Electric lamp and discharge devices: systems – Periodic switch in the supply circuit – Silicon controlled rectifier ignition
Reexamination Certificate
1998-12-21
2001-08-28
Vu, David (Department: 2821)
Electric lamp and discharge devices: systems
Periodic switch in the supply circuit
Silicon controlled rectifier ignition
C315S224000, C315S307000
Reexamination Certificate
active
06281636
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an inverter that rectifies and smooths alternating voltage, to convert it to a direct-current voltage, and then convert it to a high-frequency voltage, to supply high-frequency power across load. More particularly, the invention relates to a neutral point inverter, or a neutral point inverter type ballast suitable for lighting equipment.
BACKGROUND ART
In recent small-sized domestic products and office automation (OA) equipment, high-frequency inverters have been mounted for achieving high performance and high efficiency.
Also, in fluorescent lamp appliances for homes and fluorescent lamp appliances for facilities, a copper-iron type ballast, such as a choke current-limiting type, a leakage transformer type or the like, has hitherto been used as a circuit system that drives a fluorescent lamp. However, since it has limitations on the aspects of shape, weight, and efficiency, a lamp controller called a high frequency lighting type ballast (inverter type ballast) comes into use in the present fluorescent appliances, and is also being used in HID lamp (mercury lamp, metal halide lamp, etc.) appliances, bulb type fluorescent lamps, etc.
This inverter type ballast has advantages in that it has high efficiency and is able to save electric power, and it is also able to reduce lamp flickering and ballast noise, and furthermore, it is able to reduce its weight. For these reasons, inverter control of the above-mentioned fluorescent lamp appliances has made rapid progress.
However, in the above-mentioned high-frequency inverter or inverter type ballast (hereinafter referred to as an “inverter”), a capacitor smoothing circuit method for full-wave rectification, which employs rectifiers (diodes) and performs smoothing with an electrolytic capacitor, is often used, and distorted-wave current resulting from diode nonlinearity flows in a commercial power supply.
For that reason, a harmonic component (harmonic current) flows in an input current on the side of a commercial power supply. The problem of failure (harmonic failure) that is affected by this harmonic current has become significant.
For this reason, circuit techniques for suppressing harmonic current have been studied and investigated. For instance, an AC reactor insertion method, a partial smoothing method, an active smoothing filter method (see “Inverter Fluorescent Lamp,” Electronic Technique, Vol.32, No.3, pp.113-119), a dither rectifying method (see “High Power-Factor Switching Regulator Employing Dither Effect,” National Convention Lecture Thesis Collection of Electric Society, No. 546, pp. 5-137), etc., have been proposed.
Furthermore, as an electronic ballast for fluorescent lamps, a neutral-point electronic ballast circuit has been proposed in which a reduction in the harmonic component of an input current on the side of a commercial power supply is performed with only an inverter for lighting a fluorescent lamp, as in the dither rectifying method (see Yoshihito Kato, “One Method of a Simple Harmonic Reduction Circuit,” Electrical Equipment Society Journal, Vol. 12, No. 10, pp. 902-904). A study of the theoretical analysis of this neutral-point electronic ballast circuit (neutral point inverter type ballast) has also been made (see Yoshihito Kato, “Development of an Input Current Low-Distortion Type Electronic Ballast by a Neutral Point Inverter,” Illumination Society Journal, Vol. 79, No. 2, pp. 14-20).
This neutral point inverter type ballast has many advantages in that (1) by inserting a low-pass filter LPF in the side of a commercial power supply, a reduction in the harmonic component contained in an input current is possible with only an inverter for lighting a fluorescent lamp, as in the active smoothing filter method, (2) there is no need to make a new circuit as in the dither rectifying method, and this ballast is applicable to an improvement in the existing half-bridge ballast, (3) the harmonic component of an input current can be reduced to less than IEC standard (IEC 1000-3-2), (4) for an input power factor, a high power factor of 97% or more is obtained, (5) circuit constitution is simple and also a reduction in the luminous efficiency of the lamp is low, and soon. For these reasons, the neutral point inverter type ballast is being used as a suitable circuit that prevents the harmonic failure of an inverter.
FIG. 19
is a basic circuit diagram of a neutral point inverter. This circuit consists of a full-wave rectifier DB that rectifies a commercial power supply Vi to direct-current voltage Ed through a low-pass filter LPF (the constituent diodes in the circuit diagram are represented simply as 1 through 4, and in the specification, they are referred to as DB
1
through DB
4
.), a smoothing capacitor Cs that smooths the output of the full-wave rectifier DB, a series circuit that is connected in parallel with the smoothing capacitor Cs and also consists of voltage-dividing capacitors C
1
and C
2
for dividing direct-current voltage Ed, a series circuit consisting of switching elements Q
1
and Q
2
connected in parallel with the smoothing capacitor Cs, and load RL connected between the connecting point which is between the voltage-dividing capacitors C
1
and C
2
(hereinafter referred to as a “neutral point”) and the connecting point which is between the switching elements Q
1
and Q
2
(hereinafter referred to as a “SW point”). The neutral point is connected to one end of a commercial power supply Vi.
For the operation of this circuit, the ripple voltage included in the output of the full-wave rectifier DB is converted to direct-current voltage Ed with the smoothing capacitor Cs. Then, the switching elements Q
1
and Q
2
are turned on or off to constitute a closed circuit that includes the neutral point. With the closed circuit, the voltage-dividing capacitor C
1
or C
2
is charged from the smoothing capacitor Cs. This charging current becomes load current that flows in the load RL, and reverse current is ensured for an interval during which no load current flows. If the switching elements Q
1
and Q
2
are alternately turned on and off (inverting operation), voltage VL with a high frequency superposed on a commercial frequency will be applied across the load RL. Since the current through the diodes DB
1
through DB
4
has a triangular high frequency with a quiescent interval proportional to load, the current is passed through the low-pass filter LPF to obtain a false sine current waveform. This makes a reduction in the harmonic component of the input current on the commercial power supply possible.
FIG. 20
is a circuit diagram of the case where a fluorescent lamp LT is employed as the load of a neutral point inverter, this circuit being called a neutral point inverter type ballast. Since the load voltage VL that is obtained with only the basic circuit (
FIG. 19
) is a charging-discharging (particularly charging) waveform from both the switching elements Q
1
and Q
2
and the voltage-dividing capacitors C
1
and C
2
, the load voltage VL is unsuitable for lighting of the fluorescent lamp LT. In order to remove this transient portion and in order to make the lamp current a sine wave, a series circuit, which consists of an inductor L
1
and a fluorescent lamp LT, is connected to the load terminal of the basic circuit (between the neutral point and the SW point), and a resonance capacitor is connected in parallel with the fluorescent lamp LT so that it resonates with the fluorescent lamp LT. This circuit constitution (load circuit) is the circuit shown in
FIG. 20
(hereinafter referred to as an “implementation circuit”). A description will hereinafter be given of the operation of this implementation circuit. When a smoothing capacitor Cs has a sufficiently larger value than voltage-dividing capacitors C
1
and C
2
(Cs>>C
1
, C
2
), the voltage of the maximum value Vm of an input voltage (Vi=Vm·sin(wt)) is obtained across the smoothing capacitor Cs (Vm=Ed). This is because although the rectifier DB and the voltage-dividing capacitors C
1
and
Ebato Koji
Kato Yoshito
Okutsu Kenzo
Nippo Electric Co., Ltd.
Nixon & Peabody LLP
Studebaker Donald
Vu David
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