A kind of circuit for driving piezoelectric transformer and output voltage control method thereof
Technical field
The present invention relates to transformer interlock circuit field, be specifically related to a kind of circuit for driving piezoelectric transformer and output voltage control method thereof.
Background technology
Piezoelectric transformer is a kind of electronic transformer device, and it utilizes piezoelectric effect, and the second energy transition form by electric energy-mechanical energy-electric energy reaches the transmission of energy.Compare with the traditional electrical magnetic type transformer, piezoelectric transformer has good characteristics such as little, in light weight, the no short circuit puncture of volume, progressively be used widely, as: high voltage source, anion generator, Xerox, alert with middle low power devices such as electric shock device, LCD backlight power supply, low-power laser pipe power supplys.
In the crystal that does not have symmetrical centre, because there is spontaneous polarization in inside, the positive and negative charge center does not overlap and produces dipole moment, and crystals just produces an electric field like this, is the balance internal electric field, plane of crystal just produces space charge, make whole crystal externally show electric neutrality, when external force changed, the dipole moment of crystals changed and makes internal electric field change, the space charge of plane of crystal is also just discharged like this, shows piezoelectricity.Otherwise under certain electric field action, crystal can produce the variation (being inverse piezoelectric effect) of overall dimension.
Piezoelectric transformer has utilized such principle just, as shown in Figure 1, on a piezoelectric transformer (can adopt piezoelectric ceramic piece), input a, b apply an electric field (driving voltage Vin) makes potsherd produce resonance (inverse piezoelectric effect), and change into electric charge output (piezoelectric effect Vout) at the mechanical vibrational energy that output c, d produce high strain, wherein resistance R L is load, for ease of understanding, can be divided into drive part 101 and power generation part 102 with pressing the power transformation depressor to regard as.
Because the driving voltage Vin of piezoelectric transformer is a sinusoidal waveform voltage in the prior art, so the structure of the drive circuit of most of piezoelectric transformer is a half-bridge circuit, as shown in Figure 2, this half-bridge circuit is by metal oxide semiconductor transistor MOS
1And MOS
2Constitute the working bus bar voltage V of the input of half-bridge circuit and direct current shown in Figure 3
1Connect, in this drive circuit, inductance L of series connection before the piezoelectric transformer of being everlasting
1Or LC series resonant circuit.By control MOS
1With input A
1And MOS
2The input terminal voltage A of pipe
2Waveform voltage, drive circuit is with this DC operation busbar voltage V
1Be shaped as sinusoidal voltage V shown in Figure 4
2, and be added to input a, the b of piezoelectric transformer 1.If consider the changing factor of ambient temperature, input voltage, load etc., drive circuit may be complicated a little, but also more practical, as shown in Figure 5, and at the input a of piezoelectric transformer 1 series capacitance C
1, at the input two ends of piezoelectric transformer 1 a, b shunt inductance L
2By inductance L
2And capacitor C
1The LC filter circuit that constitutes is used to remove clutter, and guarantees that piezoelectric transformer still has enough power outputs under the low extraneous input voltage of low temperature.
But no matter the drive circuit of piezoelectric transformer adopts the principle electrical circuit of figure (a), or adopts the practical circuit of figure (b), a common shortcoming is all arranged, i.e. metal oxide semiconductor transistor MOS
1, MOS
2Not the operating state that is in Zero-voltage zero-current, the working bus bar voltage V of its connection
1All the time be in the high direct voltage state, inductance adds that its equivalent Mathematical Modeling of piezoelectric transformer of series connection is generally inductive load, makes electric current with voltage phase difference be arranged again, so metal oxide semiconductor transistor MOS
1, MOS
2Switching loss very big.The drive circuit of above-mentioned piezoelectric transformer has just been applied mechanically the notion of common switching circuit, and practical circuit just adds LC filtering, thereby the shortcoming of switching circuit is eliminated circuit shortage specific aim here.
Piezoelectric transformer has developed into the pure resistance state that itself is equivalent in the prior art, and this piezoelectric transformer presents input voltage and input current same-phase (or differ be π) under a certain operating frequency.Owing to after above-mentioned drive circuit adds the piezoelectric transformer that has equivalent pure resistance state, can't constitute the notion of complex resonance circuit.Therefore must seek a kind of new drive circuit that can adapt to above-mentioned piezoelectric transformer characteristic requirement.
Summary of the invention
The purpose of this invention is to provide a kind of circuit for driving piezoelectric transformer and output voltage control method thereof, this drive circuit is output as the batch (-type) half sine wave voltage, reduced the loss of switching device, can make the entire circuit that comprises drive circuit and piezoelectric transformer be in the complex resonance state, reach and reduce loss greatly, the purpose of raising reliability.
For achieving the above object, the present invention adopts following technical scheme:
A kind of circuit for driving piezoelectric transformer, described drive circuit comprises: the LC series resonant tank, input is connected with direct voltage, and output is connected with piezoelectric transformer; Switch is connected in the two ends of electric capacity in the described LC series resonant tank in parallel; Switch control device is connected with described switch, is used to control the switch motion of described switch, makes the output output batch (-type) semisinusoidal waveform voltage of described LC series resonant tank.
Wherein, described switch is a metal oxide semiconductor transistor, the grid of described metal oxide semiconductor transistor is connected with described switch control device, source electrode is connected with described capacity earth one end, drain electrode is connected with the other end of electric capacity, and described switch control device is controlled the conducting of described metal oxide semiconductor transistor by waveform voltage and ended.
Wherein, the resonance frequency that inductance and electric capacity are determined in the described LC series resonant tank, greater than by the conducting of metal oxide semiconductor transistor with by the operating frequency of determining, the ON time of described metal oxide semiconductor transistor is less than half of the work period of being determined by described operating frequency.
Wherein, described resonance frequency is 1.4~1.6 times of described operating frequency, and described ON time is 0.25~0.4 times of described work period.
Wherein, described resonance frequency is 1.5 times of described operating frequency, and described ON time is 0.4 times of described work period.
Wherein, the capacitance of electric capacity is 32nf in the described LC series resonant tank, and the inductance value of inductance is 84 μ H, and the ON time of metal oxide semiconductor transistor is 6 μ s, and the described work period is 15 μ s.
The present invention also provides a kind of output voltage control method that uses above-mentioned circuit for driving piezoelectric transformer, this method comprises: adjust inductance and capacitance parameter value in the described LC series resonant tank, make the resonance frequency of described LC series resonant tank, greater than the operating frequency of determining by the switch motion of switch, the ON time of described switch, less than half of the work period of determining by described operating frequency, so that the output of described LC series resonant tank is a half sine wave voltage.
Wherein, the pass of described resonance frequency and described operating frequency is: described resonance frequency is 1.4~1.6 times of described operating frequency, and described ON time is 0.25~0.4 times of described work period.
Wherein, this method also comprises step: obtain piezoelectric transformer and be in the required operating frequency of resonance condition; By the relation of described resonance frequency and described operating frequency, the resonance frequency that described LC series resonant tank should reach when determining to reach the complex resonance state; Adjust inductance and capacitance parameter value in the described LC series resonant tank, the resonance frequency of LC series resonant tank is adjusted the described resonance frequency that should reach; According to the equivalent load situation of drive circuit, adjust the ON time of the switch that is connected in parallel on the electric capacity two ends, make output batch (-type) semisinusoidal waveform and reach piezoelectric transformer to be in the required operating frequency of resonance condition.
Use circuit for driving piezoelectric transformer provided by the invention and output voltage control method, have following beneficial effect:
(1) when conducting of metal oxide semiconductor transistor metal-oxide-semiconductor or disconnection, the voltage that links to each other with metal-oxide-semiconductor is zero, so can reduce the switching loss of metal-oxide-semiconductor greatly;
(2) at piezoelectric transformer input voltage u
cNon-vanishing preceding half period, its waveform is half sine wave, is applicable to the demand of piezoelectric transformer offset of sinusoidal driving voltage;
(3) at piezoelectric transformer input voltage u
cBe zero back half period,, can rely on the elastic energy of storage because piezoelectric transformer is an elastomer, the sinusoidal attitude vibration of half period after finishing automatically, so the output of piezoelectric transformer is still a complete sinusoidal waveform;
(4) has equivalent pure resistance characteristic when piezoelectric transformer self, promptly under some operating frequencies, when its input voltage and input current same-phase (or phase difference is π), drive circuit works busbar voltage itself changes in the semisinusoidal mode, adjust its operating frequency like this, just can realize comprising drive circuit and piezoelectric transformer complex resonance characteristic, thereby improve the efficient of entire circuit greatly in interior entire circuit.
Description of drawings
Fig. 1 is the principle schematic of piezoelectric transformer;
Fig. 2 reaches and the piezoelectric transformer connection layout for existing conventional piezoelectric transformer drive circuit structure;
Fig. 3 is the input voltage schematic diagram of circuit for driving piezoelectric transformer;
Fig. 4 is the output voltage schematic diagram of circuit for driving piezoelectric transformer;
Fig. 5 is that practical circuit for driving piezoelectric transformer structure reaches and the piezoelectric transformer connection layout in the prior art;
Fig. 6 is that embodiment of the invention circuit for driving piezoelectric transformer structure reaches and the piezoelectric transformer connection layout;
Fig. 7 is that the preferred circuit for driving piezoelectric transformer structure of the embodiment of the invention reaches and the piezoelectric transformer connection layout;
Fig. 8 is for when the LC series resonance frequency is close with operating frequency or consistent, and the piezoelectric transformer voltage waveform that drive circuit is exported when non-loaded;
Fig. 9 is for when the LC series resonance frequency is close with operating frequency or consistent, and the piezoelectric transformer voltage waveform that drive circuit is exported when load is arranged;
Figure 10 is the output voltage waveforms of drive circuit among the embodiment.
Figure 11 is the output voltage control method flow chart of piezoelectricity transformation drive circuit of the present invention.
Among Fig. 1: 1, piezoelectric transformer; 101, drive part; 102, power generation part;
Embodiment
A kind of pressure power transformation depressor drive circuit that the present invention proposes is described as follows in conjunction with the accompanying drawings and embodiments.
Embodiment
Present embodiment circuit for driving piezoelectric transformer structure reaches and the piezoelectric transformer connection layout as shown in Figure 6, and this circuit comprises: LC series resonant tank, input and direct voltage V
1Connect, output is connected with piezoelectric transformer; Switching device is connected in the two ends of electric capacity in the LC series resonant tank in parallel; Switch control device is connected with switching device, is used for the switch motion of control switch device, makes the output output batch (-type) semisinusoidal waveform voltage of LC series resonant tank.
Be illustrated in figure 7 as preferred circuit for driving piezoelectric transformer structure and reach and the piezoelectric transformer connection layout, the LC series resonant tank is by the inductance L of mutual series connection
3And capacitor C
3Constitute, its switching device is metal oxide semiconductor transistor MOS
3, metal oxide semiconductor transistor MOS
3Grid be connected source electrode and capacitor C with switch control device
3Ground connection one end connects, drain electrode and capacitor C
3The other end connect, switch control device is by waveform voltage control metal oxide semiconductor transistor MOS
3Conducting and end.The input of LC series resonant tank connects DC bus-bar voltage u
i, the input of piezoelectric transformer 1 also is connected in capacitor C in the LC resonant tank
3Two ends a1, b1, so piezoelectric transformer 1 is as the load of LC resonant tank.
By control metal oxide semiconductor transistor MOS
3The voltage of grid input can be realized metal oxide semiconductor transistor MOS
3Conducting with end, this conducting with by having determined MOS
3Operating frequency.Resonance frequency and metal oxide semiconductor transistor MOS when wherein LC series resonant tank
3Operating frequency when consistent, if piezoelectric transformer 1 non-loaded resistance R L (i.e. zero load), when drive circuit and piezoelectric transformer 1 were lossless again, the piezoelectric transformer input was the output (capacitor C of drive circuit
3Two ends) voltage u
cVoltage waveform as shown in Figure 8, be specially a DC component and cosine wave sum.When piezoelectric transformer has load, when circuit is lossy, metal oxide semiconductor transistor MOS
3ON time must be arranged, and the waveform of piezoelectric transformer input as shown in Figure 9.Though because there is certain ON time in the sine voltage of above-mentioned drive circuit output, ON time is too short, and the LC series resonance frequency is close with operating frequency again, not ideal waveform therefore with the above-mentioned drive waveform piezoelectric transformer that has distorted.
In the present embodiment, by to the inductance L in the LC series resonant tank
3Inductance value and capacitor C
3Capacitance make adjustment, make the resonance frequency and the metal oxide semiconductor transistor MOS of LC series resonant tank
3The operating frequency of (being the parallel resonance frequency of transformer) is inconsistent, and the resonance frequency of LC series resonant tank is greater than MOS
3Operating frequency (being the parallel resonance frequency of piezoelectric transformer), MOS
3The ON time of pipe is less than half of the work period of being determined by operating frequency, and preferably the resonance frequency of LC resonant tank is MOS
31.4~1.6 times of operating frequency, MOS
3ON time when being again work period of 0.25~0.4 times, the voltage u at capacitor C two ends
c(being the transformer input terminal voltage) just presents batch (-type) half-sine wave waveform as shown in figure 10, and in the preceding half period in each cycle, output voltage is approximately the half-sine wave shape, in the back half period, then is zero-voltage state.。
Because the resonance frequency f of LC series resonant tank and resonance period T are by the inductance L in the resonant tank
3And capacitor C
3Decision is specially:
(1)
(2)
(3)
Wherein, R
LBe inductance L
3Equivalent internal resistance, L is an inductance L
3Inductance value, C is a capacitor C
3Capacitance, wherein R is the load of drive circuit, is the equivalent load that piezoelectric transformer is seen into from input.
MOS
3Work period T
0For:
T
0=T+τ
2+ε (4)
Wherein, T is the harmonic period of LC series resonant tank, τ
2Be MOS
3ON time, ε is off time, can be for just also can be for negative.
The resonance frequency f of preferred LC resonant tank is set to MOS in the present embodiment
31.5 times of operating frequency, i.e. T
0=1.5T, and τ
2=0.4T
0
During concrete enforcement, τ
2Determine according to the load of the drive circuit piezoelectric transformer of full load (promptly with), by adjusting τ
2Should make drive circuit head half period (or near half period) that comparatively regular semisinusoidal output is arranged, then half period is a straight no-voltage output substantially.Load is heavier, τ
2Bigger, load is lighter, τ
2Fewer, be plus or minus thereby ε may occur.
Drive circuit output voltage u in a half period
cExpression formula as follows:
(8)
Wherein, u
iBe DC input voitage, T
0Be MOS
3The work period of (being the parallel resonance frequency of transformer) (seeing formula (4)), promptly be equivalent to the harmonic period of piezoelectric transformer, τ
2Be MOS
3ON time, T is the harmonic period of LC series resonant tank, ε is off time, R
LBe inductance L
3Equivalent internal resistance, β is tried to achieve by formula (1), ω is tried to achieve by formula (2).
Drive circuit output voltage u in a half period in the following formula (8)
cExpression formula can also adopt following formula to represent:
Wherein, u
iBe DC input voitage, T
0Be MOS
3Work period (seeing formula (4)),, T is the harmonic period of LC series resonant tank, ε is off time, β is tried to achieve by formula (1), ω is tried to achieve by formula (2).
After above parameter by the LC series resonant circuit in the present embodiment is provided with, can make drive circuit output semisinusoidal waveform voltage, the benefit of doing like this is, as metal oxide semiconductor transistor MOS
3When pipe conducting or disconnection, with MOS
3The voltage that pipe links to each other is zero, so can reduce MOS greatly
3The switching loss of pipe; At piezoelectric transformer input voltage u
cNon-vanishing preceding half period, its waveform is half sine wave, is applicable to the demand of piezoelectric transformer offset of sinusoidal driving voltage; At piezoelectric transformer input voltage u
cBe zero back half period,, can rely on the elastic energy of storage because piezoelectric transformer is an elastomer, the sinusoidal attitude vibration of half period after finishing automatically, so the output of piezoelectric transformer is still a complete sinusoidal waveform.
In addition, when piezoelectric transformer self has equivalent pure resistance characteristic, promptly under some operating frequencies, when its input voltage and input current same-phase (or phase difference is π) (reaching resonance condition), drive circuit works busbar voltage itself changes in the semisinusoidal mode, adjust its operating frequency like this, just can realize comprising drive circuit and piezoelectric transformer complex resonance characteristic, thereby improved the efficient of entire circuit greatly in interior entire circuit.
Be as shown in figure 11, the output voltage control method flow chart of circuit for driving piezoelectric transformer, this control method comprises makes drive circuit output batch (-type) semisinusoidal waveform voltage, and further adjust parameter and make its operating state that reaches complex resonance reaching under the semisinusoidal waveform voltage condition, preceding a kind of method is promptly determined parameters relationship earlier: the resonance frequency of LC resonant tank is MOS
31.4~1.6 times of operating frequency, MOS
3ON time when being again work period of 0.25~0.4 times.A kind of method in back comprises step: obtain piezoelectric transformer and be in the required operating frequency of resonance condition on the basis of preceding a kind of method; By the relation of above-mentioned resonance frequency and operating frequency, the resonance frequency that the LC series resonant tank should reach when determining to reach the complex resonance state; Adjust inductance and capacitance parameter value in the LC series resonant tank, the resonance frequency of LC series resonant tank is adjusted the described resonance frequency that should reach, then according to drive circuit equivalent load size, be adjusted to the switching tube ON time, thereby make batch (-type) half sine wave voltage waveform reach comparatively perfectly stage, and reach above-mentioned piezoelectric transformer by the operating frequency that this switching tube ON time is determined and be in the required operating frequency of resonance condition.
In the present embodiment, the voltage of drive circuit input is 42.5V, and when reaching the complex resonance state, inductance and capacitance parameter value in the concrete LC series resonant tank that is provided with are:
L
3=84μH,C
3=32nf,T
0=15μs,τ
2=6μs
By above setting, the maximum of the batch (-type) half-wave sinusoidal voltage of drive circuit output: u
Cmax≈ 126V.
The present invention not only is specially adapted to the drive circuit as piezoelectric transformer, equally also be applicable to as zero voltage switch circuit usefulness, or other needs the circuit of this type of waveform to use.
If the LC series resonance frequency is when being far longer than operating frequency (for example be operating frequency 10-1000 times time), in a work period, half-sine wave just becomes very narrow spike, its peak value can be that tens times of direct-current working volts are to more than the hundred times, form a series of belt lengths high frequency spike string intermittently, this pulse train can be used for the electric light source firing circuit and use.
Above execution mode only is used to illustrate the present invention; and be not limitation of the present invention; the those of ordinary skill in relevant technologies field; under the situation that does not break away from the spirit and scope of the present invention; can also make various variations and modification; therefore all technical schemes that are equal to also belong to category of the present invention, and scope of patent protection of the present invention should be defined by the claims.