Electric lamp and discharge devices: systems – Periodic switch in the supply circuit – Impedance or current regulator in the supply circuit
Reexamination Certificate
1999-02-08
2001-02-06
Wong, Don (Department: 2821)
Electric lamp and discharge devices: systems
Periodic switch in the supply circuit
Impedance or current regulator in the supply circuit
C315S307000, C315S291000, C315SDIG007
Reexamination Certificate
active
06184630
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
SELF-OSCILLATING RESONANT CONVERTER WITH PASSIVE FILTER REGULATOR, Ser. No. 09/221,954, filed by C. Chang and assigned to the assignee of the instant application.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not Applicable
BACKGROUND OF THE INVENTION
The invention relates to electronic ballasts for operating discharge lamps such as fluorescent lamps, and in particular to such ballasts having a minimum number of active components.
Most magnetically coupled self-oscillating inverters are manufactured in large quantities for sale in a highly competitive market. Half-bridge inverters are widely used because they have a relatively low parts count. Such inverters may be classified into two groups: those using a current transformer having a saturable core, generally together with power BJT's (bipolar junction transistors); and those using a current transformer having a linear core, generally together with MOSFETs (metal oxide semiconductor field effect transistors). As those of ordinary skill will recognize, in this context a linear core is one in which operation is over a region having a curved B-H characteristic, rather than a sharp B-H characteristic; that is, at all times the flux level is such that a significant increase in magnetizing current will be accompanied by a significant increase in flux level.
U.S. Pat. No. 5,608,295 discloses such a ballast circuit having a linear core resonance inductor in a series connected load circuit between the inverter output and signal ground. The inductor has secondary windings connected to the control electrodes of the switching transistors. The load circuit includes a tuning capacitor C
8
and the primary winding of a matching transformer. Fluorescent lamps are connected to a secondary winding or windings of the matching transformer, and one or two additional tuning capacitors are connected across the lamps. A feedback conductor is connected between a tap on the primary winding of the matching transformer and a node between two 47 nf feedback capacitors which are connected in series across the AC input to a full wave bridge rectifier circuit. This patent teaches that the low frequency (power line) input current modulates in amplitude the high frequency feedback current which works as a carrier in order to transfer the low frequency input current through the bridge rectifier over most of the low frequency cycle. Accordingly it is clear that the line current is still discontinuous.
BRIEF SUMMARY OF THE INVENTION
An object of the invention is to provide a cost-effective solution to power factor correction in electronic ballasts.
According to the invention, in a low frequency to high frequency power converter including:
a capacitive source impedance source of low frequency line voltage, having source connection points between which the low frequency line voltage is maintained,
a DC supply circuit having at least two diodes and four terminals, and an energy storage capacitor, two of these terminals being AC-side terminals connected to the source connection points, and two of these terminals being DC-side terminals, one of the diodes being connected between one of the AC-side terminals and one of the DC-side terminals,
a half-bridge inverter connected to receive DC voltage from the DC-side terminals, the inverter comprising two switching transistors connected in series and having an output node between the transistors for providing a high frequency output voltage, and
a load circuit carrying a first high frequency current, connected between the output node and one of the DC-side terminals, the load circuit comprising a plurality of load circuit elements including a resonance inductor, at least one resonance capacitor forming part of a resonant circuit with the resonance inductor, and two load connection points for a non-linear load which is at least substantially resistive in an operating condition,
a high frequency capacitor provides a path for a second high frequency current, the high frequency capacitor being connected between one of the AC-side terminals and a location along the load circuit at which there is a voltage at the high frequency, the high frequency capacitor having a value selected such that the high frequency capacitor receives energy from one of said AC-side terminals during a first portion of every cycle of the high frequency voltage, and the high frequency capacitor transfers energy to the energy storage capacitor during a different portion of every cycle of the high frequency voltage.
In a first preferred embodiment, the non-linear load is a discharge lamp. One of the connections for powering the lamp, directly or through a matching transformer, is at signal ground, and the voltage feedback capacitor is connected to the other connection. In this embodiment during normal operation the DC supply circuit never transfers energy directly from the AC-side terminals to the energy storage capacitor.
In another embodiment, the feedback capacitor is connected directly to the inverter output. Preferably, there are two feedback capacitors from that point, one to each side of the AC line between an EMI filter and the rectifier input. In this embodiment, during intervals between conduction by one switching transistor and the other, the capacitors provide current feedback to the AC-side, and one of the capacitors is discharged before the next turn on of a switching transistor. Further, during a portion of each high frequency cycle of normal operation the line input provides energy directly to the load circuit.
Preferably, the DC supply circuit is a full wave bridge rectifier, having a respective fast recovery diode in series with each of the bridge DC connections.
REFERENCES:
patent: 4234822 (1980-11-01), Garrison et al.
patent: 5223767 (1993-06-01), Kulka
patent: 5387848 (1995-02-01), Wong
patent: 5608295 (1997-03-01), Moisin
patent: 5828185 (1998-10-01), Fellows et al.
patent: 5898278 (1999-04-01), Muessli
Bruning Gert W.
Qian Jinrong
Philips Electronics North America Corporation
Vo Tuyet T.
Wong Don
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