise provided for
- H10N30/804—Drive or control circuitry or methods for piezoelectric or electrostrictive devices not otherwise provided for for piezoelectric transformers
-
- G—PHYSICS
- G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
- G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
- G09G2320/00—Control of display operating conditions
- G09G2320/04—Maintaining the quality of display appearance
- G09G2320/043—Preventing or counteracting the effects of ageing
-
- G—PHYSICS
- G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
- G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
- G09G3/00—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes
- G09G3/20—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters
- G09G3/34—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters by control of light from an independent source
- G09G3/3406—Control of illumination source
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02B—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS
- Y02B70/00—Technologies for an efficient end-user side electric power management and consumption
- Y02B70/10—Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes
Definitions
- This invention relates generally to the field of electrical power circuits for transformers, and in particular, to a pulse frequency modulation drive circuit for a piezoelectric transformer.
- piezoelectric transformers have been proposed for use in power supplies for televisions, photocopiers, LCD backlights, and the like.
- Prior art piezoelectric transformers are based on the well known Rosen design ( see U.S. Patent 2,830,274). These prior art high voltage transformer designs are of a piezoelectric ceramic plate which includes a driving section and a driven section which each have different polarization. The different polarization provide for voltage transformation.
- Piezoelectric transformers are inherently high Q resonators which must be driven at a particular resonant frequency to allow maximum energy transfer to occur for a given output load.
- the resonant frequency point of the piezoelectric transformer is dependent on external variables including time, temperature, output load, and other variables. These variables cause the optimum power output of the transformer to degrade as frequency shifts unless the driving frequency can be continually corrected. If a driving circuit is unable to track the resonant frequency, the piezoelectric transformer will not be operated most effectively.
- the output load voltage or current must be adjustable. Ideally, it is most desirable to operate the piezo-transformer at or near its resonant frequency under all load conditions, while simultaneously providing a means to adjust or regulate the output voltage or current. Of course, high efficiency, simplicity of circuit design, and cost effectiveness are also desired.
- a classic variation of the fixed frequency method involves broadening the inherently narrow bandwidth of a high Q piezoelectric transformer by using an input compensating network consisting of one or more inductors and capacitors.
- One advantage to this method is that a wider operating bandwidth is gained, however, this approach reduces efficiency and adds relatively large and expensive reactive components.
- Another prior art approach controls the drive frequency by using a self-oscillating design in which the piezoelectric transformer becomes part of the feedback loop in a classic oscillator circuit. With appropriate feedback connections, the self-oscillating piezoelectric transformer circuit can track resonant frequency changes automatically. This method does, however, have some practical disadvantages in operation.
- a piezoelectric transformer is a mechanically resonant device.
- the resonant modes of the transformer are determined mainly by the physical dimensions of the transformer device.
- a typical piezoelectric transformer may have multiple resonant modes both above and below the target resonant frequency, including both harmonic and non-harmonic ratios of the target resonant frequency. Several of these modes may have resonant gains which exceed the resonant gain at the target resonant frequency. Oftentimes, it is impractical or impossible to adequately filter or suppress these modes sufficiently to assure that the self-oscillating circuit will always start and maintain its operation at the target resonant frequency.
- VCO voltage controlled oscillator
- this approach does not actually track the high-Q resonant frequency of the piezoelectric transformer, this approach makes use of frequency sweeps to find the initial operating point, to recover from transient conditions, and to respond to changes in the output regulation setpoint.
- the narrowband high-Q characteristics of piezoelectric transformers requires careful initial tuning and accurate operating frequency windows. If the VCO frequency drops below the resonant frequency peak of the piezoelectric transformer, operating instabilities will occur.
- Piezoelectric transformer input sections are characterized by a shunt input capacitance which may exceed tens of nano-farads. It is important to try to minimize harmonic content in the piezoelectric transformer drive waveform. Input drive harmonics may be rejected by the high-Q transformer thereby reducing drive efficiency. Another undesirable scenario would be if the input drive harmonics excited spurious modes in the transformer which would be difficult to suppress.
- Many prior art drive circuit configurations provide direct drive by means of a power amplifier. Power amplifier drivers typically produce a continuous sinewave drive signal which sacrifices efficiency for low harmonic content. Another drawback to power amplifier drivers is that they have difficulty driving large capacitance values.
- Switche Width Modulation Pulse Width Modulation
- the DC voltage supplying the driver circuit is controlled by a either a linear or a switching regulator which in turn is controlled by feedback from a piezoelectric transformer output voltage or current monitor.
- Linear regulators are quite inefficient in this application, so switching regulators are generally preferred.
- switching regulators add their own inefficiency to that of the piezoelectric transformer and the associated drivers.
- Another drawback to switching regulators is that they may also require at least one low-loss power inductor and at least one low ESR output filtering capacitor in addition to the switching regulator controller and the associated power switches.
- resonant drive circuits have been used in the prior art. These resonant drive circuits include those which use an inductor which resonates with the input capacitance of the piezoelectric transformer and those which employ a step-up transformer which resonates with the input capacitance of the piezoelectric transformer.
- a resonant drive circuit which satisfies the accepted criteria for Zero Voltage Switching (ZVS) is a desirable piezoelectric transformer drive configuration. Examples of prior art resonant ZVS drive circuits are shown in Figures 1 through 5.
- FIG. 1 shows a single ended unregulated resonant drive circuit used with both magnetic and piezoelectric transformer power converters in accordance with the prior art.
- a piezoelectric transformer 102 is shown with dashed lines.
- a capacitance C IN is shown across the input of piezoelectric transformer 102 and represents the equivalent input capacitance of piezoelectric transformer 102.
- An input drive frequency 104 is applied to switch S Also included in the circuit is supply voltage V+, reference voltage point V ⁇ and output voltage Vo. Also shown in FIG. 1 is a load resistance R L and an inductance L
- FIG. 2 shows a timing diagram illustrating the circuit waveforms generated by the circuit of FIG. 1 in accordance with the prior art.
- the top waveform shows the S, drive alternatively in the "off and "on” positions at approximately a 50% duty factor.
- N are selected to resonate at the input drive frequency, a pseudo half sinewave drive waveform will be seen at V,. This is also shown in FIG. 2.
- FIG. 3 shows a "push-pull" unregulated resonant drive circuit used with both magnetic and piezoelectric transformer power converters in accordance with the prior art.
- a piezoelectric transformer 302 is provided and shown with dashed lines.
- C, N represents the equivalent input capacitance of piezoelectric transformer 302.
- two switches S, and S 2 are also shown, each connected to a separate inductance L 1 and L 2 , respectively.
- R L is the output load.
- Voltage reference points V, and V 2 are provided on either side of the piezoelectric transformer 402.
- FIG. 4 shows a timing diagram illustrating the circuit waveforms generated by the circuit of FIG. 3 in accordance with the prior art.
- the first two waveforms show switch S ! and switch S 2 , respectively.
- switches S, and S 2 are driven 180° out of phase with each other at approximately a 50% duty factor.
- the third and fourth waveforms show a signal at reference points V, and V 2 , respectively.
- V 1 and V 2 are both alternate periodic positive pseudo half-sinewaves.
- the fifth waveform shows the voltage across (V 2 -V ⁇ ).
- the voltage across (V 2 -V,) produces a full pseudo sinewave across the input of piezoelectric transformer 302.
- Circuits which use the resonant drive approach usually achieve output regulation by employing a switching regulator to control the supply voltage (V+). This has the disadvantages attributed to the use of switching regulators as described above.
- FIG. 5 shows a "push-pull" regulated resonant drive circuit used with a piezoelectric transformer power converter in accordance with the prior art. Most of the elements shown in FIG. 5 have been described in FIGs. 1-4 above and that discussion is incorporated herein by reference.
- FIG. 5 shows a piezoelectric transformer 502 provided in dashed lines.
- FIG. 5 also shows how switch S T and switch S 2 may be connected to a voltage controlled oscillator (VCO) 504 having a VCO-controller 506 connected thereto.
- VCO voltage controlled oscillator
- FIG. 5 also shows an intermittent control 508 having a duty factor control 510 connected to the circuit.
- the prior art circuit of FIG. 5 employs the closed loop "VCO frequency above resonance" approach to regulate the output voltage.
- FIG. 5 also shows a pulse frequency modulation regulation scheme which gates the resonant drive switches with a digital PWM disable signal. By gating the switches "off for variable periods, the average drive power into the piezoelectric transformer can be changed, thus changing the average output voltage or current.
- This approach has several disadvantages in practice, as will be described below.
- This mode of operation can dissipate the resonant energy stored in the piezoelectric transformer and also cause an undesirable shift in the resonant frequency of the transformer. These undesirable effects are repeated each time the resonant drive circuit is cycled by the PWM disable signal.
- a pulse frequency modulation drive circuit for a piezoelectric transformer which controls the piezoelectric output current or voltage by selectively gating integral half cycles of a pseudo-sinewave drive operating at the resonant frequency of the piezoelectric transformer would be a substantial contribution to the art.
- FIG. 1 shows a single ended unregulated resonant drive circuit used with both magnetic and piezoelectric transformer power converters in accordance with the prior art.
- FIG. 2 shows a timing diagram illustrating the circuit waveforms generated by the circuit of FIG. 1 in accordance with the prior art.
- FIG. 3 shows a "push-pull" unregulated resonant drive circuit used with both magnetic and piezoelectric transformer power converters in accordance with the prior art.
- FIG. 4 shows a timing diagram illustrating the circuit waveforms generated by the circuit of FIG. 3 in accordance with the prior art.
- FIG. 5 shows a "push-pull" regulated resonant drive circuit used with both magnetic and piezoelectric transformer power converters in accordance with the prior art.
- FIG. 6 shows a single ended resonant drive circuit for a piezoelectric transformer in accordance with the present invention.
- FIG. 7 shows a timing diagram illustrating the circuit waveforms generated by the circuit of FIG. 6 in accordance with the present invention.
- FIG. 8 shows another embodiment of a single ended resonant drive circuit for a piezoelectric transformer in accordance with the present invention.
- FIG. 9 shows a differential resonant drive circuit in accordance with the present invention.
- FIG. 10 shows a timing diagram illustrating the circuit waveforms generated by the circuit of FIG. 9 in accordance with the present invention.
- FIG. 11 shows a block diagram of a regulated power converter which employs a pulse frequency modulation drive circuit for a piezoelectric transformer in accordance with the present invention.
- FIG. 12 shows a schematic of one embodiment of block 1108 of FIG. 11 in accordance with the present invention.
- FIG. 13 shows a schematic of another embodiment of block 1108 of FIG. 11 in accordance with the present invention.
- FIG. 14 shows a schematic of one embodiment of block 1110 of FIG. 11 in accordance with the present invention.
- FIG. 15 shows a schematic of another embodiment of block 1110 of FIG. 11 in accordance with the present invention.
- FIG. 16 shows a schematic of another embodiment of the pulse frequency modulation drive circuit for a piezoelectric transformer used in a high voltage power converter application in accordance with the present invention.
- FIG. 17 shows a schematic of another embodiment of the pulse frequency modulation drive circuit for a piezoelectric transformer used in a fluorescent lamp power inverter application in accordance with the present invention.
- the present invention is a pulse frequency modulation drive circuit which is well suited for use with a piezoelectric transformer.
- An advantage of this circuit over the prior art is the fact that the piezoelectric transformer may be operated at or near it's resonant frequency under all load conditions, while at the same time providing a simple and efficient mechanism to adjust or regulate the output voltage or current. 10
- the present invention successfully addresses a fundamental problem common in piezoelectric transformer applications, namely that simultaneous resonant frequency control and output level regulation is difficult to achieve with these high-Q narrow bandwidth devices which have an inherently variable resonant frequency.
- the instant invention which provides a circuit which regulates the piezoelectric transformer output current or voltage by selectively gating integral half cycles of a pseudo-sinewave into the piezoelectric transformer at or near the resonant frequency of the piezoelectric transformer.
- the present invention employs a novel switching configuration in the circuit, which will be discussed in greater detail below, which allows the average output of the piezoelectric transformer to be regulated.
- Output regulation is achieved by pulse frequency modulating the input of the piezoelectric transformer with an integral number of half-cycle sinewaves.
- the output of the transformer remains essentially continuous, thereby allowing feedback from the piezoelectric transformer to be used to maintain the drive signal frequency at or near the resonant frequency of the piezoelectric transformer.
- Zero Voltage Switching minimizes switching losses and increases the effective step-up ratio of the piezoelectric transformer.
- FIG. 6 a circuit comprising a first switch S T and a second switch S 2 , as well as an inductor L T and a capacitor C Capacitor C, represents the effective input capacitance of a piezoelectric transformer.
- the value of inductor L T is selected to resonate with capacitor C, at the driven switching frequency of switch S T .
- a supply voltage V+ is shown, as is a voltage reference point V T .
- FIG. 8 An alternative switching configuration which may produce an equivalent gated waveform at voltage reference point V T is shown in FIG. 8.
- FIG. 8 shows another embodiment of a single ended resonant drive circuit for a piezoelectric transformer in accordance with the present invention.
- a circuit having an inductor L, and a capacitor C T along with switches S, and S 2 is provided.
- Input voltage V+ and voltage reference point V T are also provided in this circuit.
- This circuit is similar to the one shown in FIG. 6 (discussed above) with the significant addition of a third switch S 3 .
- switches S 2 and S 3 form a standard totem-pole or half-bridge drive. Switch S 3 is driven approximately 180° out of phase with switch S 2 , and break-before-make switching is assumed.
- the timing diagram waveforms shown in FIG. 7 are also applicable to the circuit of FIG. 8.
- the circuit of FIG. 8 is slightly more complicated with the addition of the third switch S 3 , however, this feature may prove 12
- FIG. 9 shows a differential resonant drive circuit in accordance with the present invention.
- the circuit has four switches, switch S T , switch S 2 , switch S 3 , and switch S 4 , respectively.
- inductors L, and L input voltage V+, as well as voltage reference points V, and V 2 .
- Capacitor C T is also shown in FIG. 9 between V T and V 2 . Capacitor C T represents the effective input capacitance of a piezoelectric transformer.
- inductors L T and L 2 are selected to be resonant with capacitance C, at the driven switching frequency of switches S, and S 2 .
- S 2 and S 4 are closed (in the "on" position"), the circuit in FIG. 9 produces a classic ZVS waveform at V T and V 2 as is shown in the first half of the timing diagram waveform in FIG. 10.
- the differential drive signal across capacitance C T at the input of the piezoelectric transformer will closely approximate a sinewave.
- switches S 2 and S 4 are gated synchronously with the driven frequency of S T , as is shown in the timing diagram of FIG.
- the waveforms at voltage reference points V T and V 2 will consist substantially of an integral number of half-cycle sinewaves as determined by the duty cycle of the S 2 and S 4 control signal. Significantly, there will be substantially no inductive spikes when S 2 or S 4 are placed in the "off position. Furthermore, there will be substantially no capacitive energy dump when S 2 or S 4 are placed in the "on" position and substantially no partial or abbreviated drive cycles are generated.
- FIG. 9 shows, in block diagram form, one embodiment of the pulse frequency modulation drive circuit for a piezoelectric transformer of the present invention.
- the piezoelectric transformer based power converter circuit 1100 is provided in FIG.
- Piezoelectric transformer 1102 couples to a load circuit 1104 which is connected to ground.
- Piezoelectric transformer 1102 also drives a phase triggered oscillator 1108, which is coupled to a synchronous cycle gate control 1110.
- the output level at the load circuit 1104 is monitored by output level sense 1112 which also feeds the synchronous cycle gate control 1110.
- the drive circuit in FIG. 11 is shown as a dashed line area which is numbered 1114.
- Drive circuit 1114 contains a first switch S,, a second switch S 2 , a third switch S 3 , and a fourth switch S 4 .
- Drive circuit 1114 also includes a pair of inductors 1216 and 1216' as well as capacitor 1118 which represents the equivalent input capacitance of the piezoelectric transformer 1202.
- Voltage reference points V T and V 2 are also part of drive circuit 1214 and are used to measure relevant waveforms, and input voltage V+ is provided between switches S 2 and S 4 .
- Synchronous cycle gate control 1110 switches S, and S 3 at approximately a 50% duty cycle, approximately 180° out of phase with each other, at a frequency determined the phase triggered oscillator 1108.
- the values of inductors 1116 and 1116' are selected to resonate with capacitor 1118 at the driven frequency, and satisfy the established criteria for a resonant ZVS drive.
- Resonant frequency control is established by the closed control loop consisting of switches S T and S 3 , piezoelectric transformer 1118, phase triggered oscillator 1108 and synchronous cycle gate control 1110.
- the buffered feedback signal from the piezoelectric transformer 1102 may 14
- the open loop frequency of the oscillator is set near the target operating frequency of the piezoelectric transformer 1102, so that only the target resonant mode of the transformer will be excited at start-up.
- the preferred feedback signal is supplied by an independent tap on the piezoelectric transformer which is specifically designed to monitor the motional current of the piezoelectric transformer.
- a portion of the output voltage waveform of the piezoelectric transformer may be used as a feedback signal.
- the frequency control achieved with this method is monotonic, in other words, stable at only one operating point. This may result in a stable loop phase/frequency control of the operating point of the piezoelectric transformer.
- the oscillator does not function as a VCO which changes frequency to achieve output regulation.
- the only function of the frequency control loop will be to maintain the operating frequency at or just above the target resonant frequency of the piezoelectric transformer.
- the circuit will track changes in the resonant frequency of the piezoelectric transformer due to temperature, mounting stresses, dynamic load changes, and other variables.
- Output regulation is achieved by pulse frequency modulating switches S 2 and S 4 .
- Switches S 2 and S 4 are sequentially switched synchronously with the driven frequency in response to an asynchronous "on/off control signal generated by the output level sense 1112.
- the synchronous cycle gate control 1110 responds to the "on" signal by sequentially enabling switches S 2 and S 4 , and gating an integral number of half sinewave drive waveforms into the input of the piezoelectric transformer 1102.
- the output level sense 1112 will switch to the "off position.
- the piezoelectric transformer 1102 will continue to resonate for a time period determined by both the mechanical Q of the transformer and the input and output loading of the transformer.
- the phase triggered oscillator 1108 will continue to track the resonant frequency of the piezoelectric transformer 1102, and switches S T and S 3 will continue to operate at the driven frequency, thus minimizing energy loss and impedance changes at the transformer input.
- a Rosen-type piezoelectric transformer operating in the length extensional mode, is used in a preferred embodiment of the present invention.
- the circuit of the present invention may be used to drive a multitude of different piezoelectric transformer types which have a variety of different operational modes.
- one of several known output circuits may be used to comprise the load 1104.
- the output of the piezoelectric transformer may be used to drive an AC device directly.
- An impedance matching network may also be placed between the piezoelectric transformer output and the load impedance.
- a rectifier in the form of a diode voltage doubler and a filtering capacitor may be employed.
- the output parameter which is regulated may be either voltage or current.
- Many output circuits are well known in the art and may be easily used in conjunction with the present invention by those skilled in the art.
- FIGs. 12 and 13 may be viewed as alternative embodiments of the phase triggered oscillator.
- FIG. 12 shows a schematic of one embodiment of block 1108 of FIG. 11 , the phase triggered oscillator, in accordance with the present invention.
- a 50% duty cycle squarewave clock is realized with a CMOS 555 timer U1 which is connected in a standard astable configuration.
- Resistor R T and capacitor C T set the nominal frequency of the clock to approximately the target resonant frequency of the piezoelectric transformer.
- An input voltage V+ as well as a feedback signal (FB) are also shown in FIG. 12.
- Appropriate feedback from the piezoelectric transformer is applied to resistor R 3 which serves as a current limiter at 16
- comparator U2 the input to a high input impedance logic gate or comparator U2.
- the output of comparator U2 is applied at the junction of resistor R T and capacitor C T through resistor R 2 .
- FIG. 13 shows a schematic of another embodiment of block 1108 of FIG. 11 , the phase triggered oscillator, in accordance with the present invention. Many of the elements in the circuit of FIG. 13 are similar to those elements described with reference to FIG. 12, discussed above. That discussion is incorporated herein by reference. Referring to FIG. 13, a 50% duty cycle squarewave clock is realized with a CMOS Schmitt trigger inverter U1 which is connected in a standard astable configuration.
- Resistor R T and capacitor C T set the nominal frequency of the clock to approximately the target resonant frequency of the piezoelectric transformer.
- Resistor R 3 which serves as a current limiter at the input to a high input impedance logic gate or comparator U2.
- comparator U2 The output of comparator U2 is applied to the junction of resistor R T and capacitor C, through resistor R 2 .
- the feedback signal from the piezoelectric transformer forces the clock frequency to track the feedback frequency with approximately a 90° phase shift.
- the phase relationship between the feedback signal and the clock can be adjusted over a limited range by adding capacitance to the input of comparator U2.
- FIGs. 14 and 15 are alternate embodiments of the synchronous cycle gate control, described in FIG. 11 as block 1110.
- FIG. 14 is a schematic diagram of one preferred embodiment of the synchronous gate cycle control 1110 of FIG. 11.
- the phase triggered oscillator clock is used as the master timing signal which determines the switching sequence of the four drive switches, S 1t S 2 , S 3 and S 4 respectively.
- Switches S T and S 3 are driven by the clock signal via inverting buffer U3-C and non-inverting buffer U3-D.
- Switches S 2 and S 4 are driven via non- inverting buffers U3-A and U3-B, from the corresponding inverted outputs 17
- U1 is a standard 7474 D-type flip-flop.
- the clock input of U1-A is driven by the clock signal, and the clock input of U1- B is inverted by gate U2.
- the data inputs of U1 are connected to the asynchronous "on/off output of the output level sense circuit (block 1112 in FIG. 11).
- the circuit configuration shown in FIG. 14 realizes the synchronous drive control sequence required to generate the timing diagrams of FIGs. 7 and 10.
- the circuit of FIG. 14 drives switches S T and S 4 such that they synchronously gate integral pseudo half sinewave signals to the input of the piezoelectric transformer. This allows the circuit to achieve closed- loop PFM output level regulation.
- FIG. 15 is a schematic diagram of another preferred embodiment of the synchronous cycle gate control (block 1110 in FIG. 11).
- the circuit of FIG. 15 is similar to that of FIG. 14 and the discussion of FIG. 14 above is incorporated herein.
- One significant difference with FIG. 15 is that the data input of flip-flop U1-A is connected to the non-inverting output of U1- B.
- the circuit configuration shown in FIG. 15 also realizes the synchronous drive control sequence required to generate the timing diagrams of FIGs. 7 and 10.
- the circuit of FIG. 15 drives switches S1 and S4 such that they synchronously gate integral pseudo full sinewave drive signals to the input of the piezoelectric transformer to achieve closed-loop PFM output level regulation.
- a diode voltage doubler may require the first half cycle to charge the series doubler capacitor and the second half cycle to transfer charge to the output capacitor. It will be appreciated by those skilled in the art that other logically equivalent realizations of the circuits of FIGs. 14 and 15 may be constructed. For example, by using a logically equivalent arrangement of NAND gates or NOR gates, a substantially similar result may be achieved.
- FIG. 16 is a schematic diagram of one embodiment of the present invention as applied to a DC high voltage power converter. Many of the elements of this circuit have been discussed previously with reference to FIGs. 6-15 discussed above, and that discussion is incorporated herein. 18
- a piezoelectric transformer 1602 drives a diode voltage doubler consisting of high voltage diodes D, and D 2 and high voltage filter capacitor C,.
- An output load R L is connected across the filter capacitor C T .
- a resistive voltage divider is formed by resistor R T and resistor R 2 and is connected to the inverting input of comparator U1 , which may be an LMC-339 model manufactured by Texas Instruments, for example.
- a voltage reference which sets the regulation level is connected to the non-inverting input of U1.
- the "on/off output signal from U1 is an input to the synchronous cycle gate control circuit 1610.
- the preferred embodiment of the controller circuit for this application is the full sinewave controller shown in FIG. 15.
- a voltage feedback signal from the piezoelectric transformer 1602 is connected to the phase triggered oscillator circuit 1608.
- the preferred embodiment of the oscillator circuit for this application is shown in FIG. 12.
- Switches S T and S 3 are N-Channel Mosfet transistors such as IRF7103 manufactured by International Rectifier.
- Switches S 2 and S 4 are P-Channel Mosfet transistors such as NDS9933 manufactured by Fairchild.
- Power inductors L T and L 2 may be model number DO-5022 manufactured from Coilcraft, for example. Of course, other vendors and manufacturers may also supply such components as are standard in the industry.
- the values of power inductors L T and L 2 are selected so as to resonate with the effective input capacitance of the piezoelectric transformer 1602 at the target resonant frequency of the transformer.
- Piezoelectric transformer 1602 will be operated at or just above it's target resonant frequency under substantially all operating conditions. Moreover, resonant ZVS switching of switches S T and S 3 will be maintained to minimize switch losses.
- the DC high voltage output level will be regulated by closed-loop pulse frequency modulation of the input of the piezoelectric transformer with an integral number of pseudo full cycle sinewave drive waveforms.
- the average power supply current drawn at a constant power supply voltage is approximately proportional to the average DC load current.
- the average DC load current is proportional to the drive duty factor.
- FIG. 17 shows another specific application of the present invention.
- a schematic diagram of an embodiment of a CCFL (fluorescent) inverter in accordance with the present invention is provided.
- a piezoelectric transformer 1702 drives a CCFL lamp.
- the lamp current is rectified in a standard manner by the circuit of diodes D T and D 2 , resistor R réelle and capacitor C
- a voltage proportional to the lamp current is applied to the inverting input of comparator U1.
- a voltage reference which sets the regulation level, is connected to the non-inverting input of comparator U1.
- the "on/off output signal from comparator U1 is an input to the synchronous cycle gate control 1710.
- a preferred embodiment of the synchronous cycle gate control 1710 is the embodiment shown in FIG. 14.
- a voltage feedback signal from the piezoelectric transformer 1702 is connected to a phase triggered oscillator 1708.
- a preferred embodiment of the phase triggered oscillator circuit 1708 for this application is provided as FIG. 12.
- switches S T and S 3 are N-Channel mosfet transistors such as model number IRF-7103 provided by Intemational Rectifier, for example.
- Switches S 2 and S 4 are P-Channel mosfet transistor such as model number NDS-9933 provided by Fairchild.
- Power inductors L T and L 2 may be model number DO-5022 from Coilcraft, for example. The values of inductors L, and L 2 are selected to resonate with the effective input capacitance of the piezoelectric transformer 1702 at the target resonant frequency of the transformer. Piezoelectric transformer 1702 will be operated at or just above it's target resonant frequency under all operating conditions.
- the perceived brightness of the CCFL lamp may be established by regulating the average lamp current by closed loop pulse frequency modulation of the input of the pseudo electric transformer with an integral number of pseudo half sinewave drive waveforms.
- the average power supply current drawn at a constant power supply voltage is approximately proportional to the average lamp current, which in turn is proportional to the drive duty factor.
Abstract
Description
Claims
Priority Applications (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
EP99912289A EP1070356A4 (en) | 1998-04-03 | 1999-03-04 | Pulse frequency modulation drive circuit for piezoelectric transformer |
JP2000542809A JP2002510882A (en) | 1998-04-03 | 1999-03-04 | Pulse frequency modulation drive circuit for piezo electric transformer |
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US09/054,634 | 1998-04-03 | ||
US09/054,634 US6016052A (en) | 1998-04-03 | 1998-04-03 | Pulse frequency modulation drive circuit for piezoelectric transformer |
Publications (1)
Publication Number | Publication Date |
---|---|
WO1999052158A1 true WO1999052158A1 (en) | 1999-10-14 |
Family
ID=21992457
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
PCT/US1999/004870 WO1999052158A1 (en) | 1998-04-03 | 1999-03-04 | Pulse frequency modulation drive circuit for piezoelectric transformer |
Country Status (6)
Country | Link |
---|---|
US (1) | US6016052A (en) |
EP (1) | EP1070356A4 (en) |
JP (1) | JP2002510882A (en) |
KR (1) | KR100629836B1 (en) |
CN (1) | CN1304554A (en) |
WO (1) | WO1999052158A1 (en) |
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EP3447286A1 (en) * | 2017-08-21 | 2019-02-27 | Microjet Technology Co., Ltd | Energy-saving control method of resonant piezoelectric air pump |
Also Published As
Publication number | Publication date |
---|---|
EP1070356A1 (en) | 2001-01-24 |
KR20010042410A (en) | 2001-05-25 |
CN1304554A (en) | 2001-07-18 |
KR100629836B1 (en) | 2006-09-29 |
JP2002510882A (en) | 2002-04-09 |
US6016052A (en) | 2000-01-18 |
EP1070356A4 (en) | 2008-09-03 |
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