TWI228944B - Self-oscillating electronic discharge lamp ballast with dimming control - Google Patents

Abstract

The present invention provides an electronic ballast circuit comprising: an inverter electrically connected to a DC power source, so as to switch the DC power source for outputting an AC power source; a resonant matching circuit comprising an inductor, a capacitor and a transformer, so as to form a resonant circuit. The current of the resonant circuit is fed back to drive the gate terminal of the inverter, and the inverter is electrically connected to a load through the resonant matching circuit.

Description

1228944

Di-D4: Zener diode

Dst: Diode

Np: winding

Nsl: winding

Ri: resistance

Rgl: Gate resistance VB: DC voltage

Dac: Gate fluid Lm: Excitation inductance Q1, Q2: Transistor ns2: Winding R2: Resistor Rg2: Gate resistance VetH: Xibu Department voltage source 柒 If there is a chemical formula in this case, please disclose the chemical formula that best shows the characteristics of the invention:事项 、 Declaration items □ This case is the first paragraph of Article 20 of the Patent Law □ The period specified in paragraph 1 or paragraph 2 of the proviso, the date is: _ 玖 Description of the invention (the description of the invention shall state: (Technical field, prior art, content, implementation, and drawings are simply explained) Technical field to which the invention belongs The present invention is a self-excited power supply with adjustable power control, especially a self-excited type with dimming control Electronic ballast for discharge lamps. φ Previous technology The white light source of the gas discharge tube is a fluorescent tube as an example. The increase in efficiency has always been the focus of research and development in this technical field. The light source of such a gas discharge lamp generally generates less heat and has a higher energy conversion efficiency. The overall efficiency of the gas discharge lamp can be increased by reducing heat consumption. However, the main issues discussed in the past were the control of the light spectrum and light source output of gas discharge lamps. However, since the efficiency gains of gas discharge tubes and fluorescent tubes are much larger than those of incandescent lamps, gas discharge tubes and fluorescent tubes have directly replaced incandescent 6 1228944 lamps in the market and manufacturing positions. = Complex than incandescent and gas discharge lamps; electronics are extremely complex and expensive. The heart σ and the control circuit are relatively more specific. 'Only traditional gas (magnetic banast) can be micro and wide-inductive ballasts are mainly used today; and the two-child safety, device system' has a small size, light weight, high Luminous efficiency, c-tone and other advantages. The main test of dimming or brightness and lighting system development is energy saving ... b Energy saving efficiency over 50¾. In commerce, whether you can provide the need for the environment to control the size of the light source, and increase the self-needle m. For example, it can be used to reduce computer workstation production and visually increase the effect of objects and space characteristics. . Fortunately, fortunately, electronic ballasts are very expensive for dimming control. Ϊ́ and irm: mainly used to reduce the complexity of control as much as possible. However, the operation of the conventional self-excited circuit is based on natural characteristics and load factors, so its control is relatively difficult, and the sensitivity of the load, circuit components, and line voltage changes is very high. Variations in its original load, circuit components, and line voltage will cause the self-excited frequency to change, thus changing the power of the discharge lamp. For example, 'when the line voltage has a change in i', the power change rate of the discharge lamp is usually 纟 15%. Such changes will usually exceed the power limit of the ± 10% discharge lamp and shorten the life of the discharge lamp. Such problems are not limited to the control of discharge lamps, but they also occur: a power supply or a conventional converter configured in a self-excited circuit, including a buck converter (buck c0nvmer) and a boost converter Converter (boost C0nverter), buck-boost converter (buck b〇⑹ converter), flyback converter (F 丨 yback c〇nverter), and forward 1228944 converter (Forward C_erter), push Pud! Converter, symmetric or asymmetric half-bridge conversion circuit and full-bridge conversion circuit. Another complex factor is the peak current factor (CF) of the discharge lamp current, which is the value of the peak current and the root mean square value of the discharge lamp current. For high-frequency electronic ballasts (ba 丨 丨 buckle), the current peak quality factor is reviewed (1 faCt ° r, CF) is an important factor in the design of electronic ballasts: In general, the higher the current quality factor, the more discharge lamps The shorter the life span. For unsaturated pure sine wave signals, the current peak quality factor is 4 and the triangular wave current peak quality factor is 1.7. Many electronic ballasts are “Charge-pump-power_fact〇rc〇rrecti〇n,” the ballast state is like electricity and pump power factor correction. 7 gates ', and its, ^, (over · 7. Therefore, frequency modulation is the most commonly used to ^ current peak quality factor', although the difficulties encountered. As stated above ... used for professional purposes, the present invention Familiar with the idea of knowing the technology, he invented the "self-excited dog put" and improved invention control. "Purpose, the electronic ballast dimming of discharge type discharge lamp SUMMARY OF THE INVENTION The object of the present invention is to provide an electronic power supply. Power supply, power converter: ° Early between the structure, ^ grid cheap lamp electronic stability cry original conversion benefits (connverter), or discharge current peak f S for a high efficiency and better discharge lamp two; 1 :) Electricity because of improving the circuit :: rate]: ^ in providing a high-efficiency technology and circuit one, 4 hands U prime (power fact0 0 using Di Gaiyou to identify 7C pieces to achieve frequency modulation + ^ one In order to reach the current peak quality factor of the 4 circuit "Electrical Safety of Discharge Lamps" and Conception'—A power supply such as a gas woman, includes a frequency converter (inVerter), a resonant 1228944 matching circuit (resonant matching circuit), and a conversion circuit (▲ erter circuit). The converter circuit is used to determine the switching frequency of the 2 忒 inverter, so that the switching frequency is essentially independent of the load of the power supply. The power supply is connected by the resonance matching circuit ( 1 ^ 〇 别 111 matching circuit) and the load coupling connection. This case can get a deeper understanding by the following diagrams and detailed description. The diagram briefly illustrates the block diagram; the first diagram is the preferred implementation of the case Example of the circuit of an electronic ballast system: ί ί ί The circuit diagram of the M0SFE D-driven self-excited electric ballast electronic ballast of the first preferred embodiment of the case: rgl 2. The simplified equivalent circuit and waveform schematic block diagram of the second diagram: the fourth diagram is the circuit diagram of the electronic ballast of the preferred embodiment of the case; the fifth diagram is the simplified equivalent circuit diagram of the fourth diagram; + question U仏 '5 cycles of equivalent current ^ (current transfomer) Coil voltage equivalent circuit diagram; rner) .. · Fruit circle The seventh diagram is the circuit diagram of the second stator of the case; the sixth figure is the sixth. The circuit diagram of the optimized implementation of Figure ；; the self-excited electronic electronic safety device of the preferred embodiment is shown in Figure 8. This is a good example / the soil is a good example of the circuit can be applied to this case protection circuit diagram The ninth diagram (a), (b), and (c) of the overcurrent protection are the schematic diagrams of the waveforms of the driving voltage of the pole; and the tenth diagram (a) (b), (c) of the gate-depressed switching current and gate ) Is a waveform diagram of depressor pressure in this case. SW and gate drive power 1228944 Symbol description 1 0 0 · Parent current power supply 1 1 0: Power factor correction AC / DC conversion circuit 120: DC connection capacitor 130: Inverter 140: Inductor 170: The discharge lamp 1 80 : Internal capacitor 2 1 0: Metal oxide semiconductor field effect transistor 2 11: Metal oxide semiconductor field effect transistor 212: High-frequency capacitor 214: Inductor 215: Capacitor 310: Power inverter 320: Resonant matching circuit 330: Gate switching Circuit 340: current sensor 400: pulse transformer 81 1: DC silicon controlled transistor (SCR) α: phase angle C 1, C 2: capacitance Θ: phase angle iinj · current iz: diode current i $ · feedback Current imag · Excitation current cst: Capacitance CT: Current transformer D1-D4 · Schneider diode Dae: Gate fluid Dst: Diode Lm: Excitation inductance Np: Winding Q1, Qz · Transistor Nsl: Winding Ns2: Winding 1: resistance R2: resistance Rgl: gate resistance Rg2: gate resistance VB: DC voltage Vctrl: external voltage source For implementation, please refer to the first figure, which is a circuit block of the electronic ballast system of the preferred embodiment of this case Illustration. As shown in the first figure, the electronic ballast system is 10 1228944

Included by '— father stream package source 1 〇 〇 / j £ dfl »JU Apprenticeship for the package. However, in general, the electronic amplifier or the nt supply circuit is powered by a DC power source. Therefore, the packaged child system needs to include a power factor corrected AC / DC (PFC AC / DC) conversion circuit 11o. The pFC ac / dc conversion circuit n0 has a power factor k positive and AC / DC conversion functions. . The electronic ballast circuit usually includes a DC link capacitor (DC Hnk plus or minus) 12 and is electrically connected to the PFC AC / DC conversion circuit 11. The power source of the discharge lamp used today is an AC current, so the electronic ballast circuit needs to include an inverter i30 and a series connected inductor 140. The inverter 130 converts one of the DC power switching outputs converted by the PFC AC / DC conversion circuit 110 into an approximate square wave voltage signal, and converts the approximate square wave voltage i into an approximate sine wave signal through the electricity 140. . The inductor 40 and the internal capacitor 180 of the discharge lamp 170 form an LC or LCC resonance matching circuit to reduce electromagnetic noise interference (reading), which is used to strengthen the waveform adjustment and extend the life of the discharge lamp. In such a circuit configuration, there are three most basic controllable parameters to control the power of the discharge lamp: (!), DC voltage (DC Hnk… V) (2), duty ratio (duty rati〇) D, (3) Switching frequency. When the fixed frequency and fixed duty cycle are controlled and the dimming control of the discharge lamp is determined from the current of the 5 bulbs: 3 electric lamps, the power of the discharge lamp is a function of the DC voltage vB. The DC voltage can be controlled by changing the DC voltage (Dc nnk v〇h_). The duty cycle is controlled by changing the on-time of the 6-frequency switch. When the switching period is fixed. The dimming control ^ is realized by controlling the duty cycle. When the on-time of the switch is reduced, the energy transferred from the power supply to the load will also be reduced. The frequency control changes the size of the switching frequency when the duty cycle is maintained at a certain value (that is, 50 ° /.). The dimming control implemented by frequency control changes the switching frequency different from the natural resonance frequency of the resonance circuit 140, so that less energy is coupled to the discharge lamp 1228944: the control methods described in the description can be combined and used separately, but it will cause the direct Α Voltage dimming control is generally less effective. There is no way to control the output voltage of the power factor correction stage. The duty cycle control system is a better dimming control. When the duty cycle is very small, there is no ^ voltage switching operation and can not tolerate the strict MOSFET body. 俨: Reverse 相关 related problem (reverse • ⑽very_related㈣ 二) The provincial self-excited converter is in forty-five It has been applied to the "two straight to two" and strong electronic ballasts years ago. The main advantages of self-excited converters are: the advantages of electronic: fixed Γ Λ ust) operation, especially in applications where it is lacking— This is the simplest, cheapest and most efficient circuit architecture. However, as mentioned earlier, the operating frequency of a self-excited resonant circuit = the frequency at which it operates, which depends on the load and is extremely difficult to control. The combination of the circuit structure and the frequency adjustment of the light control of the conventional specific circuit element is extremely complicated = the lighting efficiency of the discharge tube cannot be the optimal control.-For these reasons, the power control method Using reading magnetic music to change the switching frequency makes it easier to adjust the power of the discharge lamp. The structure of the light adjustment control circuit of the electric lamp body is very simple.

Take the shoulder test + the second and third pictures (a) and (b). The working principle of the self-excited converter is described as follows: The second picture is the first best I MOSFE: automatic self-excited electronic electronics in this case. The circuit of the stabilizer is shown as one of metal oxide semiconductor field effect transistors (MOSFETs) 21 ,,, and ^ = 2: device output-square wave voltage. The high-frequency capacitor 212 and the electric or 2 ″ 4 Ϊ Ϊ matching circuit to change the waveform of the output voltage signal, improve the starting voltage of Shida and stabilize the current of the discharge lamp when the steady state. Electric, 匕 is a blocking capacitor ( blocking capacitor) II with hysteresis and direct cooling: the voltage is directly across the inductor 214 ±. The self-excited driving circuit contains; 12 1228944

The current transformer CT has three windings Np, Rg2 and a back-connected diode (D4). The resonant inductor current is provided via this circuit. The starting circuit includes a resistor Ri and a gate fluid Dac. Among them VaS |, V The fluid CT is fed back and converted into a complementary voltage to drive the metal oxide half-efficiency transistor 2 1 0, 2 1 1. The initial gate pulse signal is generated by the starting resistors R 丨, R2. The capacitor Cst, the diodes vgsi, and Vgs2 respectively represent the voltage across the gate and source of the switching elements 210, 2 11. The second diagram (a) is a simplified equivalent circuit diagram of the second diagram. As shown in the third diagram U) No, the Ronby CT is modeled as a current-controlled current source in parallel with a magnetizing inductance Lm. An ideal transformer is coupled to the gate end of a two-metal oxide semiconductor field-effect transistor. See Figure 3 (b) for the first The simplified equivalent circuit waveform of the second figure is not intended. At any reference time, the metal oxide semiconductor field effect transistor 2 1 0 is worn, and the metal oxide semiconductor field effect transistor 2 is turned on. Therefore, the exciting current imag is lower than the feedback current.丨 s, so that the diode current iz is a positive value. Ideal zener diodes s The gate voltage applied to switch 21 〇 is a negative value, and the gate voltage applied to switch 2 η is a positive value, so that switch 2 丨 1 maintains conduction The switch 2 is maintained at a load. Because the winding current is a positive value, when the feedback current changes its state in the resonance state, as shown in the third figure (b), 220, 221, the exciting current increases linearly. Finally, in At time t1, the exciting current imag is higher than the feedback current is, so that the diode current becomes a negative value, which causes the diode voltage to change polarity, which causes the switch 2 1 1 to be disabled and the switch 2 丨 0 to be turned on. The next symmetry is turned on. Half cycle. In the figure, ip represents the current of the primary coil of the current transformer CT, and l represents the current of the secondary coil of the current transformer ct, where is =: ip / NN represents the turns ratio of the current transformer CT. As mentioned above, It can be seen that the relative magnitude of the exciting current imag and the feedback current is a key factor determining the operating frequency. Assume α is a phase angle between the exciting current imag and the feedback current is, and Θ is the inverter output current and 2 13 1228944 should be resonant Phase angle of current, aM./2)-e FIG two (b), and therefore (1) (2)

IpSinG / jvJ rz τ

One mag, t〇 = V7Ts / 4L, where IP, N, VZ are the resonance ratio and the acceptance voltage, respectively. The peak value of $ borrow_ + and the number of turns of the current transformer C are up to $, and the monthly pressure drop across the back diode. With it increased. With the excitation percentage of bran, the slope of the exciting current will be…, the exciting current and the zener, and the dead θ period will be complementary Q + U ρ W 疋, so the switching Zhou Gongzhu θ shortens and the switching frequency will respond In addition, the main effect of combining switching frequencies is B ^ I, and there is an effect when the load changes. Consider inductance formula 3

Lm = μΑ ^ ρ2 / le (3) There are two: change the dagger, and le is the magnetic permeability of the core, the effective wearing surface and the length after the effective magnetic path. NP = UeV2Ts Ns / (μΑ0) 2 (4 lpsin Θ)) 1 3 ⑷ Therefore, it is very straightforward to simplify the design steps of the circuit. The typical design f is designed for the given bus voltage and switching frequency, the size of the resonant element ^ 14 and 2 丨 1. Therefore, the resonance current 1P and the phase θ can be set at the rated discharge lamp power. From the selection of the iron core and the magnetic flux density B〇ρ, the number of turns of the secondary coil of the current transformer is:

Ns-VxTs / 2AeBop (5) where the number of turns of the primary coil can be calculated according to equation (4). The above analysis and design are based on a simplified model. For a more detailed analysis, please refer to the paper by Tao et al. A Self-Oscillating Drive for Single-Stage Charge-Pump Power-Factor-Correction Electronic Ballast with Frequency Modulation ", Industry Applications Conference , 2 000; Conference Record of the IEEE, Volume 5, 2000; pp.3367-3373. However, as shown in the fourth figure, according to the simplified model, the self-excited resonance circuit 1228944 can be regarded as a system, which is Bayi 31 〇 provides a square wave voltage signal 3 ^ solid subsystem: a power inverter, the square wave voltage signal is _::?? Zhenba with circuit 320 series conversion 330 conversion by voltage or current sensing nu and-gate conversion The circuit or current is-the proper drive ° = the detected feedback voltage body. These three subsystems form the switching transistor of the inverter and are essentially dependent on the load: = The car system is determined by the parameters of the circuit and is It is necessary to achieve the frequency control loop of the soil. A better method is to capture the control voltage and enter the independent stable paper. As before, // Go: Go 'is disclosed at the Tao frequency. As a result, when the injection current is wound, the switching technology has successfully improved the circuit efficiency and thus reduced. -〇0, line current spectral wave value (linecu ent = • ㈣factor (― 田 备 nv harm〇nicS), The current peak factor (lamp erest fact () r) and the sensitivity of the discharge lamp power to line voltage changes. The only disadvantage is the current deviation injected into the current transformer. The technical issues to overcome the self-excited frequency change are discussed below: see The fifth diagram is a simplified equivalent circuit diagram of the fourth diagram. As described above, the polarity of the zener diode current ιζ determines the polarity of the gate drive voltage. Therefore, the zener diode current iz is changed. The polarity changes the switching frequency. The diode current 丨 z is the difference between the feedback current and the exciting current, as shown in the following formula. {Ζ — is-imag = (ip / N)-Imag (6) From the above formula It can be known that a proper feedback current can obtain better performance. As shown by the dotted line in the fifth figure, a controllable current is injected to modulate the zero-crossing point of the diode current ^. Field current Control the audit diode current 1 z. However, 'the switching frequency is adjustable 15 1228944 The range of the change is limited. Changing the current span of the current transformer can effectively control the change of the exciting current. Fortunately, the current transformer branch line The coil voltage is determined by the second circuit. Therefore, according to the present case, the control audit diode current ^ is used to control the exciting current. As shown in the sixth figure, a voltage source with controllable voltage replaces the zener diode as the load of the current transformer CT. Unlike Zener diode clamping, the cross voltage of the CT coil of the current transformer is controlled by an external voltage source Vc ..., of which the pulse transformer 400 series provides C isolation protection for the driving voltage of the two gates. As shown in the sixth figure (b), a voltage source with controllable voltage includes a capacitor c ,, c2 voltage divider. The seventh diagram is a circuit diagram of the self-excited electronic electronic ballast which is the best example in this second example. The off-pass Γ-excited circuit 'question pole drive circuit and current transformer are divided into small signal transistors Q ,, q2 are used to amplify the gate base-collector junction transistor to borrow electricity ... The voltage is equal to the clamping capacitor voltage plus The upper base-collector is connected to the breadth to clamp the capacitor voltage and the two discharge resistors Rl and R from the outside. "-Voltage vctr 丨 The voltage is controlled. The switching frequency can be controlled at a voltage of 5 to 15 volts at the seventh stage. Consider the MoSFET gate limit ^ ^ f: 11 " 0 " Power dimming can be controlled by voltage The modulation comes from & the load is smooth and continuous as shown in Figure 4 and Figure 1. The noteworthy current injection makes simple and independent DC power supply: power and external control voltage source can be-Figure 7 The other way of the circuit diagram is to increase the lamp's life. The beauty, the advantage is that it can provide a better start. There are two steps. One is the "better start mode. In general, it is the lamp edge type of the heating lamp." —Is the start-up mode. Before the minimum voltage of the preheating mode discharge, at ^ ^ to an appropriate temperature, when the gas dynamic mode is reached, it is the heating camp and the lamp is blackened. The state of the enemy's electricity in the milk. However, this method is implemented by the 16 1228944 preheater. According to the present invention, the preheating switching frequency. 22:-Initially control the high voltage to achieve the expected to achieve sufficient preheating :: Change frequency in general-within seconds Capacitor (Rc) circuit. The time control can be achieved by-simple resistance of the lamp voltage to make the lamp = preheat switching frequency, so you do not need to use the circuit to protect the circuit Provided in the design of this case-one of the preferred embodiments of the case; normal operating conditions. The eighth figure is a schematic diagram of the circuit when the circuit detects the resonance port. :: Γ Once the overcurrent occurs, the two-to-two power converter does not It will be triggered. The path "scR) 8 丨 丨 ¥ is turned on, so that the ninth and tenth pictures of the electricity are based on the volt, Lr = .56mH, c_5: 2, and the seven-slot hair diagram is at a core voltage of 300 直流.丄 Single · 6 :? conditions and applications-industrial TDK side coil and 45 watts: ::: one primary side coil with 75 E secondary and 2N2907A, crystal U t standard plus 222a double L η Du Xintun Based on the results of the son-in-law experiment. ^ ㈤, the tenth picture is at full load, 70% load 60. / The switching current under the same voltage, the drive voltage of the interrogator and the corresponding control voltage under the tc are not llv, W4V-= 159.2¾, and the relationship between the frequency is a non-linear relationship, and the frequency is increased ^ Value, the power of the discharge lamp will drop rapidly. According to the above-specification, based on the above, this case can provide a simple electronic which provides-simple dimming control technology of discharge lamp: ’or power converter. Focus on all kinds of power supplies. Bie Jiaming seeks to protect the target. 17

Claims (1)

1228944 Scope of patent application 1. A power supply device, including: side frequency converter, electrical connection _ DC power supply, the a source is switched to output-AC power supply: and Chu Huan straight-resonant matching circuit, including at least one piano, Xiqiu according to sense, a capacitor and a variable pressure U matching circuit receive the AC power, the inverter's gate extreme, feedback, and drive to control the load through the Qiu according to PI control, where the inverter The load is electrically connected by the resonance matching circuit. 2 " The power supply device described in item 1 of Qishen II, where the power supply rectifies the parent current / DC conversion circuit to provide the DC power supply. 3 · If the scope of the patent application, the first device is provided in the initial stage of startup One high frequency two :: for · 1 Λ ^ 1 Jp '^ ^ ^ 1 ^ ϋ ^ t ^ ^ ^ ^ Switching frequency ... Including-controllable electric power to determine the frequency converter 5 · If item 4 of the scope of patent application The system voltage source includes a capacitor, eight wish π Γ, and a power supply, wherein the controllable voltage is 6. The patentable Capacitor (Capac Hill ve voltage divider). τ is called Gansu's Gansu power supply as described in the first item of the patent robe circuit: the pole drive circuit controls the transformer with two magnetic responses, of which the switching frequency of the w inverter. / Magnetic I ^ to control this: • The electrical tracer source as described in item 5 of the scope of patent application controls the transformer excitation +, and the controllable switching frequency. To control the frequency of the inverter, such as the patent application scope g 1 jg office + power supply even more than the power supply described in Bayi, where # + 9 dagger 3 an overcurrent protection circuit. . Hai Power • Electronic ballast circuit, including ... Source switching 'electrical connection DC power' This inverter will replace the old with AC-AC power; Wen Xu Yi will 5 Hai DC 1228944 a resonance matching circuit, including at least- In the Thai device, the resonance matching circuit receives the cross-inductance, -capacitance, and -transforms the inverter's gate terminal, which: the current is fed back to drive the load to be electrically connected. In order to pass the resonance matching circuit 10, the power supply as described in item 9 of Shenqiao's patent scope further includes an AC / DC converter: the original power supply, in which the voltage of the power supply. Used to provide the DC power supply. For example, the patent application 91 stomacher is provided at the initial stage of startup-high frequency switching employment supplier, where the frequency converter 12. The open-pole drive circuit as described in item 9 of the scope of the patent application includes a -An original supply, wherein the frequency converter switches frequencies. J ^ source to determine the frequency converter 13 · If the patent application scope of the 12th control voltage trace # ^ ^ ^ < child source supplier, which can be w!屌 includes a capacitor divider). ^ v capacitive voltage 1 4 · If the item 9 of the scope of the patent application, the gate driver of the device π π ’is the source of the source, in which the switching frequency of the frequency converter.堃 Jie's excitation current is used to control the U. For example, the scope of patent application No. 3 Control voltage source is to control the variable ink writing supplier, among which the switchable frequency. ^ Excit the magnetic pen k to control the frequency converter. 16. As described in item 9 of the scope of patent application, 1 f & person ^, a private power supply, wherein the power supply includes an overcurrent protection circuit. 17. A high-frequency switching frequency power supply for rubbing is similar to two% of a white private man — a control method that should include an electric power via: steps of a remote control method to control one of the power supplies σ ^ ~ N έ The frequency of excitation of the transformer μ in the frequency state to control the switching frequency of the inverter; and via a resonance circuit, the current feedback of the vibration circuit drives the transformer 19 1228944 frequency converter And the inverter is electrically connected to a load via the resonance matching circuit. 18. The control method as described in item 17 of the scope of patent application, wherein the load is a discharge lamp, and the control method is to control the illumination of the discharge lamp. 19. The control method according to item 18 of the scope of patent application, wherein the control method further comprises a step of controlling a DC voltage of the frequency converter. 20