Abstract:
An electronic controller for a high-power gas discharging lamp bulb includes a filter circuit to reduce interference and control the electromagnetic characteristics of an input power signal. A rectifier circuit electrically communicates with the filter circuit to generate a DC power signal. A power factor switching circuit electrically communicates with the rectifier circuit to increase the power factor and to stabilize the voltage and current of the power signal. A driver inversion and power control circuit electrically communicates with the power factor switching circuit to adjust to loading of the controller. An initiation trigger protective circuit electrically communicates with the driver inversion and power control circuit to control the timing of passing a trigger voltage to the lamp. An output matching circuit electrically communicates with the initiation trigger protective circuit to match the impedance of the lamp bulb connected to the output matching circuit.

Description:
RELATED APPLICATIONS 
   This application is a continuation of International Application No. PCT/CN 2004/000349, filed Apr. 14, 2004, which claims benefit of Chinese Patent Application No. CN 200410016366.4, filed Feb. 17, 2004. 

   COPYRIGHT NOTICE 
   © 2006 Fanglu Lou. A portion of the disclosure of this patent document contains material that is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure, as it appears in the Patent and Trademark Office patent file or records, but otherwise reserves all copyright rights whatsoever. 37 CFR § 1.71(d). 
   TECHNICAL FIELD 
   The present disclosure relates to a controller device for illuminating a high-power gas discharging lamp. More specifically, the controller controls high-power gas discharging tubes comprising dysprosium, indium selenide, natrium, metal halide bulb, and/or controls cold cathode luminous tubes. 
   BACKGROUND OF THE DISCLOSURE 
   The rating voltage of a gas discharging lamp is generally 80V-150V, but the current voltage supply is 220V. For proper use, one should decrease the current supply from 220V to about 80V-150V. Simultaneously, the bulb is provided with a step down, current limiting, and protective device of equivalent power. An inductive, low frequency choke is the most commonly adopted for these purposes. Such a low frequency choke occupies a large volume and is heavy. It also exhibits high loss, low power factor, high noise and strong interference, and low illumination quality; and its voltage, current, and power are difficult to control. 
   Chinese Patent No. 98218196.5 teaches an adaptive controller for a high intensity gas discharging lamp, which achieves light changes by adjusting inductance coil and inductive capacity. Like conventional inductance performance in regards to energy consumption, noise, power factor, voltage, current, and start-up, the adaptive controller consumes large amounts of energy and exhibits strong interference, and its power, voltage, and current are likely to be affected by circuitry voltage fluctuation. Therefore, the adaptive controller is not generally well-suited for application in a high-power gas discharging lamp. 
   Chinese Patent No. 01264335.1 teaches, however, a high power-factor electronic ballast for controlling a high-power gas discharging lamp, which provides an electronic ballast that can increase the power factor of the discharging lamp and is, therefore, energy saving and low-cost. Such an electronic ballast provides high quality lighting, and has a long service life, but does not work effectively if the power of the lamp is high. Because of the insufficiency of the pulse time and pulse amplitude, if there is exterior voltage fluctuation, the lamp is difficult to start up, or even be lighted. In the absence of a high-power, start-up trigger lighting circuit, the electronic ballast is not suitable for use in a high-power gas discharging lamp because of its poor stability and low reliability. 
   SUMMARY OF THE DISCLOSURE 
   Various embodiments described herein are directed to systems and methods for control of a high-power gas discharging lamp. According to one embodiment, an electronic controller for a high-power gas discharging lamp bulb includes a filter circuit to reduce interference and control the electromagnetic characteristics of an input power signal. A rectifier circuit electrically communicates with the filter circuit to generate a DC power signal. A power factor switching circuit electrically communicates with the rectifier circuit to increase the power factor and to stabilize the voltage and current of the power signal. A driver inversion and power control circuit electrically communicates with the power factor switching circuit to adjust to loading of the controller. An initiation trigger protective circuit electrically communicates with the driver inversion and power control circuit to control the timing of passing a trigger voltage to the lamp. An output matching circuit electrically communicates with the initiation trigger protective circuit to impedance match the lamp bulb connected to the output matching circuit. 
   According to another embodiment, an electronic controller for a high-power gas discharging lamp bulb includes a FU surge protector that is connected in series to a power input. A piezoelectric resistor connects to the FU surge protector. A plurality of transformers are in parallel with a plurality of capacitors, which electrically communicate with the piezoelectric resistor and the power input. A bridge rectifier in electrical parallel communication with the plurality of inductors and capacitors generates a DC power signal. The controller includes a power factor switching transformer, a first transistor, and a first integrated circuit receiving as an input an output of the power factor switching transformer. The first integrated circuit has an output control signal that is sent to the first transistor to control the voltage and current driving the first transistor. A power factor resistor and a power factor capacitor are electrically connected in parallel, with an input supplied by the first transistor. The power factor capacitor decreases the current ripple of the power signal, and the power factor resistor absorbs the discharging of the capacitor to balance the ripple tolerance of the capacitor, thereby creating a stabilized power signal having a corrected power factor value. 
   The embodiment may further include a potentiometer in series with a first power control resistor. A second power control resistor connects to the output of the power factor resistor and to the first power control resistor. A first power control capacitor connects between the potentiometer and the first power control resistor, and the second power control resistor. A second integrated circuit has as inputs a power signal from the potentiometer and a power signal from the second power control resistor, so that the second integrated circuit compares the two power signals. A second power control capacitor is at a first output of the second integrated circuit. A power control transformer electrically communicates with the second power control capacitor. A second transistor electrically communicates with the power control transformer. A third transistor electrically communicates with a second output of the second integrated circuit. 
   The embodiment may further include a blocking capacitor connecting outputs of the first and second transistors, carrying high frequency AC power to the lamp bulb. A third integrated circuit has an input that electrically communicates with the second and third transistors. An initiation trigger resistor electrically communicates with an output of the second transistor. A relay has a switch controlled by an output of the third integrated circuit and includes a first contact connectable to the initiation trigger resistor. An initiation trigger capacitor is connectable to a second contact of the relay switch, such that when the switch is closed, the initiation trigger capacitor is charged by the power passed through the initiation trigger resistor. An initiation trigger transformer connected between the initiation trigger capacitor and the lamp bulb is to discharge the initiation trigger capacitor, and thus produce a higher trigger voltage to the lamp bulb. 
   The embodiment may further include a SCR (silicon controlled rectifier) whose gate and T electrodes are connected to different input pins of the third integrated circuit to produce a pulse train in the output of the third integrated circuit, thus triggering the lamp bulb in succession. An accessory power supply circuit has as an input the DC power signal output of the bridge rectifier, wherein an output of the power supply circuit delivers a required voltage to the first, second, and third integrated circuits. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a block diagram of the controller disclosed herein. 
       FIGS. 2A and 2B  together are one electrical circuit diagram of the controller of  FIG. 1 , showing the circuitry details of each block displayed in  FIG. 1 . 
   

   DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
   The various embodiments of the present disclosure will be best understood by reference to the drawings, wherein like parts are designated by like numerals throughout. It will be readily understood that the components of the present disclosure, as generally described and illustrated in the figures herein, could be arranged and designed in a wide variety of different configurations. Thus, the following more detailed description of the embodiments of the apparatus, system, and method of the present disclosure is not intended to limit the scope of the disclosure, but is merely representative of its various embodiments. 
   The disclosed controller functions to control a high-power gas discharging lamp. The controller not only is light in weight and compact in volume, but also has simple circuitry, is low cost, has fewer components, and is easy to install. Furthermore, its drive waveform has low distortion and can work steadily and reliably with constant current, voltage, and power. It is particularly well-suited to be applied to a high-power gas discharging lamp. 
   Referring to  FIG. 1 , an electronic controller  100  for a high-power gas discharging lamp comprises, inter alia, a filter circuit  1 , a rectifying circuit  2 , a power factor switching circuit  3 , a driver inversion and power control circuit  4 , an initiation trigger protective circuit  5 , an output matching circuit  7 , and an accessory power supply circuit  6 , which may be sequentially connected, except for circuit  6 , which supplies power to circuitry of the controller  100 . 
   Referring to  FIGS. 2A and 2B , the power factor switching circuit  3  is formed by a thick film integration circuit IC 1 , which connects to a transistor switch Q 1  and transformer L 4 , respectively, such that the switch Q 1  is connected to a diode D 2  and to resistors R 4 , R 3 . The driver circuit of the power inversion control is formed by a thick film integration circuit IC 2 , which connects to a transistor switch Q 3 . The Q 3  switch connects to resistors R 8 , R 11 , and to a voltage regulator diode ZD 3 . A transistor switch Q 2  is connected to voltage regulator diodes ZD 1 , ZD 2 , resistors R 9 , R 10 , transformer T 2 , and capacitor C 8 . The initiation trigger protective circuit is formed by a thick film integration circuit IC 3 , which connects to capacitor C 10 , to a silicon controlled rectifier (SCR), to a diode D 4 , to capacitors C 9 , C 11 , to transformer L 5 , and to relay JT. 
   The disclosed controller transforms 50 Hz AC (alternating current) power supply into a 30 KHz higher frequency AC power supply so as to power up all electronic structures of the lamp and controller. The controller is compact, its weight is only about one-fourth that of conventional controllers, and has a high power factor, e.g., approximately 1. Adopting a multilevel common mode (differential mode filter), the filter circuit of the controller can lessen the electromagnetic, radiated, and conducted interference produced during activation of an on-off switch. Filtering circuitry also rejects interference to the controller, which is caused by input power supply noise. The controller meets the standard of EIECEE (Euro IEC Conformity for Testing and Certification of Electric Equipment). 
   The present disclosure is implemented with three integrated circuits (ICs), which result in high-integration, fewer required parts, simple circuitry, and low-cost design. The accessory power supply circuit, which supplies power for the ICs, works after electric power passes through the transformer and the voltage regulator tube, thereby making the controller highly stable and reliable. By having integrated circuit IC 2  drive transistor switch Q 3 , the driving circuit is simplified, has lower distortion, is able to work with constant current, constant voltage, and constant power. The driving circuit is thus capable of working steadily under short circuit, open circuit, and abnormal conditions. The controller also has a special start-up trigger circuit. Therefore, the controller is particularly well-suited to application with high-power gas discharging lamps in having a high power factor, long service life, high quality of lighting, and in meeting electromagnetic compatibility standards and environmental protection demands. 
   Referring again to  FIGS. 1 and 2A , block  1  is a filter circuit  1 . As soon as a lamp switch (not shown) is turned on, there will be a voltage surge delivered to the controller  100 . R 1 , a piezoresistor, absorbs the transient voltage surge and protects the controller  100  from a high transient voltage impulse. R 2 , an NTC (negative temperature coefficient) thermistor, is used to suppress the transient current surge of the power supply and achieves a soft startup. The input power supply causes noise and/or interference. A multilevel common mode, implemented through a differential mode filter, comprises capacitors C 1 , C 2 , C 3 , and C 4  and transformers L 1 , L 2 , and L 3  and works bilaterally, thereby lessening the electromagnetic, radiated, and conducted interference produced when turning the lamp switch on and off and rejecting the interference to the controller. 
   The filter circuit  1  is connected to the FU protector tube from the L side by phase conductors. The other side of the FU protector is connected to resistor R 1 , C 1 , and port  1  of L 1 . The ground reference conductor, N, is connected to R 1 , C 1  and to port  3  of L 1 . Port  2  of L 1  is connected to C 2  and to port  1  of L 2 . The other end of C 2  is connected to port  4  of L 1 . Port  2  of L 2  is connected to C 3  and to port  1  of L 3 . Port  4  of L 2  is connected to C 4  and to port  3  of L 3 . The other end of C 3  is connected to the other end of C 4 . 
   Block  2  is a rectifying circuit. D 1 , a bridge rectifier, is used to transform AC (alternating current) into DC (direct current), which supplies the controller after being filtered by capacitor C 6 . Rectifying circuit  2  connects to port  2  of L 3 , which is connected to one end of R 2  and to port  1  of transformer T 1 . The other end of R 2  is connected to port  1  of D 1 . Port  3  of D 1  is connected to the cathode of capacitor C 13 . Port  4  of D 1  is connected to pin  2  of IC 1  (discussed below). Port  4  of L 3  is connected port  2  of D 1 , and to port  2  of transformer T 2 . 
   Block  3  is a power factor switching circuit. IC 1  is a thick film integration circuit, such as an MC33262 power factor controller chip. The main function of IC 1  is to increase the power-factor and control the voltage and current of switch Q 1 . Q 1  (and other Q transistor switches discussed herein) are either a metal oxide-semiconductor field-effect transistor (MOSFET), or another transistor capable of operating in high voltage ranges, as herein discussed. 
   Sampled from the auxiliary winding of transformer L 4 , the current signal is sent to pin  5  of IC 1 . Sampled from the junction of D 2  and C 7 , the voltage signal is sent to pin  1  of IC 1 , and the feedback signal, sampled from resistor R 4 , is sent to pin  6  of IC 1 . The parallel connection switching power supply, made up of voltage boosting transformer L 4 , and field effect transistors (FETs) Q 1 , Q 2 , boosts the rectified 200V DC up to about 395V DC. After performing a smoothing filtration, capacitor C 7  further decreases the ripple current. The discharging resistor R 5  absorbs the charging and discharging peak current, balancing the tolerance of the electrolytic capacitor C 7 . 
   As displayed, the power factor switching circuit  3  comprises pin  1  of IC 1 , which is connected to the anode of diode D 2 , to R 5 , and to the anode of C 7 , and is also connected to the D electrode of Q 2 . Pin  2  of IC 1  is connected to C 6 , to port  4  of D 1 , and to port  1  of L 4 . Pin  4  of IC 1  is connected to the other end of R 3 . The S electrode of Q 1  is connected to one end of R 4 , and the other end of R 4  is connected to one end of R 5 . The cathode of C 7  is connected to one end of R 6 . Pin  7  of IC 1  is connected to resistor R 13 . Port  2  of L 4  is connected to the cathode of D 2  and to the D electrode of Q 1 . 
   Referring again to  FIGS. 1 and 2B , block  4  is a driver inversion and power control circuit. IC 2  is a thick film integration circuit, such as an LM358 chip containing low power dual operational amplifiers, for driver and power control. The signal obtained by potentiometer WR, resistor R 7 , and capacitor C 14  from the current sampling resistor R 6 , is sent to pins  1  and  3  of IC 2  for comparison within IC 2 . The comparison signal is sent into IC 2 , which controls the output signals at pins  4  and  5 . C 8  provides coupling capacity, and T 2  is a driving transformer. R 8  and R 9  are current limiting resistors. R 10  and R 11  are clamp resistors. Voltage regulation diodes ZD 1 , ZD 2 , and ZD 3  protect the gate electrode G of field effect transistors Q 2 , Q 3  when operating in both the forward and the reverse directions. Q 2  and Q 3  each comprise a half bridge switching circuit, which change the operational DC voltage to an AC voltage of about 30 Hz for supplying power to an intense discharge (ID) bulb  110  (in block  7 ). The “BC” port of potentiometer WR is connected to C 14  and R 7 , and by adjusting the WR potentiometer, the power may be adjusted from a few watts up to one thousand watts. 
   The driver inversion and power control circuit  4  comprises one end of R 7 , which is connected to the other ends of R 6 , R 4 , R 5 , to the cathode of capacitor C 7 , to pin  3  of IC 1 , to port  3  of L 4 , to the other end of C 6 , to the cathode of voltage regulator tube ZD 4 , to the cathodes of capacitors C 13  and C 18 , and to port  3  of bridge rectifier D 1 . Pin  3  of IC 2  is connected to the other end of C 14 , to the other end of R 6 , port  2  of T 2 , to the cathode of C 18 , to R 11 , to the cathode of ZD 3 , to the S electrode of Q 3 , and to one end of C 15 , which are all connected together. Pins  2  and  6  of IC 2  are connected to the anode of C 18 . Pin  4  of IC 2  is connected to C 8 . The other end of C 8  is connected to port  1  of T 2 . Pin  5  of IC 2  is connected to R 8 . The other end of R 8  is connected to R 11 , to the anode of ZD 3 , and to the gate G electrode of Q 3 . Port  3  of T 2  is connected to R 9 . The other end of R 9  is connected to one end of R 10 , to the anode of ZD 1 , and to the gate G electrode of Q 2 . Port  4  of T 2  is connected to the other end of R 10 , to the anode of ZD 2 , to the S electrode of Q 2 , to the D electrode of Q 3 , to C 15  and to C 12 . The cathode of ZD 1  is connected to the cathode of ZD 2 . The D electrode of Q 2  is connected to R 12  and to the anode of D 2 . 
   Block  5  is an initiation trigger protective circuit  5 . IC 3  is a start-up trigger thick film integrated circuit, such as SG3525 chip containing regulating pulse-width modulators. High frequency AC charges capacitor C 11  through resistor R 12  and then C 11  discharges. The discharge voltage from C 11  is coupled from the auxiliary winding to the main winding of transformer L 5 , which supplies start-up voltage for the bulb  110 . When the bulb is lighted, relay JT will cut off the working voltage automatically, at which time C 9 , C 11 , and a SCR (silicon controlled rectifier) will lose power, and the circuit steps into voltage stabilization. C 15  absorbs the voltage pulse spike, and the capacitance of C 10  is used to determine the RC time constant of the initiation trigger protective circuit  5 . 
   The initiation trigger protective circuit  5  comprises pin  1  of IC 3 , which is connected to the gate G electrode of the SCR. Pin  2  of IC 3  is connected to the T electrode of the SCR, to C 9 , to C 11 , and to the B electrode of relay JT. Pin  3  of IC 3  is connected to the gate G electrode of relay JT and to the anode of D 4 . Pin  4  of IC 3  is connected to the D electrode of relay JT and to the cathode of D 4 . Pin  4  is also connected to the S electrode of the SCR, to the cathode of C 10 , to the other end of R 6 , and to ports  2  and  4  of L 5 . Port  1  of L 5  is connected to the other end of C 11 . Pin  5  of IC 3  is connected to the anode of C 10 . Pin  6  of IC 3  is connected to the anode of C 18 . The A electrode of relay JT is connected to R 12 . The other end of R 12  is connected to the D electrode of Q 2  and to the anode of D 2 . 
   Referring again to  FIG. 2A , block  6  is an accessory power supply circuit  6 . Switching in from blocks  1  and  2 , transformed by T 1 , and rectified by D 3 , circuit  6  outputs an approximate 15V voltage from the filter circuit  1 . After the output is filtered by the RC circuit comprising R 13  and C 13 , and is stabilized by a voltage regulator diode ZD 4 , the output is then sent to each integrated circuit, thereby supplying current to integrated circuits IC 1 , IC 2 , and IC 3 . Transformer T 1  and rectifier D 3  may, of course, be adjusted to provide a different voltage (other than 15V), as required by IC 1 , IC 2 , and IC 3 . 
   The accessory power supply circuit  6  comprises port  1  of transformer T 1 , which is connected to port  2  of L 3 , and to R 2 . Port  2  of T 1  is connected to port  2  of D 1  and to port  4  of L 3 . Port  3  of T 1  is connected to port  2  of bridge rectifier D 3 . Port  4  of T 1  is connected to port  1  of D 3 . A common ground is formed by the common connections of: port  3  of D 3 , port  3  of D 1 , the cathodes of C 13  and C 18 , the cathode of voltage regulator diode ZD 4 , pin  3  of IC 1 , port  3  of L 4 , one end of R 4 , C 7 , R 6 , and R 7 . Port  4  of D 3  is connected to R 13 . The other end of R 13  is connected to the anode of C 13 , to the anode of ZD 4 , to pin  7  of IC 1 , to pins  2  and  6  of IC 2 , to pin  6  of IC 3 , which are connected together to form a low voltage operational power supply channel. 
   Block  7  is an output matching circuit  7 , to match the impedance of the lamp bulb, thus to maximize output power to the bulb. Block  7  comprises capacitor C 12 , the intense discharge (ID) lamp bulb  110 , and the auxiliary winding of transformer L 15 . The ID bulb  110  can be a cold cathode luminous tube in addition to many types of dysprosium, indium selenide, natrium, or metal halide bulbs, to name a few. 
   The output matching circuit  7  comprises C 12 , which is connected to C 15 , to the S electrode of Q 2 , and to the D electrode of Q 3 . The other output end of C 12  is connected to the ID bulb  110 . Port  4  of L 5  is connected to port  2  of L 5 , to C 9 , and to the S electrode of the SCR. Port  3 , or the output port, of L 5  is connected to the other end of the ID bulb  110 . 
   Referring again to  FIG. 2A , after the lamp is switched on, block  1  provides 50 Hz AC to the filter circuitry of block  1 , and R 1  absorbs the transient surge voltage from the power supply. To discern amongst the three levels of common mode, the differential mode combination filter comprises transformers L 1 -L 3  and capacitors C 1 -C 4 , which reject (or filter) the interference from the input power supply and from the controller  100  bilaterally so as to make the controller  100  electromagnetically compatible with international standards of the USA, Europe, and other countries. 
   After being filtered, the power signal is divided into two signals: one accesses block  6 , and the other accesses block  2 , and then is rectified into about 200V DC. Block  3  functions to realize voltage stabilization, current stabilization, and power factor correction by controlling the Q 1  switch. 
   The input DC voltage signal of the controller  100  from block  6  is sent to pin  2  of IC 2  and the output DC signal is sent to pin  1  of IC 1 . When the voltage of the input power supply is changed, the input and the output voltage signals will be compared in IC 1 . The benchmark in IC 1  will react, and pin  4  of IC 1  will output the resultant voltage signal, which in turn controls the Q 1  switch so as to achieve voltage stabilization. The DC inputs from port  1  of L 4  and outputs from port  2  of L 4 . Transformed to ports  3  and  4  of L 4 , the current signal is processed and analyzed in IC 1 . Then, pin  4  of IC 1  outputs a control signal so as to achieve current stabilization. 
   Through L 4 , Q 1 , and D 2 , the operating voltage is increased, the phase of the voltage is increased, the voltage phase is in the wake of the current phase, and the power factor is increased to nearly 1. The stable output of power supply is sent to block  4 . 
   Again referring to  FIG. 2B , block  4  functions to realize voltage driver inversion and power control. IC 2  outputs the high frequency oscillation signal from pin  4 . Coupled by C 8 , isolated and matched by T 2 , the output signal drives Q 2 . Pin  5  directly couples to Q 3  with current limiting through R 8 , which drives Q 3 . Working, in turn, in the upper half period and in the lower half period, Q 3  transforms the stable DC voltage into high frequency AC voltage, and the inversion frequency is set in IC 2 . 
   When power loading or the power of the bulb is changed, the current of the controller  100  is changed accordingly. R 6  is the current sampling resistor of the controller  100 . The sampling signal is sent through R 7  from one end of R 6 . The signal on the other end of R 6  is sent to pin  3  of IC 3 . A part of the signal, passing through the connection point of R 7  and C 14 , is sent to potentiometer WR. Adjusted by WR, the signal is sent to pin  1  of IC 3 . After processed in IC 3 , the signal is delivered from pin  4  of IC 2  to control the output value of Q 2  and Q 3 . Thusly, the loading ability of the controller  100  is changed according to the change of the loading, e.g., the impedance of the ID lamp bulb  110 . 
   Block  5  is the initiation trigger protective circuit. The high frequency AC power supply is sent to the ID bulb  110  by Q 2  and Q 3  through block  7  and blocking capacitor C 12 . The high DC voltage, controlled by R 12 , charges C 11  through relay JT, which is normally closed. After C 11  is charged, C 11  discharges through L 5 . At this time, the winding between pins  1  and  2  of L 5  produces induced electromotive force, which induces the winding between pins  3  and  4  of L 5  to produce higher trigger voltage, thus lighting the ID bulb  110  of the tube. When the tube is lighted, the C and D ports of relay JT receives the electricity, wherein JT is attracted and the initiation trigger protective circuit is closed. 
   If the ID bulb  110  is changed or the load fails, relay JT is still closed and C 11  does not get the trigger voltage, so there is no discharging process and L 5  has no induced voltage. In the case of the latter, the lamp cannot be lighted, and the controller  100  is protected. Because of the variance of power and varying features present in different kinds of tubes, there is a set of oscillation switching signals in IC 3 . The SCR produces a pulse train of these signals through pins  1  and  2  of IC 3 , and the pulse train triggers the ID bulb  110  in succession. If there exists lamp holder creepage, cap corruption, glass shell cracking, or other failure, C 9  will feedback the signal to IC 3 , which will stop outputting pulse train, thereby protecting the controller  100 . After the failure is removed, IC 3  will start up again. 
   The input operating voltage ranges from 150V to 250V; the operating frequency ranges from 50 Hz to 60 Hz; and the operating power ranges from 150 W to 2000 W. 
   It will be obvious to those having skill in the art that many changes may be made to the details of the above-described embodiments without departing from the underlying principles of the invention. The scope of the present invention should, therefore, be determined only by the following claims.