Electric lamp and discharge devices: systems – Periodic switch in the supply circuit – Impedance or current regulator in the supply circuit
Utility Patent
1999-12-06
2001-01-02
Vu, David (Department: 2821)
Electric lamp and discharge devices: systems
Periodic switch in the supply circuit
Impedance or current regulator in the supply circuit
C315S291000, C315SDIG001, C363S034000
Utility Patent
active
06169374
ABSTRACT:
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. A particularly effective type of electronic ballast, or converter, has a load circuit using a resonance inductor or transformer having a linear core, generally together with MOSFET switches (metal oxide silicon 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 resonance inductor in a series connected load circuit between the inverter output and signal ground. The inductor has secondary windings connected to the control terminals of the switching transistors. The load circuit includes a tuning capacitor C8 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.
BRIEF SUMMARY OF THE INVENTION
An object of the invention is to provide a high frequency electronic converter with superior power factor correction and low cost.
Another object of the invention is to provide electronic lamp ballasts with superior power factor correction and low cost.
A further object of the invention is to reduce current stress in the resonant load circuit of an electronic ballast used to power a fluorescent lamp.
Yet another object of the invention is to provide an electronic ballast which operates efficiently and effectively with a constant inverter frequency.
According to the invention, a high frequency converter circuit including a half-bridge inverter circuit has a voltage source feedback path, including a capacitor, to one terminal at the AC side of the line voltage rectifier circuit, and a current source feedback path to the other terminal at the AC side of the line voltage rectifier circuit. The converter includes two source connection points between which the low frequency line voltage is maintained, and a series inductor between one of these connection points and the rectifier input. The series inductor has an impedance which is not large enough to function as a high frequency blocking inductor; rather, the series inductor carries a substantial high frequency current.
Preferably, the current source feedback is obtained by connecting a resonant load circuit, including a resonance inductor in series with load connection terminals, between the output node of the inverter and the other terminal at the AC side of the line voltage rectifier circuit, with one of the load connection terminals being connected to the AC-side terminal, while the voltage feedback is from the other load connection terminal.
In one preferred embodiment, the converter includes a further high frequency capacitor connected between a first of the AC-side terminals of the line voltage rectifier circuit and one of the DC side terminals. In this embodiment, the load may be a fluorescent lamp, connected directly in series with the resonance inductor or through a matching transformer.
In another preferred embodiment, the load is a fluorescent lamp in parallel with a resonance capacitor. Alternatively, the primary winding of a matching transformer may be in series with the resonance inductor, at least one fluorescent lamp is connected across the secondary of the matching transformer, and the load circuit includes a resonance capacitor.
In yet another preferred embodiment, a small capacitance is connected between the two ac-side terminals of the rectifier. During part of a high frequency cycle this capacitor plays a role in determining the resonant frequency of the resonant load circuit. The resonance capacitor across the lamp is then not needed.
Prior art converters used as fluorescent lamp ballasts have required frequency modulation of the inverter frequency to achieve acceptable lamp crest factor (that is, less than 1.7), line power factor and total harmonic distortion. An important advantage of the invention is that, because both current and voltage feedback are provided, the converter can be operated at a constant switching frequency while still maintaining a low crest factor for the lamp current. At the same time the input line power factor and total harmonic distortion can be held within acceptable limits. Constant switching frequency not only simplifies the inverter control circuitry, but has the further advantage that an EMI filter, required by regulations in most U.S. jurisdictions, can be optimized for that frequency so as to use smaller components.
REFERENCES:
patent: 5223767 (1993-06-01), Kulka
patent: 5313142 (1994-05-01), Wong
patent: 5387848 (1995-02-01), Wong
patent: 5400241 (1995-03-01), Bergervoet
patent: 5459651 (1995-10-01), Maehara
patent: 5596247 (1997-01-01), Martich
patent: 5608295 (1997-03-01), Moisin
patent: 5686779 (1997-11-01), Moisin et al.
patent: 5764496 (1998-06-01), Sato et al.
patent: 5771159 (1998-06-01), Sako et al.
patent: 5798617 (1998-08-01), Moisin
patent: 4137207A1 (1993-05-01), None
patent: 0697803A2 (1996-02-01), None
PHA 23,611, U.S. Serial No. 09/222,904, Filed: Dec. 30, 1998.
PHA 23,618, U.S. Serial No. 09/245,757, Filed: Feb. 8, 1999.
Philips Electronics North America Corporation
Treacy David R.
Vu David
LandOfFree
Electronic ballasts with current and voltage feedback paths does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Electronic ballasts with current and voltage feedback paths, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Electronic ballasts with current and voltage feedback paths will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2435844