Electric lamp and discharge devices: systems – Surge generator or inductance in the supply circuit – Circuit interrupter in the inductance circuit
Reexamination Certificate
1999-02-17
2001-11-27
Wong, Don (Department: 2821)
Electric lamp and discharge devices: systems
Surge generator or inductance in the supply circuit
Circuit interrupter in the inductance circuit
C315S2090CD, C315S2090SC, C315S224000, C315S219000
Reexamination Certificate
active
06323603
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention is directed to control circuits for gas discharge lamps. More specifically, the present invention is directed to a resonant flyback ignitor circuit for igniting gas discharge lamps.
Gas discharge lamps are used in a variety of applications. For example, mercury vapor lamps are used for ultraviolet (UV) curing of ink in printing presses, for curing furniture varnish, in germicide equipment for killing germs in food and its packaging, for killing bacteria in medical operating rooms and for lighting applications such as high intensity discharge (HID) lighting. Many other applications also exist.
A traditional circuit for controlling a mercury vapor lamp includes an AC power source which drives a primary side of a ballast transformer. A secondary side of the transformer is coupled to the lamp. The lamp includes a gas-filled tube with electrodes at each end of the tube. The secondary side of the transformer applies a voltage between the electrodes which accelerates electrons in the tube from one electrode toward the other. The electrons collide with gas atoms to produce positive ions and additional electrons. Since the current applied to the gas discharge lamp is alternating, the electrodes reverse polarity each half cycle.
Collisions between the electrons and the gas atoms generate additional electrons. Therefore, an increase in the arc current causes the impedance of the lamp to decrease. This characteristic is known as “negative resistance.” The lamp is unstable, and current between the electrodes must be limited to avoid damaging the lamp. As a result, a typical control circuit includes a current limiting inductance coupled in series with the lamp. The inductance can either be a physically separate inductor or “built-in” to the transformer as a leakage inductance.
When the lamp is first started, the lamp requires a very large striking voltage to initiate an arc to ionize the gas in the lamp. The electrodes of the lamp are cold and there are almost no free electrons in the tube. The impedance of the lamp is therefore very high. The voltage required to initiate the arc exceeds that required to sustain the arc. For example, the ignition voltage may be 1,000 volts while the operating voltage may be 100 volts. In such cases, a device known as an ignitor has been added to the ballast transformer.
A typical ignitor circuit superimposes high voltage spikes on the normal output voltage produced by the secondary side of the ballast transformer. These high voltage spikes do not provide significant power themselves, but overcome a potential barrier that would otherwise prevent ionization of the plasma in the lamp during each half-cycle of the AC power being delivered to the lamp.
The high voltage ignitor pulses are typically necessary only during the initial ionization and the warm-up period of the lamp. Once the lamp is at its full operating temperature and power, the ignitor pulses are no longer necessary. Most modern ignitors have timers or are biased such that the ignitors become disabled after a certain time period which is determined to be long enough to fully warm-up the lamp.
In one typical igniter circuit, a resistor-capacitor circuit is coupled to the secondary side of the ballast transformer. Before the lamp ignites, the output voltage of the ballast transformer is sinusoidal like the AC voltage applied to the primary side of the ballast transformer. This voltage appears across the resistor-capacitor network. As the voltage rises, more current passes through the resistor, thereby charging the capacitor. The capacitor continues to charge until the voltage across the capacitor reaches a threshold voltage of a bilateral trigger device. At this point, the bilateral trigger device turns on and applies the capacitor across a small portion of the secondary winding. Through transformer action, the voltage on the capacitor is multiplied by the turns ratio in the winding, and a high voltage appears at the output terminals of the ballast transformer.
Since the energy stored in the capacitor is relatively small, and because the transformer is not designed to support large volt-second values, the igniter output appears as a narrow pulse of high voltage on top of the normal output voltage of the ballast transformer. Each pulse usually lasts only a few microseconds. This type of igniter circuit is typically designed to apply several high voltage pulses per half cycle in order to get the lamp ignited. When the lamp does ignite, the lamp clamps the ballast output voltage to a lower value, which thereby limits the amount of charge supplied to the capacitor. Thereafter, the capacitor never reaches the threshold voltage of the bilateral trigger device. This effectively shuts-off the ignitor after the lamp has ignited.
This type of igniter circuit has several disadvantages for gas discharge control circuits that use modulation or phase control to operate the power delivered to the lamp. These circuits require the lamp current to be reliably initiated. Since the energy per pulse is low in conventional igniter circuits, timely lamp ignition is not ensured. Uncertainty in the ignition timing can result in flickering, instability or loss of control of the lamp current. In addition, several voltage pulses are required in succession for reliable ignition. In order to increase the duration of each igniter pulse to ensure ignition, a different approach would be required along with a larger value storage capacitor. Also, the short, low-energy voltage pulses do not propagate well and are therefore limited to applications in which there is a short distance between the igniter circuit and the lamp. Improved ignitor circuits are therefore desired.
SUMMARY OF THE INVENTION
The gas discharge lamp control circuit of the present invention includes a series circuit formed by first and second AC input terminals, an inductance and first and second lamp terminals. An ignitor circuit is coupled to the series circuit and selectively couples and decouples at least a portion of the inductance in parallel with the first and second AC input terminals.
Another aspect of the present invention relates to a method of igniting a gas discharge lamp. The method includes receiving an AC drive signal through first and second AC inputs and applying the AC drive signal to the gas discharge lamp through an inductance which is in series with the gas discharge lamp. At least a portion of the inductance is coupled in a parallel circuit with the first and second AC inputs to store energy from the AC drive signal in the portion. The portion of the inductance is then decoupled from the parallel circuit to generate a flyback voltage in the inductance.
Yet another aspect of the present invention relates to a gas discharge lamp control circuit which includes first and second AC inputs for receiving an AC drive signal and first and second lamp terminals for coupling to a gas discharge lamp. An inductance is coupled in series between one of the first and second AC inputs and one of the first and second lamp terminals. An ignitor circuit couples at least a portion of the inductance in a parallel circuit with the first and second AC inputs to store energy from the AC drive signal in the portion and then decouples the portion from the parallel circuit to generate a flyback voltage in the inductance.
REFERENCES:
patent: Re. 29204 (1977-05-01), Snyder
patent: 3199020 (1965-08-01), Hilker
patent: 3319154 (1967-05-01), Rudge
patent: 3676734 (1972-07-01), Shimizu et al.
patent: 3679936 (1972-07-01), Moerkens
patent: 3699385 (1972-10-01), Paget
patent: 3732460 (1973-05-01), Wattenbach
patent: 3889152 (1975-06-01), Bodine, Jr. et al.
patent: 3922595 (1975-11-01), Vieri
patent: 4179641 (1979-12-01), Britton
patent: 4286193 (1981-08-01), King, Jr. et al.
patent: 4317068 (1982-02-01), Ward et al.
patent: 4351022 (1982-09-01), Dolland et al.
patent: 4415837 (1983-11-01), Sodini
patent: 4663569 (1987-05-01), Alley et al.
patent: 4742276 (1988-05-01), Ku
patent: 4795945 (1989-01-01), Mayer
patent: 4900989 (1990-
Nicollet Technologies Corporation
Vo Tuyet T.
Westman Champlin & Kelly P.A.
Wong Don
LandOfFree
Resonant flyback ignitor circuit for a gas discharge lamp... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Resonant flyback ignitor circuit for a gas discharge lamp..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Resonant flyback ignitor circuit for a gas discharge lamp... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2592143