Electric lamp and discharge devices: systems – Periodic switch in the supply circuit – Impedance or current regulator in the supply circuit
Reexamination Certificate
2000-09-13
2002-02-26
Vu, David (Department: 2821)
Electric lamp and discharge devices: systems
Periodic switch in the supply circuit
Impedance or current regulator in the supply circuit
C315S307000, C315S247000, C315SDIG007, C315S119000
Reexamination Certificate
active
06351081
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an electronic ballast for a high intensity discharge lamp.
BACKGROUND OF THE INVENTION
Generally, there have been presented various types of arc tube lamps such as, for example, a fluorescent lamp commonly used in general houses, a lighting lamp used in factories, a street lamp installed on the street and so on. In this case, the fluorescent lamp, an ultraviolet rays lamp and a low pressure sodium vapor lamp are contained within low pressure discharge lamps, and the street lamp is included within high pressure discharge lamps. Referring to features of the low pressure discharge lamp, it has a long length of tube, so that the heat generated within the tube is discharged to the outside to thereby allow tube atmosphere to be same before or after the lamp is lighted. Therefore, the low pressure discharge lamp has a constant tube voltage at the time when the lighting of the lamp is initialized and after it is completed, so that it can easily adapt an electronic ballast without any problem. On the other hand, examples of the high pressure discharge lamp are a mercury lamp, a high pressure sodium vapor lamp, a metal halide lamp and the like, which are generally called a high intensity discharge(HID) lamp. Referring now to the features of the high intensity discharge lamp, it has a relative short length of tube but a high power. If the high intensity discharge lamp is lighted, the interior of the tube becomes at a substantially high temperature of plasma state, which causes air atmosphere within the tube to be tremendously high when compared with the time before the lamp is lighted. In the case where a constant amount of tube current is applied, the tube voltage upon the lighting of the lamp is much different from that after the lighting of the lamp is completed. In addition, even when the lamp is stabilized and operated, under the effect of a negative resistance impedance in the lamp, an impedance is high over the tube voltage and contrarily, it is low below the tube voltage. To light such the high intensity discharge lamp, a prior art leakage transformer type ballast has been generally employed. The leakage transformer functions as a current source and has a function of limiting an amount of the current regardless of the impedance of lamp. As a result, when the lamp is initially lighted the tube voltage approaches a potential of zero voltage, and when the lighting of lamp is stabilized, it is changed to a normal potential. To high the inductance of the leakage transformer, however, a long coil for winding the transformer is required, which renders the efficiency of the leakage transformer really deteriorated.
To solve the disadvantage of the leakage transformer, an electronic ballast using an electronic control method is newly employed. Owing to the introduction of the electronic control method, there are generated several advantages in that the efficiency thereof is high, the volume thereof is small, the weight thereof is light, and an added external control is easily executed.
A direct current(DC) power source applied to the conventional electronic ballast should be a regulated voltage source and, if a ripple voltage exists in the regulated voltage source, the light of lamp is flickered or is automatically turned off due to the negative resistance impedance characteristic of the lamp. Furthermore, the power source outputted to the lamp should be a current source. To this end, the regulated DC power source should be inverted into the lamp power. Therefore, the electronic ballast circuit is preferably comprised of a converter part and an inverter part. Various kinds of control methods in the converter part and the inverter part are suggested, and hereinafter, an explanation of the advantages and disadvantages thereon will be in detail discussed.
Converter Part
1) condenser input type control method: An alternating current(AC) line power of about 50 Hz or 60 Hz is full wave rectified, and to suppress a ripple factor in the full wave rectified power, a large capacity of condenser is installed. In the control method, however, an input power factor falls to a percentage of about 55%. Moreover, upon application of the initial power, an inrush current greatly flows. Accordingly, the control method is not adapted for a large capacity of electronic device, because of the above-mentioned problems.
2) choke input type control method: To solve the problem occurring in the condenser input type control method, a choke coil is inserted into the front end of the condenser. A ripple rate is variable in accordance with the current value, and to decrease the ripple rate, a large capacity of choke coil is necessary. However, the choke input type control method is not well adapted because the choke coil for improving the power factor should be designed in a large size.
3) chopper regulator type control method: This method is used to decrease the capacity of the choke coil by using a switching transistor. The method is classified into a step-down converter method and a step-up converter method. In the step-down converter method, a control voltage is lower than an input power, and contrarily, in the step-up converter method, the control voltage is higher than the input power. Accordingly, the method can arbitrarily adjust the control voltage by using both the step-down converter and the step-up converter. In the method, however, there occur the problems in that the power loss can not be avoided because of the installation of the switching transistor and noises are greatly generated due to a reverse recovery current of a flywheel diode, which is combined with the switching transistor.
Inverter Part
1)DC current source control method: In the high intensity discharge lamp, a mercury lamp contains mercury within the tube thereof, and does not form any material therein. A high pressure sodium vapor lamp or a metal halide lamp spreads a lighting color material over the electrode thereof or pastes a part of the tube with the material. If a DC current source is applied to the lamp, the two poles of the lamp have different temperatures from each other. In this case, there occurs no problem in lighting the mercury lamp, but there occurs the problem in that the sodium vapor lamp or the metal halide lamp can not emit a desired lighting color. As a result, for the application of the lamp power source, the regulated DC voltage source should be inverted into the alternating current source. Therefore, this method can be adapted only for the embodiment of the mercury lamp.
2) low frequency inverter type control method in a full bridge manner: A full bridge switching transistor inverts a frequency into a low frequency and controls an output in a chopper regulator type. And, the full bridge switching transistor generates a current source in the step-down circuit on the chopper regulator. If the full bridge switching transistor does not operate as the current source, theoretically the output current infinitely flows due to the negative resistance impedance characteristic of the lamp. The above method has the advantages of a good input power factor and a stabilized power control, but has the disadvantages of a low efficiency of about 84%, lots of noises and a large number of parts.
3) a high frequency inverter type control method: If the power of inverter part is the regulated DC power source, the method employs a series resonant inverter to thereby connect a series resonant condenser in parallel with the lamp. In the series resonant circuit, lighting of the lamp can be easily implemented since a series resonant inductance is operated as a current source. The power control of lamp is executed with a higher frequency than a resonant frequency. In a frequency adjustable control, the current or power of lamp is detected to thereby control the frequency of switching transistor. The above method has the advantage of a simple output circuit. On the other hand, there occurs a defect in that since the DC power source should be the regulated power source, the AC line power has
Alemu Ephrem
Notaro & Michalos P.C.
Vu David
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