DE10259069B4 - Resonant converter and method for driving variable loads - Google Patents

Abstract

Resonant converter for driving variable loads, having the following features:
a piezo transformer (105) having an input port and an output port for providing an output signal for driving the variable load (107);
a switch (103) for providing an input signal from a source (101) to the input port of the transformer (105);
an input inductor (201) connected between the source (101) and the switch (103) arranged in parallel with the input port of the piezo transformer (105);
a controller (109) for controlling a switching frequency of the switch;
wherein the piezotransformer (105) is sized and connected such that when a nominal power is supplied to the variable load (107), a voltage-to-voltage ratio between the input signal and the output signal is from 1.5: 1 to 5: 1; and
wherein the control means (109) is arranged to control the switching frequency of the switch (103) based on a phase shift between a switch current and a load current at variable load and / or varying input voltage.

Description

The The present invention relates to a switching power supply for driving of changeable ohmic-capacitive or ohmic-inductive loads, a resonant circuit, an electromechanical Energy converter having a switch and a control device.

Switching Power Supplies with or without resonant circuit usually do not come without inductive electromagnetic Components out. To achieve a low-loss switching operation can such circuits only up to a certain maximum frequency and only with resonant inductive elements or broadband transformers or inductors operated become. Such components are volume-intensive and cause a significant share of the cost of the entire device.

For example is a self-or externally excited half-bridge circuit to cite the with bipolar transistors, reverse diodes, a series resonant circuit as well as inductive base feedback is working. An exemplary embodiment of such Half-bridge circuit is disclosed in the following specification (1): S. Lowbridge, M. Maytum, K. Rutgers, "Electronic Ballasts for Fluorescent Lamps Using BUL 770/791 Transistors "(Texas Instruments, 1992). The load circuit is predominantly inductive, whereby a low-loss switching in different load cases is possible. This circuit can one also as an amplifier class D class. She had even using minority charge-free MOS transistors (MOS, MOS = Metal Oxide Semiconductor) the disadvantage of capacitive clearances, because the switches must be switched on under voltage, if not an output side resonance choke the voltage at a Turn on about zero above a respective one Switch rises. Consequently will Zero Voltage Switching (ZVS), which is characterized in that when switching a voltage across a Power semiconductors before and during a shift is made to zero, by a sufficient size (Resonance) inductance reached at the load circuit.

Farther There are RF amplifiers (RF, RF = high frequency) Class E with only one switch and a high efficiency. An embodiment of such Circuit is published in the following document (2): N.O. Sokal, A. D. Sokal, "Class E - A New Class of High Efficiency Tuned Single-Ended Switching Power Amplifiers ", (IEEE, Journal of Solid State Circuits, Vol. SC-10, No. 3, June 1975). Such amplifiers become predominantly as transmission amplifiers used and thereby with an externally generated clock at an optimal On-time operated. The switch-on time is usually about half a time Period duration (D = 0.5 corresponds to optimum). D denotes the relative (i.e., on period duration) on-time. These Circuit needed also a resonance inductance in the load circuit, but achieved the zero-voltage behavior (ZVS) parallel to a sufficiently large capacity. While at a half-bridge circuit the parallel capacity as possible to the switch chosen small is to the zero-voltage behavior (ZVS) easily by a resonance to achieve this, the class E is called this parallel capacitance as big as possible made to the maximum voltage across the switch during the Turn off as small as possible to keep. Will the capacity However, too big, so can the voltage will not return to zero and there will be inadmissible turn-on losses on.

at a use of high-frequency piezoelectric transformers (Piezotransformatoren) or other energy converters with an electromechanical Energy transformation can be any transformation ratios Realisie ren, however, these components usually provide no predominantly inductive input behavior. Such electromechanical transducers are usually also very narrow band and can with respect to their frequency behavior only sinusoidal Transmit vibrations. A hard-switching converter topology is therefore for their Operation less suitable. Thus, the resonance mode must, favorably also in a resonance converter topology. Because of a piezoceramic Material essentially a capacitive input and output behavior is given, such a converter, the conventional inductors or Transformers replace only if in the case of a desired inductive Load circuit behavior for additional inductive shaping of the load circuit care is taken. At a Half-bridge circuit Such an inductive load circuit behavior is required to prevent the Keep switching losses small. The simplest measure can be an additional, although small conventional inductance in the load circuit insert. If the Switch-on losses due to correspondingly low input voltage level (eg low voltages up to 24 V) are small enough, can also be a Capacitive behavior of the electromagnetic transducer in the half-bridge acceptable be.

Finally, the switching in a resonance case using a piezoelectric transformer can be designed so that the switching losses are minimized when a Umladezeit the relatively large input capacitances of the piezoelectric transformer by an exact observance of required driving times by a temporary switching off both switches (dead times) is bridged. For this purpose, however, a precisely adjustable high-side and low-side driver circuit is required, which further usually has an integrated circuit. An embodiment of such a circuit is disclosed in the following specification (3): RL Lin, FC Lee, EM Baker, DY Chen, "Inductor-less Piezoelectric Transformer Electronic Ballast for Linear Fluorescent Lamps", APEC2001, Anaheim, CA, Proceedings , Vol. 2, pages 664-669.

In a class E resonant circuit, the predominantly capacitive input behavior of a piezo transformer is beneficial in that the magnitude of the input capacitance can be adjusted to an electrically required value and thus not disturbing, as is the case with a half-bridge or other inductively-acting load circuit. Such class E circuits with a piezoelectric transformer are already known from the following document (4): T.Abe, Sh. Jomura, T. Tamakai, "Discharge tube driving device and piezoelectric transformer," EP 0 665 600 B1 , European Patent of 21.07.1999.

Such Circuits are not in the font (4) for the technically in mains voltage applications given case of a big one Input voltage and a small output voltage used, but to the high transformation of a smaller voltage a larger one used. These restriction to small input voltages was previously mainly due to the lack of Availability dynamically fast, high-blocking circuit breaker, which are now inexpensive can be produced z. B. Fieldstop IGBT (IGBT = Integrated Gate Bipolar Transistor) up to 1700 V or Cool MOS transistors up to 800 V.

at Low voltage applications will use a class E circuit according to script (4) and after writing (2) mostly in optimal operation with the relative On time of D = 0.5 used. Mostly needed one such circuit in the case of the high transformation an additional input parallel capacity, if the input capacity of the piezoelectric transformer is not sufficiently large. This is not given in a Abtransformationsfall, where the input capacitance some embodiments of piezoelectric transformers can be too large.

There are also it Eintransistorschaltungen with a piezotransformer, the one resonance require, which does not, or not exclusively, smoothing and thus for a high Frequency of about 50 to 200 kHz by a suitable choice of one Magnetic material and a stranded wire must be suitable. An embodiment such an arrangement is shown in document (5), US-6,052,300, disclosed. Furthermore prevents an input-side smoothing choke against one input-side smoothing or resonance inductance a direct action of high-frequency current oscillations an input or a smoothing capacitor, so that an input side smoothing choke (hereinafter inductance inductance called) other arrangements of an inductance is preferable.

With regard to the control of circuits with a piezoelectric transducer, phase lock loop (PLL) is a typical way of frequency tuning. In the document (7), US-5,866,968, a way is described, the phase shift between the output voltage and the drive signal of a circuit according to (4) set so that a PLL circuit with a simple oscillator / driver IC can be realized. This class E control circuit is well suited for piezotransformers with high transformation properties, since the maximum voltage at the output of the transformer is a significant point at the same time for the rated power. Because of the low current load in the high transformation, the frequency characteristic of the output voltage will almost correspond to an idle case, so that the transformation ratio between idle and nominal load changes little. In (7) is thus essentially given a phase control on the voltage waveforms between input and output, so that always sets a maximum output voltage when the correct phase position (in this case about 90 ° or slightly less) is set. This also applies to other topologies with strong high transformation of the voltage, for example for the half-bridge circuit. In the case of the transformation, a flattening of the transmission characteristic of the output voltage can be observed, since the secondary-side current load significantly influences the voltage transmission ratio. In this case, with an inaccurate fixation of the nominal point in applications, for example for low-pressure gas discharge lamps or power supplies, very different output powers occur if an adjustment to the phase between the voltages would take place. Gas discharge lamps have a negative differential resistance characteristic, and are sufficiently fixed by the lamp current with respect to their rated power. If one uses the phase shift between the maximum of the output current and an input variable as the basis for a control, so the desired nominal power is hardly adjustable by the Exemplarstreungen of lamp (nominal voltage) and piezotransformer, regardless of the topology. Thus, the control must be made to a certain nominal value of the output current, which is not necessarily the maximum transmittable current is. A fundamental solution for setting a PLL control according to this principle with this same disadvantage has become known from (3). Consequently, for adjusting the lamp current in (3), a very accurate control circuit must be used which either requires a special nominal value adjustment for each device in order to reach the nominal point. Or the value of the output current is sampled with sufficient processing effort. A phase control by sampling the zero crossings of output voltage and output current in a half-bridge circuit is again inaccurate because of the dispersion of Umladezeiten at the input of the piezoelectric transformer, so that there is an evaluation of the amplitude of the output current is required to adjust the rated power.

From "A Very Simple DC / DC Converter Using Piezoelectric Transformers ", M.J. Prieto et al. IEEE, 2001, pages 1755 to 1760 are power supplies with piezo transformer in a half-bridge topology known.

From the EP 0782374 A1 and the US 6144139 Converters with piezoelectric transformers are known, which are switched on the primary side via a switch, wherein the control of the switch is effected by a phase comparison between input voltage and output voltage. From the US 6348755 B1 a converter with a piezoelectric transformer is known, which is switched on the primary side via a switch, wherein the control of the switch is effected by a phase comparison between input voltage and input current. From the US 6013969 a converter with a piezoelectric transformer is known, which is switched on the primary side via a switch, wherein the control of the switch is effected by a phase comparison between input voltage and output current.

The The object of the present invention is a resonance converter and a method for efficiently driving variable loads to accomplish.

These Task is by a resonant converter to drive variable Loads according to claim 1 and a method for driving variable loads according to claim 14 solved.

Of the The present invention is based on the finding that a piezotransformer to drift changeable loads in a nominal load operation for the transformation case can be used by a switch for switching an on the piezotransformer applicable voltage signal is used, its switching frequency based on a phase shift between a switch current and a load current is controlled.

By the presented invention will be a switching power supply or oscillator defined, which in principle like an amplifier Class E with a piezoelectric transformer is, however, in its mode of operation of an optimum, by D = 0.5 is given, deviates downwards, so that the switch current while the ON time is only increasing, where D typically in an interval of 0.25 to 0.45, and a maximum of one Switch voltage to about three times the value of the input voltage becomes limited. D is here as the relative switch-on time only the positive History of the switch current considered. Additionally one can and should negative switch current waveform by e.g. an antiparallel diode to the switch in all operating cases occur, whereby the zero voltage switching (ZVS) always guaranteed can be.

This measure for sensibly limiting the switch voltage in mains voltage applications is from document (6), EP 0 681 759 B1 and also known in the following specification (8): LR Nerone, "Novel Self-Oscillating Class E Ballast for Compact Fluorescent Lamps", IEEE Trans. on Power Electronics, Vol. 16, No. 2, March 2001, pages 175- Thus, a rectified mains voltage of about 80 to 150 volts or 170 to 260 volts can be applied to an input of a class E amplifier without exceeding a respective maximum voltage limit of the switch (eg 600 V for 120 V AC and 1200 V for 240 V AC.) In addition, a piezoelectric transformer can be connected directly in parallel to a switch, which takes the Abtransformation to the load and by its capacitive input behavior a desired return of the switch voltage to zero over a defined load or Input voltage range guaranteed.

In order to avoid the need for additional reactive load circuit components in this circuit, a voltage transformation ratio of the piezoelectric transformer is just chosen to match the load impedance, and an input capacitance of the piezotransformer is chosen so that it can resonantly store the required reactive power contribution, so that neither the Switch voltage is exceeded, nor does the voltage return to zero. Compared with the circuit according to document (4), the external capacitance shown there in parallel with the switch is superfluous because the input capacitance of the piezoelectric transformer is sufficient for a mains voltage application can be chosen large, while their value in low voltage applications of a piezoelectric transformer is less well achieved and may be too small.

In addition, the required inventive circuit comparatively to half-bridge circuits for mains voltage applications only a low-side driver and thus has a reasonable tax expense on. This simplifies the control effort for the entire Circuit and with a driving effort of a hard-switching DC-DC converter (flyback or Boost arrangement) comparable.

Besides that comes the switch only for a short time, and comparable to the effect a power source, in a reverse mode and therefore operates in particular when using MOS transistors, but also when using IGBT with reverse diode even at high frequencies up to over 100 kHz very low loss.

The present invention enables it, within certain limits changeable Loads with low loss and with a simple driving effort at high frequencies to drive, with only a minimal amount of circuitry, including, for example a switch (MOSFET or IGBT with a reverse diode), a Input DC reactor (reactor inductance) and an electromechanical Energy converter (piezoelectric transformer) is obtained. there is a rectified mains voltage with certain fluctuations the input voltage as well as a constant input DC voltage. The converter (resonant converter) generates because of a high quality of the electromechanical Transformers a nearly sinusoidal output voltage, thereby the crest factor at downstream ohmic loads, such as Gas discharge lamps, can be kept sufficiently small. This is in a conventional circuit, such as for example is disclosed in the document (2), only possible with a large load circuit quality, which again an increased Current density loading of a decoupling capacity, as well as a switch-parallel capacity result would have. The so used circuit works low loss and the maximum Usable frequency is essentially only through the dynamic Losses of the switch limited. A fieldstop IGBT is through his short tail time and a relieved switch off for this application very well suitable.

Consequently In the invention, few inexpensive components are combined in such a way that that the technical Requirements for the derivation from rectified mains voltage for typical Burning voltages for Low-pressure gas discharge lamps are met. At the same time the electromechanical transducer (piezoelectric transformer) the demand the Auftransformation in an unloaded state, so that a low pressure gas discharge lamp easily ignited can be. Before the ignition represents such a lamp is a very large resistance, which in an ignited Condition (combustion mode) in a defined load with a negative passes differential resistance, and approximately be approximated with an ohmic resistance at an operating point can. The realized by other components in a conventional ballast ignition circuit can in a ballast with a piezoelectric transformer exclusively through This transformer can be realized, resulting in a further cost reduction brought becomes.

Farther is due to an utilization of a load-dependent phase shift between a load current and a switch current such a rated load point set this via a phase locked loop (PLL = Phase Lock Loop) can be controlled. It can at a sufficient bandwidth of a piezoelectric transformer a simple integrated drive circuit can be used. A Detecting an input or a lamp voltage is to a setting of an operating point not required, as a parameter dependence a phase shift is small enough to be alone over one Setpoint adjustment of the phase shift to adjust the lamp power. Also has the Amplitude of output current for approximate power adjustment not be sampled because of the change in the transformation ratio at load change the rated power is accurate enough to the phase shift of the current zero crossings of Can map switch and load current.

preferred embodiments The present invention will be described below with reference to FIGS enclosed drawings closer explained. Show it:

1 a rough block diagram showing a basic structure of a resonance converter according to the invention;

2 a circuit diagram of a resonant converter, wherein a control device for controlling the switching frequency of the switch is not shown;

3 a detailed circuit diagram of the resonance converter 2 ;

3a a frequency-dependent voltage Transfer function of a piezoelectric transformer in no-load ignition and in load operation.

4 qualitative curves of a switch current I _S and a load current I _L ;

5 and 5a Curves of a phase angle Φ _LT as a function of the frequency, as well as frequency-dependent voltage transfer functions as a function of the output load and the input voltage;

6 the phase angle Φ _LT at a constant frequency as a function of an input voltage U _in ;

7 a variable load driving circuit according to another embodiment of the present invention; and

8th a drive circuit according to another embodiment of the present invention;

In 1 is shown a rough representation of a resonant converter according to the invention, which is a source 101 , a switch 103 , a piezotransformer 105 , a variable load 107 and a control device 109 includes. One from the source 101 supplied voltage or a current supplied by this is by means of the switch 103 connected at a switching frequency, whereby the piezoelectric transformer 105 an input signal is applied, which is converted into an output signal having a frequency that depends on the switching frequency of the switch 103 depends. This output signal is used to drive a load 107 , For example, a low-pressure gas discharge lamp, the load characteristic is variable. The switching frequency with which the switch 103 is switched by the controller 109 based on a phase shift between the current through the switch 103 and the load current through the load 107 controlled. This phase shift can consist of several signals, for example, before and after the piezoelectric transformer 105 as well as before or after the switch 103 can be determined.

2 shows an embodiment of a resonant converter, wherein a control device for controlling the switching frequency is not shown. This is the source 101 with a first connection 2011 an input choke 201 coupled. A second connection 2013 the input choke 201 is with a first entrance 1031 of the switch 103 coupled. The first entrance 1031 of the switch 103 is with a first connection 1051 an entrance gate 1052 coupled to the piezoelectric transformer. The source 101 is also with a second input 1033 of the switch 103 coupled further to a second terminal 1053 of the entrance gate 1052 of the piezotransformer 105 is coupled. The variable load 107 is between a first connection 1055 an exit gate 1056 of the piezotransformer and a second terminal 1057 the output gate 1056 connected. The desk 103 also has a control input 1035 on, to which a control signal can be applied, the switching frequency of the switch 103 controls. The following is the operation of the in 2 described resonant converter described in more detail.

From the source 101 , which may be a DC voltage source, becomes an approximately constant or sawtooth DC current across the input choke 201 fed. The desk 103 is operated with a relative switch-D and an operating frequency f, so that a resonance of the transducer 105 is reached, and an output signal, such as a voltage, the variable load 107 , For example, a gas discharge lamp or other ohmic-capacitive load drives.

3 FIG. 12 is a detailed circuit diagram of a resonant converter including a class E amplifier. FIG. The source 101 is first with the first connection 2011 the input choke 201 coupled. The second terminal of the inductor inductor is connected to the first input 1031 of the switch 103 coupled, the first input 1031 further to the first port 1051 of the converter 105 is coupled. The source 101 is beyond that with the second entrance 1033 of the switch 103 coupled, the second input 1033 further to the second terminal 1053 of the converter 105 is coupled. Between the first connection 1055 and the second port 1057 the output gate of the converter 105 is the burden 107 arranged. The desk 103 In this embodiment, a voltage controlled power switch is included 1037 , its source or emitter with the first input 1031 of the switch and its drain or collector to the second input 1033 of the switch 103 ge are coupled. The control input 1035 of the switch 103 is in this embodiment simultaneously as a gate of the voltage-controlled circuit breaker 1037 executed. Between the second entrance 1033 and the first entrance 1031 is a diode in the flux direction 1039 connected.

Furthermore, in 3 a simplified equivalent circuit diagram of a piezotransformer 105 shown. The equivalent circuit includes an input capacitance 10501 that between the first connection 1051 and the second port 1053 the input gate of the piezotransformer 105 is switched and thus parallel to the switch 103 is arranged. Fer ner includes the equivalent circuit of the converter 105 a resonant circuit consisting of a series circuit of a capacity 10502 , an inductance 10503 as well as a resistor 10504 consists. In addition, the equivalent circuit of the converter includes 105 a transformer arrangement 10505 , whose inverse transfer ratio 1 / ü (1 / ü = effective input voltage to effective output voltage) is frequency-dependent and according to the invention in a nominal load operation in which the reactive power component is smaller than the active power component, between 1.5: 1 and 5: 1. The resonant circuit, which is further characterized by a high quality, consists of the capacity 10502 , the inductance 10503 as well as the resistance 10504 , is between the first connection 1051 of the converter 105 and another connection 10506 a primary side of the transformer arrangement 10505 connected. Parallel to a secondary side of the transmission arrangement 10505 is an output capacity 10508 arranged.

The piezotransformer 105 is characterized in that the transmission ratio ü as a function of the load 107 is subject to change. The between the connections 1055 and 1057 switched gas discharge lamp 301 that caused by the load resistance 107 is embodied as a load connected to the converter. The voltage controlled circuit breaker 1037 For example, a fast IGBT (eg, a fieldstop IGBT) or a MOS transistor (eg, a cool MOS transistor) may be used with an antiparallel reverse diode. The following is the operation of the in 3 illustrated circuit explained.

Will the voltage controlled circuit breaker 1037 by applying a control signal to the control input 1035 made conductive, so a current flowing through the voltage controlled circuit breaker, due to the input choke 201 do not rise suddenly. In addition, the input capacity 10501 of the converter 105 discharged. Will the voltage controlled circuit breaker 1035 switched off by applying a corresponding control signal again, ie transferred to a blocking state, so a voltage across the voltage-controlled circuit breaker grows slowly, since the input capacitance 10501 charging. Due to the effect of the resonant circuit of the converter 105 in the steady state is despite positively flowing further input current through the throttle 201 achieved a current reversal in the switch, which also reduces the capacity 10501 is unloaded again. The voltage across the switch 103 Thus, it returns to zero, and a negative current begins to flow through the switch. The freewheeling diode 1039 has the task, even before switching on the voltage-controlled circuit breaker 1037 to conduct a reverse current. In this case, a relative or an absolute switch-on time of the switch remain close to constant, since the diode does not have to be switched, but is subject to a current-controlled mode of operation. As long as the diode carries the reverse current, the voltage-controlled circuit breaker at the gate 1035 Therefore, with respect to collector / emitter or drain / source are de-energized, so that no turn-on incurred. Such a current-controlled antiparallel diode is not necessarily designed as a fast diode, so that in this case also a low-cost slow diode can be used.

Will now the switch 103 operated at a predetermined frequency, so is the resonant circuit, consisting of the capacity 10502 , the inductance 10503 and the resistance 10504 , excited. If a resonant frequency of the resonant circuit is reached, the converter reaches 105 a maximum voltage transfer ratio ü. When using a piezoelectric transformer, for example, a voltage transfer function (at a defined input voltage 101 and a defined load 107 ) in terms of frequency as described by a Gaussian function (bell curve), as for example in 3a is illustrated. At a resonant frequency f _R , the voltage transfer function reaches a maximum value in the load state. If the resonance frequency f _{R is} exceeded, which corresponds to an over-resonant case, then the voltage transfer function decreases such that it follows a course of the Gaussian curve. For example, at a frequency f ₁ above the resonant frequency, the voltage transfer function has assumed a value that is significantly less than the value of the voltage transfer function in the resonant case. If the frequency decreases again in the over-resonant mode, the voltage transfer ratio ü increases again.

This frequency-dependent voltage transfer ratio of a piezoelectric transformer, which in 3a is now exploited in accordance with the present invention to drive variable loads. The on the secondary side of the transformation arrangement 10505 exemplary connected gas discharge lamp is characterized by a variable load characteristic. In order to ignite a gas discharge lamp, it is necessary that at the output port of the converter 105 a high voltage is applied, which is the ignition of the gas discharge lamp 301 allows. Will the gas discharge lamp 301 ignited in the no-load condition, so decreases the at the gas discharge lamp 301 voltage applied while the load current flowing through the gas discharge lamp grows. If a rated load operation (load condition) is reached, ie the gas discharge lamp is switched to a combustion mode, then can its load behavior, as already stated, be approximated by a variable resistance at each operating point, wherein a negative differential characteristic of the ohmic resistance occurs.

Now, the voltage transfer function by a suitable design of the electromechanical transducer 105 chosen so wide that at a deviation from the resonant frequency, a suitable reduction of the voltage transfer ratio occurs, it can be counteracted an increase in a voltage at the gas discharge lamp during load operation. If the output voltage rises between the first terminal 1055 and the second port 1057 of the converter 105 On, so does the piezoelectric transformer because of its capacitive output due to the capacity 10508 like a class E converter with a predominantly capacitive output load. As a result, the transmitted total power does not decrease to such a degree as if a constant ohmic resistance were operated as a load with the same frequency change. The transmitted total power is divided into over capacity 10508 guided reactive power and the over the load 107 guided active power. By a decrease in the load current, but a simultaneous increase in the load voltage (burning voltage), the transmitted total power can drop less with a deviation from the resonant frequency less than a constant ohmic load with the same converter, as a larger capacitive reactive power due to larger output voltage on the capacity 10508 to be led.

Furthermore, the piezotransformer 105 designed so that it at about a same or only a slightly different resonant frequency with respect to the load case (ie, burning operation of the gas discharge lamp) generates a loadless up transformation of the output voltage, so that an ignition of the gas discharge lamp is made possible. This property is achievable in piezoelectric transformers due to an undamped mechanical vibration in a no load condition in a simple and cost effective manner by the in 3a shown resonance curve in the loadless state is narrowband, and the broadband resonance curve in the load state, the narrowband load-free curve encloses.

4 shows a diagram of the qualitative curves of the switch current I _S , load current I _L and to be detected phase angle Φ _LT . In addition, a period T, a switch-off time t _off , a reverse time t _rev and the turn-on time t _on are shown. The phase angle Φ _LT , which is determined by the zero crossings of the switch current I _S and the load current I _L is not zero and relatively large in this exemplary diagram, since the load current I _{L has} a larger capacitive component, which is equivalent to the fact that Gas discharge lamp has not yet been converted to its nominal operation (approximately ohmic resistance), where the phase angle Φ _{LT is} smaller and may even become almost zero. At the same time, the reverse time t _rev becomes ever smaller and can become almost zero, so that the negatively flowing reverse current through the diode 1039 disappears.

The frequency-dependent voltage transfer ratio of a piezoelectric transformer is described in the 3 embodiment exploited according to the invention exploited to realize a frequency-dependent power transmission in response to a variable load, as already based on 3a has been explained. This will be explained below with reference to 5 represented voltage transmission ratio of a piezoelectric transformer 105 as a function of a load characteristic of a gas discharge lamp 301 explained in detail.

In most piezotransformers, the resonant frequency in unloaded operation is higher than the optimum frequency under load (for example, for maximum power or for maximum efficiency). To use this property for a control on a gas discharge lamp, the resonant frequency of the electromechanical transducer is realized without load only slightly above the resonant frequency under load, which is technically easily possible by a suitable design of a piezoelectric transformer. The rated frequency for the nominal load combustion mode is intended to coincide approximately with the resonant frequency in a no-load condition. For switching on the gas discharge lamp, the converter is first of all driven, starting from the resonant frequency, with a frequency which is preferably variable around the no-load resonance point, which increases slowly and / or is slowly lowered again, and has a course in FIG 5 illustrated curve 501 the voltage transfer ratio follows.

After detection of a decreasing reverse current passing through the switch 103 flows, and a sufficiently large gas discharge lamp current, ignition of the gas discharge lamp can be determined, as in 5 is shown for the überresonanten case. Immediately after the ignition of the gas discharge lamp, the voltage applied to it decreases, the load current increases, with the result that the voltage transmission ratio is lower, as shown by the curve 503 is shown (capacitive load). The course of the voltage transfer ratio in a burning operation of the gas discharge lamp is through the bend 505 described. Starting from the in 5 shown courses of the various voltage transfer ratios as a function of the load behavior of the gas discharge lamp and the frequency is now clear that the frequency-dependent voltage transfer ratio can be used to efficiently control a given output to the gas discharge lamp by the piezotransformer 105 is excited at different frequencies lying close to each other, which, for example, by a suitable switching frequency of the switch 103 can be realized.

According to the invention, a phase angle φ _LT between the load current and the switch current is evaluated for controlling and regulating the converter constructed in this way in order, for example, to realize a superresonant control.

In 5 Furthermore, an exemplary profile of the phase angle Φ _LT, for example, at rated load as a function of the frequency (curve 507 ) together with the voltage transfer functions in a no-load state (ignition) and in a load state (rated load). It can be seen that the phase angle Φ _LT steadily decreases until a maximum power transmission is reached, while it increases in the direction of load-free operation. In this case, the load changes so that below f _OPT the rated load or an even larger load (small voltage transfer ratio ü) occurs, and above f _OPT a smaller load (greater voltage transfer ratio ü) up to the no-load ignition characteristic in association with the function of the phase angle Φ _LT 507 occurs.

For example, the supersorant range above a frequency f _opt can be used for controlling or regulating the gas discharge lamp power. Accordingly, it is therefore not necessary to detect a maximum value of the gas discharge lamp current to perform the control or the regulation of the converter. It is sufficient to sample the phase angle Φ _LT between the switch and the load current and set it to a nominal value. If the frequency becomes smaller, the active power transfer increases in an over-resonant operation up to its maximum at the resonance frequency.

This has the consequence that a capacitive portion of the load current decreases and the gas discharge lamp current, which approximately in the ignited gas discharge lamp (combustion) approximately in phase with the lamp voltage, comes closer to the phase of the switch current. The switch current embodies about the input current of the piezotransformer during switching on 105 , which is about the transformation ratio on the load (gas discharge lamp) and on the output capacity 10508 of the converter 105 distributed.

Furthermore, in 5a a dependence of the output power transfer from the input voltage at a constant output impedance is shown. Power may be below rated load by increasing the input voltage from a minimum rated input voltage 505 ' over a higher input voltage 503 ' up to a maximum load characteristic 501 ' be increased. In addition, the output power can not be increased significantly, this being dependent on the volume of the piezoelectric transformer used. A smaller volume allows only a smaller maximum load. It is therefore important to ensure that the piezotransformer is designed at least for a load slightly greater than the rated load, so that the control circuit after 8th remains functional beyond the nominal load.

The course of the phase angle Φ _LT at a constant frequency is again in 6 as a function of an input voltage U _in applied to the gas discharge lamp. At a rising voltage U _in the phase angle Φ _LT decreases, since in this case more active power is transmitted to the gas discharge lamp, see eg 5a , over-resonant operation. This has the consequence that the active component of the lamp current increases. From this example it is clear that variations in the input voltage U _in reflected also in the size of the phase angle Φ _LT. In addition, such fluctuations of the voltage U _{in can be} compensated by more power is passed to the gas discharge lamp by lowering the frequency at a falling input voltage U _in in the over-resonant mode of operation. With increasing input voltage, less power can be transmitted to the gas discharge lamp by increasing the frequency. If the phase angle is kept approximately constant, the transmitted active power at the load also remains approximately constant. Since the gas discharge lamp keeps the output voltage almost constant due to its weakly negative differential ohmic resistance, an approximately constant phase angle φ _{LT can be} set by setting a different transmission ratio u as a function of the input voltage. This phase angle is at a constant output voltage due to the parallel connection of the approximately constant capacitance 10508 and the load 107 In load operation, a measure of the size of the load current, and thus the output power.

In 7 an embodiment of a resonance converter according to the invention for low-pressure gas discharge lamps including switching frequency control is shown. Since this Ausführungsbei play on the in 3 In the following, the functionalities are not described again with the same reference numerals.

In addition to the in 3 illustrated embodiment includes in 7 illustrated embodiment, first an input rectifier 701 with a first network connection 70101 and a second network connection 70103 , Between an exit 7015 and an entrance 7017 of the input rectifier 701 is a capacity 703 , which may be, for example, a charging capacitor coupled. Parallel to the capacity 703 is also a driving part 705 together with a resistance 70501 coupled. The exit 7015 of the input rectifier 701 is also connected to the first port 2011 the input choke 201 coupled. The driving part 705 also has a control output 7051 on, according to the present invention with the control input 1035 of the switch 103 in this embodiment, the current-controlled circuit breaker 1037 comprises, is coupled. The driving part 705 also has a first input 7053 as well as a second entrance 7055 on. The first entrance 7053 is with the second entrance 1033 coupled to the switch. Between the first entrance 7053 of the control part 705 and the entrance 7017 of the input rectifier 701 is also a sense resistor 707 arranged. Between the load 107 and the second port 1057 of the converter 105 is a second sense resistance 709 arranged. The second entrance 7055 of the control part 705 is between the load 107 and the second sense resistor 709 coupled.

The driving part 705 also has a power supply input 70157 on that with the entrance 7017 of the input rectifier 701 about a capacity 70111 , which may be implemented as a blocking capacitor, for example. Between the second connection 1053 of the converter 105 and the power supply input 1057 of the control part 705 is a first diode 70131 coupled in the direction of flow. Between the entrance 7017 of the input rectifier 701 and the first connection 1051 the input gate of the converter 105 is also a parallel circuit consisting of an external capacitance 70151 as well as a diode 70171 , which is operated in the flow direction coupled. The following is the operation of the in 7 explained resonant converter explained. However, it does not deal with the functionalities again, which are based on the in 3 have already been discussed embodiment.

The task of the control part 705 is the in 7 detected with an arrow switch current I _S and the load current I _L suitable to determine a phase difference between the two currents, and so at the control output 7051 a control signal for controlling the switching frequency of the switch 103 issue. For this purpose, first of all a variable dependent on the switch current I _S is generated, which at the first input 7053 of the control part 705 can be applied. In this embodiment, the scarf terstrom I _S at the first sense resistor 707 converted into a voltage at the first input 7053 is applied. It should be noted, however, that the size dependent on the switch current can be generated by any functionality, such as a current mirror or a current-controlled voltage source.

On the output side, the piezotransformer drives 105 with a voltage transfer ratio ü a gas discharge lamp with the load resistance 107 through which the load current I _L flows. For detecting a dependent of the load current I _L size is in the in 7 shown embodiment, a second sense resistor 709 used so that the load current I _L across the resistor 709 generates a voltage at the second input 7055 of the control part 705 is applied. On the basis of these two voltages is in the Ansteuerteil 705 First, the phase difference between the switch current I _S and the load current I _{L is} determined, and it is, as has already been described above, a control signal is output, which is the switching frequency of the switch 103 controls.

The resistance 70501 supplies a start supply of the control part 705 , The power supply of the control part 705 is via a primary-side terminal of the piezoelectric transformer 105 via a pump circuit with the diodes 70131 and 70171 , as well as about the external capacity 70151 realized while the capacity 70111 (Block capacitor) the supply voltage of the control part 701 smoothes. Thus, a simple power supply device according to the present invention contains only three capacities without any special requirements for electromagnetic compatibility and without further options for dimming or power factor correction 703 . 70111 and 70151 , which are for example designed as capacitors, an input rectifier 701 (Mains rectifier), an input choke 201 , a piezotransformer 105 for example a fast IGBT 1037 with a reverse diode 1039 , a possibly integrated control unit 705 , two diodes 70131 and 70171 as well as some tiny resistors.

The ballast thus obtained can thus be accommodated in a compact design in the smallest space, for example, a height of 10 mm is easily accessible. For the input choke 201 (Inductance inductance) is, for example, a size EF 13 up to a power of 18 Watts enough. For the piezoelectric transformer 105 For example, a cylindrical design with a height of 9 mm and a diameter of 20 mm can also be considered sufficient for 18 watts. The transistor 1037 , for example, implemented as field stop IGBT, can be accommodated in a small SOT package and the drive circuit (IC) for the driver circuit 705 can be packed in an 8-pin standard housing. A complete integration of the reverse diode 1039 for example a field stop IGBT 1037 As well as a drive IC, in an 8-pin package as a multi-chip solution also cost feasible.

In 8th is an embodiment of the control device according to the invention 109 together with the switch 103 as well as the load resistance 107 shown.

The control device 109 initially includes a device 801 for detecting a size dependent on the switch current I _S , means 803 for detecting a dependent of the load current I _L size and a phase locked loop 805 , The phase locked loop 805 includes in this embodiment a device 807 for determining the phase shift between the switch current and load current from that of the device 801 and from the institution 803 recorded sizes. The device 807 has a first entrance 8071 , a second entrance 8073 as well as an exit 8075 on. The exit 8075 the device 807 is about a resistance 8091 and a capacity 8093 coupled to a reference potential, such as ground.

The device 805 also has a voltage controlled oscillator 811 (VCO, VCO = Voltage Controlled Oscillator) and a gate driver 813 on. An entrance 81101 of the VCO 811 is between the resistance 8091 and the capacity 8093 coupled. An exit 81103 the VCO is connected to an input of the gate driver 813 coupled, whose output to the control input 1035 of the switch 103 is coupled. The device 801 has a comparator in this embodiment 8011 on with a first input 80111, a second input 80112 as well as an exit 80113 on. The first entrance 80111 of the comparator 8011 is with the second entrance 1033 of the switch 103 coupled. The second entrance 80112 is with the exit 80131 a reference source 8013 coupled. The exit 80113 of the comparator 8011 is with the first entrance 8071 the device 107 coupled. The device 803 includes a comparator 8031 with a first entrance 80311 and a second entrance 80312 as well as an exit 80313 , The first entrance 80311 of the comparator 80131 is between the resistances 107 and 709 coupled. The second entrance 80312 of the comparator 8031 is with the exit 8031 the reference source 8013 coupled. The exit 80313 of the comparator 8031 is further to the second input 8073 the device 807 coupled.

The following is the operation of the in the in 8th illustrated embodiment explained.

In the in 8th illustrated embodiment, the switch current to the sense resistor 707 converted into a voltage at the first input 80111 of the comparator 8011 is applied. At the second entrance 80112 of the comparator 8011 is a reference signal from the reference source 8013 is delivered. The comparator 8011 thus samples the zero crossings of the switch current I _S by a comparison between that on the sense resistor 707 abfal loin voltage and the reference signal near zero. At the exit 80113 of the comparator 8011 Thus, an output signal is output, the current phase of the comparison between the at the inputs 80111 and 80112 applied signals and in this embodiment represents a dependent of the switch current I _S size. A symmetrical arrangement is located on the load side. At the scythe resistance 709 the load current I _{L is converted} into a voltage which is at the first input 80311 is applied. At the second entrance 80312 is also the reference signal 80131 to that from the reference source 8013 is delivered. By comparison with the reference signal near zero, the load current through the sense resistor 709 sampled and the comparator 8031 gives at his exit 80313 an output representing a magnitude dependent on the switch current I _L. In this embodiment, the two second inputs 80112 and 80312 with the same exit 80131 the reference source 8013 coupled. This reference source is designed in this embodiment as a DC voltage source. It should be noted that the reference source 8013 may be any source, such as an AC voltage source, or other arrangement such as a current or voltage controlled voltage source that provides a predetermined, eg, time-dependent reference signal.

In the in 8th illustrated embodiment, the switch current and the load current to the two sense resistors 707 and 709 sampled. At this point it should be noted that as the switch current and the load current can be sampled using any functionality, such. As a current mirror with a resistor as a load or a current-controlled th voltage source, or by a separate load or switch current proportional signal source, eg as a tap of the transformer 105 (Piezo transformer) in 7 ,

The device 807 is used to determine the phase shift between the switch current and the load current from the detected quantities at the two inputs 8071 and 8073 issue. In this embodiment, the device 807 as a phase detector which is part of the phase locked loop 805 is. That of the phase detector 807 determined phase difference signal, which also depends with respect to its frequency dependence on whether an over-resonant or if there is a sub-resonant operation, is determined by the integrator device 809 , implemented in this embodiment as a filter consisting of a resistor and a capacitor, integrated. The filter output is at the input 81101 of the VCO 811 which, starting from the filter output signal, generates a suitable frequency f and an associated duty cycle D _f . This output signal is sent to the control input 1035 of the switch 103 forwarded. It should be noted at this point that the integrator device 809 , which is particularly inexpensive in this example, can also be implemented in other ways, such as by a suitably interconnected operational amplifier, or other time-delay circuit.

In this embodiment, the switch comprises 103 a voltage controlled circuit breaker 1037 , The output signal of the VCO 813 becomes the gate driver 813 whose output signal is relayed to a gate of, for example, a field stop IGBT or a MOSFET as possible embodiments of the voltage-controlled circuit breaker. In this embodiment, the device is 807 as a phase detector for detecting the phase difference and generating a difference signal. This has the advantage that for controlling the switch 103 the phase locked loop 805 can be used, which can be realized inexpensively.

The scheme after 8th works as follows: If the output load increases (smaller ohmic resistance), then it will be 5 set a smaller transmission ratio. At the same time, however, the phase angle φ _LT decreases in the over-resonant case, so that the voltage Up, which is present at the output of the device 809 is issued, increases. About the VCO 811 is time delayed by the filter 809 a greater frequency at the gate of the fieldstop IGBT, for example 1037 set, which causes a reduction of the transmitted power. This leads to the over-resonant characteristic 5 to a smaller transmission ratio ü. However, since the output load has a negative differential resistance when it is a gas discharge lamp (fluorescent lamp), the output voltage increases and the lamp current decreases disproportionately. Thus one arrives at a transfer characteristic above the previous characteristic 5 , so that by changing the output impedance again a larger phase angle φ _{LT is} set, as in 5 is also shown (dotted curve 507 ). As the phase angle increases, so will the phase difference voltage U _p again decrease, and the control comes to a static end value.

The same applies to changes in the input voltage: When the input voltage of the converter increases, the phase angle φ _LT decreases 6 , This is after 5a transmit a larger output power. The phase difference voltage U _p thereby increases again and increases with time delay over the device 809 the frequency f, so that accordingly 5a reduces the transmitted power. This in turn results in an increase of the phase angle φ _LT , so that the control comes to a standstill.

If, for some reason, the scheme is included in the subresonant operation ( 5 . 5a ), it would not work anymore. The VCO 811 Therefore, if necessary, has a device, not shown, to store the applied frequency at the time of ignition. In an embodiment of the piezotransformer according to the invention 105 be found the ignition frequency in überresonanten branch of the load curve in 3a , This ignition frequency is then targeted during control under load, or only one by the parameters of the piezotransformer 105 falls below the defined amount, so that even a disproportionate change in the phase voltage U _p to smaller values no frequency reduction in the subresonant operation permits. For this, the VCO 811 continue to have a device, not shown, to ensure a minimum, lower limit frequency in load operation, which ensures this behavior.

As already mentioned, the VCO stands out 811 further by a duty cycle D _f , which is adjustable. To the operation of the oscillator 811 Explaining it will be over again 4 returned. The class E amplifier according to the invention is operated so that the switch is switched on after the switch voltage has become zero, possibly with a time delay. This results in turn-on times of typically DE = 0.25 ... 0.45, in order to achieve an optimal limitation of the switch voltage. These switch-on times are erfindungsge according to the voltage-controlled oscillator 811 supplied in such a way that the current in the switch during the on-time is only increasing, as shown in 4 is illustrated by the course of I _S in an interval marked by t _on . The VCO 811 is therefore designed so that it provides a duty cycle D _f necessary for this purpose. This can be done, for example, by an in 8th not shown means for setting a predetermined duty cycle of the output signal of the oscillator 811 will be realized.

Out the above-described embodiments according to the present invention Invention will be apparent that the Improvements over the Prior art mean that a resonant inverter, consisting of a self-excited or an externally excited one amplifier Class E, with a tuned to resonant frequency mode of operation a high frequency using an electromechanical Energy converter with high load circuit quality, high efficiency and a limited load change and allows a limited input voltage swing by a dynamically fast switch with at least about three times Reverse voltage opposite the maximum input DC voltage is used. Because only one switch and a relatively simple drive circuit are required, can be the circuit as a one-chip solution (eg in a SMART POWER technology) realize, or in a known cost-effective multi-chip design without a need for bridge-capable high-voltage technology for the Drive circuit. Using, for example, conventional High-voltage circuit-breakers (eg Fieldstop IGBT up to 1700V, Cool-MOS bis 800V), operation at rectified mains voltage is possible. The needed Drive circuit operates in particular when using MOS transistors or fast IGBT because of the capacitive gate behavior very low loss, as well as the switch and the electromechanical transducer. By the Use of MOS switches or even fast IGBT is high Switching speed achievable. Because of the resulting possible rate increase up to about 200 kHz or more, the capacitive ones are decreasing and the inductive components of the overall arrangement, such as the input choke. A resonance inductance is therefore no longer necessary as well as a high-side driver device, which is comparable Half bridge solutions with narrowband energy converters are not, or only with restrictions in terms of the driving accuracy, is given. In addition, in the load circuit no reactive components (capacitors, inductors) are required and become Completely replaced by the piezoelectric transformer.

Opposite one elaborate evaluation of the load current to adjust the rated power to Font (3) is for the chosen one Class E circuit only one phase comparison between the zero crossings of Load current and switch current required to set the rated power. This simplifies the control circuit and can be integrate as analog circuit on a smaller chip area than if consuming Evaluation circuits for the amplitude of the load current would be used, or this evaluation through costly bridge driver ICs is made.

The inverse voltage transfer ratio 1 / ü (input voltage / output voltage) of the electromechanical transducer is relative to a sine wave transmission at resonant frequency in adaptation to typical mains applications for discharge lamps (For example, low-pressure lamps) according to the invention with 1.5: 1 to 5: 1 selected. there For example, the input line voltage may be between 80 and 260, for example Volt AC voltage. From the electrical filter behavior of the electronic mechanical transducer (eg piezoelectric transformer) then results in a load voltage (burning voltage) in the typical Range of low-pressure discharge lamps of z. B. 50 to 160 V. For other gear ratios would be in this circuit topology a load adjustment with optimal switch voltage limiting for the can not be reached, which is why the correctly dimensioned transmission ratio in Rated load operation is an essential basic idea of the solution according to the invention.

Farther is the input capacity of the electromechanical transducer to be chosen so that in addition to the parallel to the Converter input switched semiconductor switch no further parallel capacitance is needed. The value of this input capacity is at a frequency of typically 100 kHz and power from 10 to 20 watts depending on the input voltage between 100 pF and 1 nF. At low input voltage (80 to 160 V AC) is the value of the capacity to choose about 500 pF to 1 nF, at a big one Input voltage (160 to 260 V AC), this value is about with 100 pF to 500 pF to choose.

The parallel acting capacity of the switch is on the order of less than 200 pF. For other power ranges, the value of the input capacitance shifts up (higher power) or down (smaller power). Such an adaptation is possible by a construction of a piezoelectric transformer. Preferably, a circular or a laterally oscillating piezoelectric transformer is used here. On the other hand, a piezoelectric transformer which operates on the basis of a thickness vibration or a Rosen type transformer is we niger suitable for this application, since they do not allow a corresponding transformation ratio in the specified power range and the required input capacitance at a sufficient efficiency. It should be noted, however, that these two types of piezotransformers can be used according to the invention.

It also helps the negative differential resistance of a gas discharge lamp in the burning mode, to stabilize the class E zero-voltage circuit, and is used as a load in conjunction with a narrowband electromechanical Converter better suited as a constant ohmic resistance. For this purpose, the piezoelectric transformer is designed so that its Voltage transfer function has a sufficient bandwidth, which, as already mentioned is, re the frequency follows approximately a Gaussian function, and chosen so broadly will that at a deviation from the resonance frequency, a reduction of the Voltage transfer ratio ü occurs, counteracts the increase in the voltage at the gas discharge lamp. This can be done a control or regulation for Gas discharge lamps over a detection of the lamp current technically reliable implement the frequency bandwidth until waste to half a performance at least about 5 to 10% the nominal frequency is. In this area, and by the effect of output capacity at a rising Lamp voltage, changes the behavior of the class E circuit with respect to the zero voltage circuit and the switch current load hardly, so that no significant changes in the Switch maximum current, the switch reverse current and the switch maximum voltage occur at approximately constant relative on-time. This is due to the fact that the Output capacity of the piezoelectric transformer is large enough (e.g., a few nanofarads), to record enough reactive power even in the load-free state, and resonantly fed back to the entrance, when the load opposite their nominal value is smaller.

Of the Class E converter responds to an amplified capacitive or a less ohmic output load with an increase of the reactive current component, without that Zero voltage condition is violated. In this case, the inherent output capacitance of the piezoelectric effect Transformers in this sense stabilizing. Thus, the returns Switch voltage continues to return to zero, even if the gas discharge lamp has been extinguished or removed. This increases only the reverse current component in the switch. In the event that no Active power is transferred to the load more the maximum reverse current is equal to the maximum inrush current of the switch (ignition mode). Consequently can detect end-of-life effects or load circuit interruption by sampling the reverse current in the switch, without that monitors the lamp voltage must become. However, changes the optimum relative on-time with the frequency and must at larger frequency changes tracked within the bandwidth become. Such is for a fixed point load within a PLL control, however, less often or not at all and will only be in a performance position in a larger area be applied, or if an ignition operation is provided with preheating the gas discharge lamp. Because of the greater losses while preheating in the piezoelectric transformer is a preheater-free Instant start for this solution however, to be preferred.

at a fluctuation of the input voltage changes the transformation ratio of the electromechanical Converter little, so that the Power approximately with the square of the input voltage changes. Becomes the input DC voltage of the converter decreases, so the sink Active current and the reactive current in the load circuit accordingly, and the switch reverse current decreases. When the reverse voltage reserve the switch is big, can the input capacity of the piezoelectric transformer are reduced to a Zero voltage switching (ZVS) up to smaller input voltages to reach. Is the reverse voltage reserve of the switch, however small, so the input voltage must not be below a certain Minimum value decrease. This value is due to the sufficiently large output capacity of a piezoelectric transformer with decreasing ohmic load but small enough to the usual To balance voltage fluctuations of the networks and in addition to a greater voltage fluctuation at the input charging capacitor. If the load is removed or is the load-side gas discharge lamp unlit, so causes the constant or slightly increasing capacitive Output load of the piezoelectric transformer on the one hand a Maintaining the zero voltage switching by the rising Reactive current component compensates for the missing load current component. on the other hand However, the switch maximum voltage is not much larger because the effective input current decreases and of a smaller proportion of the load current must be compensated, whereby the total relative Switch-on time remains constant.

If the resistive load increases, the proportion of reactive current decreases to smaller values so that the maximum switch voltage is not exceeded even in this case. If the ohmic load is too large, the zero-voltage behavior would no longer be achieved because the transfer characteristic of the piezoelectric transducer only allows a limited power transmission (maximum load). A load increase encounters the same limitation in performance transmission as an input voltage increase after 5a , Thus, the additional power consumed on the switch is converted to heat when it must be turned on at a voltage greater than zero. Thus, the switch maximum voltage is also not exceeded by the transmitted power is no longer increased. In the event that too much load is used, this can be detected by detecting the voltage return to the switch, so that an overload of the switch can be avoided by the converter is turned off. Thus, one can use as a switch, a component whose maximum permitted voltage in any possible operating state of a gas discharge lamp with electromechanical transducer (piezoelectric transformer) is exceeded. Therefore, a non-avalanche-proof switch (MOSFET or IGBT) is well suited for this application, since the output capacitance of the converter, which acts on the input, has a compensating effect with decreasing resistive load, and a maximum transmittable power can not be exceeded. These properties are usually given by the use of inventively dimensioned piezoelectric transformers.

By the use of non-avalanche-resistant components, in particular Fieldstop IGBT as a switch, the present application becomes more cost effective, by no protection against overvoltages must be used on the switch, since the output circuit the Protection of the switch by its electromechanical and thus electrical Features already guaranteed.

As it already mentioned can be, one can to a control and regulation of such a structure Converter the phase angle between load current and switch current evaluate. The switch current is only by the DC component of Input choke superimposed, which changes the phase shift by a fixed amount, and therefore not or only slightly depending on the power or input voltage. If the input choke of the converter is chosen so small that the inductor current can decay to zero or become less than zero, so you can the proportion of the superimposed Reduce direct current from the throttle or almost to zero because then the inductor current is typically in the When the switch is turned on, it reaches approximately zero crossing. Even if the input choke is larger, is a phase detection for power control possible and has little be adapted to the respective value of the input throttle, because the effective input current in this application is much smaller than the load current is.

Also the fluctuation of the input voltage can be via the phase detection and a corresponding frequency change compensate, as the capacitive component of the output current in the converter increases when, due to decreasing input voltage, the active power gets smaller.

If If the input voltage is too low, the target transformation ratio will be added Rated frequency not reached when the load impedance due to negative differential resistance of a gas discharge lamp gets big. The electromechanical transducer usually has the property at a decreasing input voltage one with this square transmit decreasing power.

If On the other hand, the ohmic output impedance is greater, the converter only with an increase the output voltage will respond, even if a small input voltage is applied. This shifts the transformation ratio larger values and the internal transformer losses increase slightly. At the same time, however, the inherent output capacity of the converter with a larger voltage applied, whereby the capacitive current component increases and the ohmic current component decreases. The magnification of the transformation ratio can be adjusted by a design of electromechanical transducer be that the Output voltage from maximum load (minimum possible load resistance) to smaller loads (greater load resistance) increases so that the resulting equivalent resistance with respect to the input about constant stays or changes little.

Thereby The class E converter can operate at a variable load in a wide range Input voltage range can be operated without the zero voltage condition is violated and by the transferred Performance can only be varied by small frequency changes. It is therefore also possible the phase angle between load and switch current approximately constant to hold and thereby both changes the input voltage as well as changes balance the output load while maintaining the ZVS condition. This possibility is at a transformer with constant parameters, especially with constant gear ratio, not in such a wide range of load and input voltage change given.

The size of the input choke can also be used to adjust the power within certain limits at a given frequency. If the input choke is made larger, the transmission power increases by the same frequency due to the electrical characteristics of the class E converter, the effective stored energy increases in the input throttle, which at the Load circuit is passed on. The adjustment of the power through the input inductor, however, is possible only within smaller limits because of the limited bandwidth of the electromechanical transducer and will affect the overall performance insignificantly within the usual tolerances of inductive components. On the other hand, the adjustment of the input choke can be used to adjust the operating point, if another adjustment should not be made. An advantage of the finite design of the input choke is thus the possi bility to balance the lamp power. If the input choke is made too large, it can cause an improved smoothing of the current harmonics to the network (noise voltage), but also causes a necessary adjustment of the input capacitance of the converter to smaller values at a power increase and at a constant transformation ratio or a smaller step-down ratio and more consistent or larger input capacitance of the converter.

For the typical Downward transformation ratio of 1.5: 1 to 5: 1 in a nominal load operation and in the other mentioned electrical data are those required for a typical invention implementation Values for the input choke at a typical frequency of 100 kHz between 3 mH and 20 mH.

to Setting the respective desired nominal power is in time after the detection of the ignition PLL control loop in Operation set in which the zero crossings of switch and load current sampled and passed on to a phase detector. Farther This phase difference is passed to a filter which has a smoothed Output voltage generated. This is done on a suitable VCO (voltage controlled Oscillator), which adjusted to a desired value should be (setpoint comparison) and having a suitable gain. The output of the VCO is a frequency signal with associated duty cycle according to the invention (constant or slightly variable within the stated range) via a driver to the switch (Gate of an IGBT or MOSFET) returned. This may be the duty cycle with decreasing frequency slightly increase and with increasing frequency slightly decrease or it is kept constant.

at In the preferred embodiment described above, the phase difference signal becomes positive connected, whereby an approximately constant power is generated. If a gas discharge lamp e.g. due to aging a larger burning voltage owns, then flows a disproportionate smaller lamp current, what as load change (load reduction) can be designated. In the process, however, the converter becomes the power keep it constant by first "determining" that the phase angle is due to sinking active load has become larger is. The resulting phase voltage Up is according to the diagram but thus become smaller. If it is given positive to the VCO, then the frequency drops slightly and the performance is increased again. Thereby the phase angle decreases again, and the phase difference voltage decreases rises again according to diagram. Thus, the regulation comes at some point a new actual value of the lamp power, but not very strong deviates from the initial value. So it's a regulation that is only 100% exactly, if you could adjust the parameters so that the gains of the VCO, the phase difference voltage formation, and the controlled system even (class E with piezo transformer), complete compensation of the power change would allow. This is not the case in practice, but with a tolerance the power of +/- 10 up to 15% is quite acceptable. At the input voltage is it is similar. If this increases, increases the power at the same frequency. This decreases the phase angle decreases, and the phase difference voltage increases. In order to but it will also be a bigger one Frequency adjusted, bringing you over the controlled system (esp. By transmission curve of the piezoelectric transformer) again sets a smaller transmission ratio. Thus, the performance decreases again, and again you expect, that fluctuations in performance occur as part of the input voltage changes be kept within small limits, since the scheme is also not completely accurate is

Claims (19)

Resonant converter for driving variable loads, comprising: a piezo transformer ( 105 ) having an input port and an output port for providing an output signal for driving the variable load ( 107 ); a switch ( 103 ) for providing an input signal from a source ( 101 ) to the input gate of the transformer ( 105 ); an input choke ( 201 ), which between the source ( 101 ) and parallel to the input gate of the piezotransformer ( 105 ) arranged switches ( 103 ) is switched; a control device ( 109 ) for controlling a switching frequency of the switch; the piezo transformer ( 105 ) is dimensioned and connected in such a way that when a rated power is supplied to the variable load ( 107 ), a voltage transformation ratio between input signal and output signal of 1.5: 1 to 5: 1; and wherein the control device ( 109 ) for controlling the switching frequency of the switch ( 103 ) based on a phase shift between a switch current and a load current at variable Load and / or variable input voltage is designed. Resonance converter according to claim 1, wherein an input capacitance of the piezotransformer ( 105 ) is fixed depending on the size of the input voltage and the rated output power. Resonant converter according to Claim 2, in which the input capacitance of the piezo transformer ( 105 ) is set to a value between 100 pF and 1 nF. A resonant converter according to claim 2 or 3, wherein the input voltage is between 80 and 160 volts and the input capacitance of the piezotransformer ( 105 ) is between 500 pF and 1 nF. Resonance converter according to claim 2 or 3, wherein the input voltage is between 160 and 260 volts and the input capacitance of the piezo transformer ( 105 ) is between 100 pF and 500 pF. Resonant converter according to one of Claims 1 to 5, in which the inductance of the input choke ( 201 ) has a value of 3 mH to 20 mH. Resonant converter according to one of Claims 1 to 6, in which the switch ( 103 ) a voltage-controlled circuit breaker ( 1037 ), which may be implemented as a field stop IGBT or as a cool MOS transistor, having a first input, a second input and a control input to which a control signal can be applied comprises. Resonant converter according to claim 7, wherein between the second input and the first input of the voltage-controlled circuit breaker, an antiparallel diode ( 1039 ) is switched. Resonant converter according to one of claims 1 to 8, wherein the control device ( 109 ) means for detecting ( 801 ) dependent on the switch current size, means ( 803 ) for detecting a variable dependent on the load current and a device ( 807 ) for detecting the phase shift between the switch current and the load current from the detected quantities. Resonant converter according to Claim 9, in which the control device ( 109 ) a phase locked loop ( 805 ) for controlling a mean phase shift to a constant desired value. Resonant converter according to Claim 9 or 10, in which the control device ( 109 ) an oscillator ( 811 ) whose frequency can be set as a function of the determined phase shift and whose output signal for controlling the switch ( 103 ) is included. Resonant converter according to claim 11, further comprising means for setting a predetermined duty cycle of the output signal of the oscillator ( 811 ) having. Resonance converter according to one of claims 1 to 12, in which the variable Load includes a gas discharge lamp. Method for driving variable loads by means of a resonant converter comprising a piezotransformer ( 105 ) with an input gate, wherein the piezotransformer ( 105 ) is dimensioned such that upon delivery of a rated power to the variable load ( 107 ) the voltage transformation ratio between input signal and output signal is from 1.5: 1 to 5: 1, which further comprises an input throttle ( 201 ) between a source ( 101 ) and one parallel to the input gate of the piezotransformer ( 105 ) arranged switches ( 103 ), and a control device ( 109 ), comprising the following steps: controlling a switching frequency of the switch ( 103 ) by the control device ( 109 ) based on a phase shift between a switch current and a load current at variable load and / or variable input voltage to provide an input signal to the input port of the piezotransformer ( 105 ) and thereby generate an output signal for driving the variable load. Method according to claim 14, with the following steps: Detecting one of the switch currents dependent size; To capture one dependent on the load current Size; Determine the phase shift between the switch current and the load current from the recorded sizes. Method according to claim 15, comprising a step of regulating an average phase shift to a nominal value using a phase locked loop ( 805 ). Method according to claim 16, comprising the following steps: controlling a voltage-controlled oscillator ( 811 ) based on the mean phase shift; and using the output signal of the oscillator as a control signal for the switch ( 103 ). A method according to claim 17, comprising a step of setting a predetermined duty cycle of the output signal of said oscillator ( 811 ). Method according to one the claims 14 to 18, in which as changeable Load a gas discharge lamp is used.