Electric lamp and discharge devices: systems – Condenser in the supply circuit – Inductance in the condenser circuit
Reexamination Certificate
2000-01-21
2002-08-06
Philogene, Haissa (Department: 2821)
Electric lamp and discharge devices: systems
Condenser in the supply circuit
Inductance in the condenser circuit
C315S224000, C315S247000, C315S2090SC, C315SDIG007
Reexamination Certificate
active
06429604
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to power feedback circuits. More particularly, the invention relates to a double path type power feedback circuit for multiple lamp parallel operation.
2. Description of the Background of the Invention
The low power factor (PF) of conventional electromagnetic compact fluorescent lamps (CFLS) is due to the fact that their voltage and current are not in phase and/or to the higher harmonic content in the current waveform. Electronics in the electronic CFLs, as well as in all other electronic equipment, generate harmonic currents. Harmonic currents are closely related to a reduced PF and can disturb other equipment. Furthermore, a very high harmonic distortion on a utility network may reduce the performance of the transformers and could ultimately damage them.
An electronic CFL has a typical power factor of between 0.5 and 0.6, but the current cannot be simply compensated for with a capacitor. Instead, a filter has to be introduced, either in the ballast of the lamp itself or somewhere in the electricity network. In countries where the International Electroctechnical Commission (IEC) standards are adopted, the lighting equipment must have a power factor better than 0.96 and a Total Harmonic Distortion (THD) below 33%. However an exception is made in the IEC lighting standards for equipment with a rated power of less than 25W.
The single stage electronic ballast based on the power feedback principles has been disclosed and described in numerous patents, including U.S. Pat. No. 5,404,082 in the names of A. F. Hernandez and G. W. Bruning, and entitled “High Frequency Inverter with Power-line-controlled Frequency Modulation,” and U.S. Pat. No. 5,410,221 in the names of C. B. Mattas and J. R Bergervoet, and entitled “Lamp Ballast with Frequency Modulated Lamp Frequency”. The type of ballast described in these patents has a lower parts count due to a modulation scheme imbedded in a power conversion process. These patents describe the conversion of a low frequency alternating current (AC) voltage source to a high frequency AC voltage source via a properly designed power feedback scheme. These patents further describe how the harmonic content of an input current can be limited within the International Electrotechnical Commission (IEC) specification while the output current crest factor remains acceptable. Topologically, the single stage power factor correction is achieved based on the power feedback to the node between the full-bridge rectifier output and the DC electrolytic capacitor.
To date, all of the power feedback schemes are used for a single lamp and a two lamp series configuration, with and without dimming. It is important to point out that in such a class of applications the value of the resonant converter parameters L and C are fixed, even though the load current can be changed during the dimming process. Technically, this implies that the circuit resonant frequency is fixed while the quality factor (Q) is changed with the load. The quality factor Q may be described as the ratio of the resonant frequency to bandwidth.
In the multiple lamp operation circuit
10
, shown in
FIG. 1
, lamps R
lp
are connected in parallel, via ballast capacitors C
1p
, respectively, due to the. independent lamp operation (ILO) requirements. Lamps R
lp
and ballast capacitors C
lp
are then connected in parallel to a transformer T
1
, which in turn is connected in parallel to a capacitor C
3
. Capacitor C
3
is connected to diodes D
3
, D
4
of the full-bridge rectifier represented by diodes D
1
-D
4
, and diodes D
1
, D
2
are connected to a resonant inductor L
1
, which in turn is connected to a diode D
5
. Diode D
5
is further connected to a drain terminal of a positive-negative-positive (PNP) transistor Q
2
, and the source terminal of transistor Q
2
is connected to a drain of a PNP transistor Q
3
. Gates of both transistors Q
1
and Q
2g
are connected to a high voltage control integrated circuit
12
.
A first terminal of a resistor R, is connected to the source terminal of the transistor Q
3
and a second terminal of this resistor is connected to a first terminal of the capacitor C
3
, a resistor R
2
and diodes D
3
and D
4
. The high voltage control integrated circuit
12
further connects to the connection of the source terminal of the transistor Q
3
and a first terminal of the resistor R
l
, individually to a capacitor C
2
, and to the interconnection of the inductor L
2
and capacitor C
3
. The capacitor C
2
and the inductor L
2
are serially interconnected. The inductor L
2
is further connected to the capacitor C
3
.
A capacitor C
1
is on a first side connected between a diode D
5
and the drain terminal of transistor Q
2
, and on the second side between diodes D
3
, D
4
and the resistor R
1
. A drain terminal of the PNP transistor Q
1
is connected to the junction of the inductor L
1
and the diode D
5
and the source terminal of the transistor Q
1
is connected to a resistor R
2
, which is also connected diodes D
3
and D
4
, and the capacitor C
1
. A power factor controller unit
14
is connected to the inductor L
1
, the gate of the transistor Q
1
, to the connection of the source terminal of transistor Q
1
and resistor R
2
, and to the connection of diode D
5
and capacitor C
1
.
In this configuration the resonant capacitance is strongly load dependent. This dependence with respect to 0 to 4 lamp combinations is shown in
FIG. 2
a
, where five distinct resonant frequency curves are charted on a voltage/frequency chart. Here, the zero lamp curve
20
represents a scenario in which no lamps are connected, the one lamp curve
22
represents a scenario in which one lamp is connected, the two lamp curve
24
represents a scenario in which two lamps are connected, the three lamp curve
26
represents a scenario in which three lamps are connected, and finally the four lamp curve
28
represents a scenario in which four lamps are connected. The respective frequency peaks of the curves
22
,
24
,
26
and
28
are 9.554215×10
4
, 7.52929×10
4
, 6.503028×10
4
, and 5.843909×10
4
.
FIG. 2
b
shows the same five distinct resonant frequency curves, charted on a primary side resonant tank input phase/frequency chart. In this graph, the zero lamp curve
30
reaches a low phase point of −90, the one lamp curve
32
reaches a low phase point of −23.360583, the two lamp curve
34
reaches a low phase point of −14.71952, and the three lamp curve
36
reaches a low phase point of −5.566823.
Traditionally, the power feedback power factor correction circuits are limited to a fixed load operation. When the load changes, the input line power factor and current THD performance drop. Even more severe situation is that the DC bus voltage increases dramatically as the load decreases. Such DC bus as voltage over boost usually leads to the damage of power switches if they are not substantially over designed. This problem is encountered during the development of a power feedback circuit for four lamp ballast circuits.
In view of those variables and the sinusoidal input voltage, it would be advantageous to have a simple single stage electronic ballast circuit based on the power feedback scheme for multiple lamp operation.
SUMMARY OF THE INVENTION
The ballast circuit of the invention is designed for a single or multiple lamp parallel operation, where at each lamp a condition may be controlled such that the amplitude (e.g. the switching frequency of the power transistors) output voltage is almost constant in the steady state. The present invention uses fewer high ripple current rated capacitors than the prior art while providing galvanic isolation. Furthermore, in addition to using smaller input filter sizes, the inventive circuit uses fewer fast reverse recovery diodes necessary for the prior art circuit schemes.
In order for the inventive power feedback circuit to work with multiple lamp combinations under variable load conditions and without severe DC bus voltage over boost, the r
Koninklijke Philips Electronics , N.V.
Philogene Haissa
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