Electric lamp and discharge devices: systems – Periodic switch in the supply circuit – Silicon controlled rectifier ignition
Reexamination Certificate
2000-02-22
2001-06-12
Wong, Don (Department: 2821)
Electric lamp and discharge devices: systems
Periodic switch in the supply circuit
Silicon controlled rectifier ignition
C315S224000, C315S307000
Reexamination Certificate
active
06246181
ABSTRACT:
TECHNICAL BACKGROUND OF THE INVENTION
This invention relates to a discharge lamp lighting device which rectifies and smoothes AC power into DC power, and supplies a high frequency power to a load circuit including a discharge lamp by converting the DC power thus obtained through the rectification and smoothing into a high frequency voltage.
DESCRIPTION OF RELATED ART
A known example of the discharge lamp lighting device of the kind referred to has been disclosed in U.S. patent application Ser. No. 09/042,555, in which a circuit is formed to include a rectifier for full-wave rectification of AC source power, and to connect a capacitor of a relatively small capacity across output terminals of the rectifier. Further, a smoothing capacitor and a series circuit of a pair of first and second transistors connected in parallel with the smoothing capacitor are provided, while a low potential side terminal of the smoothing capacitor is connected to a low potential side DC output terminal of the rectifier. Across a high potential side DC output terminal of the rectifier and a junction point the pair of transistors, a primary winding of a transformer is connected. A load circuit is connected to a secondary winding of the transformer, which load circuit comprises such discharge lamp as a fluorescent lamp having filaments connected at respective one end across the secondary winding of the transformer, and a preheating and resonating capacitor connected across the other non-discharge lamp lighting device side ends of the filaments of the lamp, so that a resonance circuit is constituted by a leakage inductance of the transformer and the preheating, resonating capacitor. Further, the pair of transistors comprise bipolar transistors, and a diode is connected in inverse parallel to each of these transistors, which transistors are provided to be alternately turned ON and OFF by means a control circuit (not shown) at a sufficiently higher frequency than a power source frequency.
Referring to the operation in stationary state of this known device, the smoothing capacitor is charged in the stationary state, so that, as the first transistor turns ON, there flows a current through a path including the smoothing capacitor, the first transistor, the primary winding of the transformer, the capacitor connected across the output terminals of the rectifier and the smoothing capacitor, and a power is supplied through the transformer to the load circuit, upon which a voltage across the smoothing capacitor is caused to increase due to its resonance. As the first transistor turns OFF, an energy accumulated in the primary winding of the transformer is discharged, the current continues to flow through a path including the transformer, the capacitor connected across the output terminals of the rectifier, the diode and the transformer, and the voltage across the capacitor connected across the output terminals of the rectifier further increases.
As the second transistor turns ON next, a resonance action of the leakage inductance of the transformer with the preheating and resonating capacitor and the capacitor connected across the output terminals of the rectifier causes a resonance current to flow through a path including the capacitor across the output terminals of the rectifier, the transformer, the second transistor and the capacitor across the output terminals of the rectifier, upon which the voltage across the capacitor connected across the rectifier starts decreasing. As this voltage becomes lower than the DC output voltage of the rectifier, an input current from the AC power source is drawn in, and the current flows through a path including the AC power source, the rectifier, the transformer, the second transistor, the rectifier and the AC power source. As the second transistor turns OFF, the current continues to flow through a path including the AC power source, the rectifier, the transformer, one of the diodes, the smoothing capacitor, the rectifier and the AC power source, and the initial state restores as the first transistor turns ON.
Now, in the circuit of this kind for providing the high frequency power to the load circuit, it has been generally taken a measure of inserting a high-frequency blocking filter circuit between the AC power source and the rectifier, in order to prevent any high frequency component from being mixed into the AC source power. With the use of such filter circuit, the input current from the AC power source is made substantially proportional to the AC source power voltage.
As to an input current waveform, the capacity of the capacitor connected across the output terminals of the rectifier will be an important factor. When the voltage across the smoothing capacitor becomes large in the amplitude, for example, the polarity is inverted in a period in which the input current flows from the AC power source to the high frequency blocking filter, and a remarkable noise occurs. Further, when the voltage across the smoothing capacitor becomes small in the amplitude, there occurs a quiescent period in the input current to the high frequency blocking filter. In either event, the noise is caused to be mixed with the AC source power, and the capacity of the capacitor connected across the output terminals of the rectifier is properly set, whereby not only the higher harmonics of the input current can be reduced but also the input power factor can be elevated.
In another example shown in Japanese Patent Laid-Open Publication No. 10-14257, there has been suggested a discharge lamp lighting device in which a second impedance element is connected between a junction point of an output terminal of the rectifier with a diode and a series circuit of a coupling capacitor and an inductor, and a load circuit is connected through a diode across the second impedance.
In this known device, however, the load current becomes high in troughs and low at crests of pulsating current. In order to lower the crest factor of the load current, in this case, it is required to increase the voltage of the smoothing capacitor, and required costs for manufacturing the device are increased by required measure for increasing the withstand voltage of the smoothing capacitor. Upon turning ON of the other transistor, the resonating current is caused to be superposed on the input current, so that a current flowing through the transistor at the moment when the other transistor turns OFF will be large, so as to be remarkably larger particularly at the pulsation crests where the input current reaches its peak. For this reason, there arises a problem that the switching loss at the other transistor is increased due to increments in the voltage and switching current of the smoothing capacitor, so as to lower the circuit efficiency.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a discharge lamp lighting device which generates less higher harmonics in the input current, renders the crest factor of the current flowing to the load circuit to be small even when the voltage of the smoothing capacitor is low, and reduces the loss at the switching elements.
According to the present invention, the above object can be accomplished by means of a discharge lamp lighting device comprising a rectifier for rectifying an AC power into a DC power, first diode connected at one end in forward direction to one of output terminals of the rectifier, a smoothing capacitor connected between the other end of the diode and the other output terminal of the rectifier, second diode connected at one end in forward direction to the other end of the first diode, first and second capacitors connected respectively in parallel to the first and second diodes, a pair of switching elements connected in series between the other end of the second diode and the other output terminal of the rectifier, third and fourth diodes connected respectively in inverse parallel to each of the pair of the switching elements, a load circuit including a discharge lamp, and an inductor element connected between a junction point of the pair of the switching elemen
Hori Kazuhiro
Kanda Takashi
Naruo Masahiro
Ohnishi Masahito
Burns Doane , Swecker, Mathis LLP
Lee Wilson
Matsushita Electric & Works Ltd.
Wong Don
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