Electric lamp and discharge devices: systems – Periodic switch in the supply circuit – Plural periodic switches or multiple contact periodic switch
Patent
1988-01-25
1990-07-31
Laroche, Eugene R.
Electric lamp and discharge devices: systems
Periodic switch in the supply circuit
Plural periodic switches or multiple contact periodic switch
315219, 315DIG7, H05B 4129
Patent
active
049452894
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to electronic supply systems for fluorescent tubes with electrodes and, more particularly, to electronic supply systems for fluorescent tubes with electrodes that allow virtual instantaneous ignition and energy savings.
2. Description of the Prior Art
The majority of fluorescent tubes currently in use are supplied by a system which has several shortcomings. Two major shortcomings are high energy consumption and rapid tube deterioration. These prior art assemblies comprise a reactance and use the opening of a bimetallic strip to energize a gaseous mixture located between filaments in the tube. Because ignition is rarely instantaneous, several openings of the bimetallic strip are generally required. These repeated openings cause the tube to flicker, which is detrimental to its service life. Further, the reactance consumes a large amount of energy which causes it to heat. Still further, the reactance introduces a large amount of reactivity into the mains line, which increases consumption proportionately.
Research has been carried out with a view towards producing a supply system using only semi-conductor components and transformers so as to consume very little energy and so as to allow instantaneous ignition.
One design, among others, is illustrated in French Specification No. 2,520,575. This design uses two series-mounted transistors which amplify a square signal supplied by an auxiliary frequency generating circuit and transmit it to a series oscillating circuit comprising a coil L1, a lighting unit and a charge capacitor C3.
This system was rapidly improved by omitting the related frequency-generating circuit and by replacing it with a transformer which receives a sinusoidal signal from the oscillating series circuit and uses it to control the two transistors. This system, which is simple in design and is illustrated in French Specification FR No. 2,478,933, has two disadvantages. First, its start-up is random and second, short periods during which the transistors simultaneous allow passage of current are possible. During such periods, the lighting unit is extinguished as it no longer receives a supply and the transistors are traversed by high intensity current which is harmful to their service life.
Various patents providing solutions to the above-mentioned problems have been filed. Three of them, specifications EP No. 0171108, DE No. 3,412,944 and WO No. 87/00719, are discussed in some detail below.
Certain start-up of a circuit is attained, for example, by transmitting a starting pulse to one of the transistors. This is effected by means of a breakdown element, or diac, connected on the one hand to the base of the transistors whose emitter is grounded and on the other hand between a capacitor and a resistor connected in series between the supply terminals and constituting a time base. Thus, once the voltage of the capacitor terminals is higher than the sum of the emitter to base voltage of the transistor and the breakdown voltage of the diac, the diac allows the starting pulse to pass through. However, as the charging capacitor of the LC series circuit is generally grounded, it is imperative that the series circuit has been charged before the transistor which short-circuits it allows current to pass due to the pulse from the diac. This requires an additional system which allows the series circuit to be precharged during the voltage increase of the time constant capacitor. This complicates the general circuit. Thus, a resistor 51 short-circuits the transistor 11 in specification EP No. 0171108; a special arm comprising a diode 17 and parallel connection of a capacitor 19 and resistor 21 controls a switch 14 allowing a capacitor 15 to charge through a capacitor 18 in specification WO No. 87/00719; and a weak charging current passes through a diode 31 and a resistor 32 in specification DE No. 3,412,944.
The problem of overlap in the conducting time of the bipolar transistors is caused by the fact that the time for passage
REFERENCES:
patent: 3890537 (1975-06-01), Park et al.
patent: 4398128 (1983-08-01), Wallank
patent: 4481460 (1984-11-01), Kroning et al.
patent: 4527098 (1985-07-01), Owen
patent: 4562383 (1985-12-01), Kerscher et al.
Interpatents Ltd.
LaRoche Eugene R.
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