Starting and Operating Circuit for Gaseous Discharge Lamps

The present invention relates to discharge lamp starting and operating circuits, and particularly concerns such circuits for quickly re-starting extinguished high intensity gaseous discharge lamps while still hot.

Known types of circuits for starting and ballasting high intensity discharge lamps have the disadvantage that when power is briefly removed from the system, the lamp rapidly de-ionizes and ceases to conduct current upon re-application of power. This temporary outage may last from 1 minute up to as much as 15 minutes depending on lamp type and cause interruption of work operations or other activities until the lamp is re-started. In the past, various devices for quickly re-starting the lamp have been suggested, but known devices and circuits of this type have generally been expensive, complicated in structure or unreliable in operation.

In co-pending application of Collins, Ser. No. 201,014, filed Oct. 27, 1980, and assigned to the same assignee as the present invention, there is disclosed and claimed an improved circuit for starting and operating gaseous discharge lamps which quickly re-starts the lamp in the event of a temporary dip or outage of the power supply. In an embodiment of the circuit disclosed therein, an oscillator circuit is employed for producing pulses for immediately restarting the lamp. The present invention relates to a device for improving the operation of the restart oscillator circuit, as more fully disclosed hereinafter.

It is object of the invention to provide an improved device of the above type for starting and operating gaseous discharge lamps, and particularly for quickly re-starting extinguished discharge lamps while still hot.

A further object of the invention is to provide a device of the above type wherein the starting and re-starting circuit automatically ceases operation when the lamp turns on and automatically begins operation when the lamp is extinguished.

Other objects and advantages will become apparent from the following description and the appended claims.

With the above objects in view, the present invention in one of its aspects relates to a starting and operating circuit for gaseous discharge lamps comprising in combination, a source of current, ballast means connected at its input side to the current source, discharge lamp means connected to the output side of the ballast means, first transformer means connected in series between the discharge lamp means and the ballast ballast means, whereby the first transformer means senses flow of current to the discharge lamp means, oscillator means connected at its input side to the current source and at its output side to the first transformer means, the oscillator means producing a high voltage sine wave for starting and restarting the discharge lamp means, the oscillator means comprising second transformer means having a primary winding and a demagnetizing winding, and being connected to the first transformer means, controlled switch means connected to the primary winding, and means for turning off the oscillator means comprising series-connected unidirectional current means and low pass filter means connected at one side to the controlled switch means and at the other side to the second transformer means.

The invention will be better understood from the following description taken in conjunction with the accompanying drawing, in which:

The single FIGURE is a circuit diagram of a discharge lamp starting and operating circuit which comprises an embodiment of the invention.

Referring now to the drawing, there is shown a starting and operating circuit for a high intensity gaseous discharge lamp 1, typically a high pressure sodium vapor lamp or other discharge lamp, which requires a relatively high voltage pulse in order to be ignited and which thereafter operates on a lower voltage. Lamp 1 is connected by conductors 5 and 6 to the output of ballast 7 which in turn is connected to terminals 2 of an alternating current source, typically 120 volts. Ballast 7, which may be any of known types of inductive ballast devices, provides current limiting impedance as is conventional in discharge lamp circuits.

In accordance with the invention, a sine wave oscillator circuit is employed to provide a high voltage high frequency sine wave, e.g., in the range of 1600 to 20,000 Hz, for not only starting lamp 1 when cold but also for quickly re-starting the extinguished lamp while still hot, and there is further provided variable impedance means for reducing the voltage applied to the oscillator circuit should the lamp be inoperative or be absent. For these purposes there is provided in the embodiment shown in the FIGURE, sine wave oscillator circuit 8 connected by conductors 9 and 10 to ballast 7 and variable impedance means in the form of a positive temperature coefficient resistor (PTCR) 11 connected in series between ballast 7 and oscillator circuit 8. As well understood in the art, the PTCR has low resistance when cool and as it gradually heats up due to passage of current therethrough, its resistance correspondingly increases. The particular oscillator circuit illustrated is, in its main construction, of known type, being shown, for example, in U.S. Pat. No. 4,202,031--Hesler et al, (see particularly FIGS. 1 and 7 of the patent and the description relating thereto), the patent being assigned to the same assignee as the present invention. Oscillator circuit 8 comprises full wave rectifier 12 serving as a direct current source, filter capacitor 16, power transistor 17, transformer 18, diodes 19 and 20, resistors 21 and 30 and capacitor 22, the circuit components being connected as shown to provide for turning on and controlling the operation of the transistor, and the combination functioning as a sine wave oscillator. Transformer 18 comprises primary winding 18a, demagnetizing winding 18b and secondary winding 18c, the latter winding, in accordance with the invention, being connected by conductors 33 and 34 to coupling transformer 32, such as the autotransformer shown, connected to conductor 5 in series with lamp 1. Capacitor 36 connected across transistor 17 serves to assure proper transistor commutation over widely ranging load conditions. Transformer 18 also comprises three feedback windings 27, 28, 29 which serve to control the operation of transistor 17. The base of transistor 17 is connected to a starting and control network comprising resistor 30, diodes 19 and 20, feedback windings 28, 29, resistor 21 and capacitor 22. Diode 23 connected to windings 18a, 18b serves to protect transistor 17 from high voltage surges.

Further details of the elements, arrangement and operation of oscillator circuit 8 are set forth in the aforementioned Hesler et al patent, and the description thereof is accordingly incorporated herein by reference.

In accordance with the present invention, an improved device is provided for turning off the restart oscillator circuit during normal lamp operation, thus avoiding lamp flicker, power dissipation and other disadvantages. As shown, this turn-off mechanism comprises series-connected diode 24 and inductor 25 connected at one side to the junction of the anode of diode 23 and transformer demagnetizing winding 18b, and at the other side to the junction of base feedback winding 29 and capacitor 22. This device stops operation of the oscillator during normal lamp operation without interfering with normal restarting functions. This is accomplished with the illustrated circuit by supplying a negative current to the base of transistor 17 which is greater in magnitude than the positive currents supplied by resistor 30 and the feedback windings 28 and 29, and, while the lamp is operating, keeping the oscillator off by supplying a negative current to capacitor 22 which is greater in magnitude than the positive charging current supplied to capacitor 22 through resistor 30. The described turn-off circuit utilizes the high voltage transformer 32 as a lamp current sensor during lamp operation. Transformer 32, which steps up the high frequency voltage to start the lamp, is designed to saturate with the 60 Hz lamp current during normal lamp operation to minimize its interference with lamp current. However, normal transformer action takes place until the current waveform reaches a magnitude sufficient to saturate the core. This produces a 60 Hz voltage on the normal primary of transformer 32. This voltage, being applied to transformer secondary winding 18c, induces a voltage reduced by turns ratio in the other windings of transformer 18. In accordance with the present invention, this voltage is rectified to obtain a negative voltage and filtered, and is employed to turn off transistor 17.

Inductor 25 serves as a high frequency blocking filter to prevent the high frequency restart voltage from turning off transistor 17. Diode 24 serves to block the positive pulse and pass the negative pulse, so as to produce a negative bias to the transistor base for shutting off the transistor.

As indicated, this device operates such that the oscillator is off during normal lamp operation, but as soon as the lamp goes off with power applied, the lamp current feedback pulses stop, capacitor 22 will charge positive through resistor 30 and the oscillator will begin operating.

Instead of being connected to the junction of capacitor 22 and feedback winding 29 as shown, the described diode 24--inductor 25 combination may be connected to the junction of feedback winding 28 and resistor 21, or directly to the base of transistor 17.

While an inductor is shown as the filtering device in the turn-off network, other types of low pass filtering devices may be used instead of an inductor, such as a combination of a resistor and a capacitor.

As disclosed in the aforementioned co-pending Collins application, in the operation of the disclosed circuit, when the circuit is energized, capacitor 16 charges up through PTCR 11 and rectifier bridge 12. During such charging of capacitor 16, PTCR 11 has a current limiting function. After capacitor 16 is fully charged, the oscillator circuit turns on. The RC time constant for capacitor 16 and PTCR 11 is very short, and accordingly capacitor 16 becomes fully charged very quickly, e.g., within one cycle. For oscillator circuit 8 to turn on, capacitor 22 must charge up to a small positive value, such charging being controlled by the RC constant of resistor 30 and capacitor 22 and requiring a number of cycles. The charging capacitor 22 biases the base of transistor 17 positive, and the transistor turns on with the collector current flowing through transformer winding 18a. Feedback windings 28, 29 generate a negative voltage which turns off transistor 17. The energy stored in transformer 18 is then reduced when current flows through the demagnetizing winding 18b of the transformer and diode 23. Oscillator 8 thus becomes free running, as described in further detail in the aforementioned Hesler et al patent, and the output of transformer 18 is a high frequency sine wave. The voltage is then stepped up by coupling autotransformer 32 for application to lamp 1.

Capacitor 35 connected across ballast 7 offers very low impedance to the high voltage generated by transformer 32, and hence very little of the high frequency voltage appears across the ballast.

If lamp 1 starts, the oscillator circuit is turned off by operation of diode 24 and inductor 25, as described previously. Normal starting of a cold lamp is thus provided.

If lamp 1 becomes extinguished due to a dip in the line voltage, the turn off mechanism of diode 24 and inductor 25 ceases to function as a result of a lack of lamp current through transformer 32. Then, since capacitor 16 is still fully charged, it starts to re-charge capacitor 22, which had been held with a small negative charge by the turn-off network, so that a small positive charge is again placed on capacitor 22 and the previously described procedure is repeated for starting lamp 1.

In the event lamp 1 is absent or inoperative, oscillator circuit 8 becomes partially disabled after a predetermined period of operation. This occurs by PTCR 11 becoming heated and presenting a high resistance, thus limiting the output power of the oscillator because capacitor 16 does not become fully charged.

Other details of the structure and operation of the circuit shown in the drawing are disclosed in the aforementioned Collins application.

While the present invention has been described with reference to particular embodiments thereof, it will be understood that numerous modifications may be made by those skilled in the art without actually departing from the scope of the invention. Therefore, the appended claims are intended to cover all such equivalent variations as come within the true spirit and scope of the invention.