Starting and operating circuit for gaseous discharge lamps

Abstract

Operating circuits for gaseous discharge lamps, such as those of metal vapor type, having ballast devices of conventional type are provided with high voltage generating means for applying high voltage starting pulses on the lamp. The circuits comprise a charging capacitor and a voltage sensitive switch device forming a series discharge loop with a selected number of turns of the ballast coil winding at its output end, a resistor in series with the capacitor, and a choke coil in series with the resistor to provide improved ignition voltage and energy for starting lamps of relatively low operating voltage.

Parent Case Text

This application is a continuation-in-part of co-pending application Ser. No. 674,508 filed Oct. 11, 1967, now abandoned, and assigned to the same assignee as the present invention.

Description

The present invention relates to discharge lamp operating and starting circuits and especially to discharge lamps requiring a starting voltage substantially higher than the operating voltage.

It is an object of the invention to provide a simple, reliable, and economical starting and operating circuit for gaseous discharge lamps which require high starting voltages.

It is a particular object of the invention to provide a starting and operating circuit for discharge lamps of the above described type which have relatively low operating voltage and input voltage from which it is relatively difficult to generate high ignition voltage.

It is still another object of the invention to provide a starting circuit of the described type which is slaved to the lamp instantaneous ignition requirements and which automatically ceases operation once the lamp has started.

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

With the above objects in view, the present invention relates to a starting and operating circuit for gaseous discharge lamps comprising a source of alternating current, ballasting means connected at its input side to the alternating current source, discharge lamp means connected to the output side of the ballasting means, and high voltage starting means including a portion of the ballasting means connected to the latter at it output side for providing a high voltage starting pulse on the discharge lamp means, the high voltage starting means comprising a charging capacitor and a resistor connected in series across the discharge lamp means, voltage sensitive switch means having a predetermined breakdown voltage connected across the charging capacitor and the portion of the ballasting means and forming a series discharge loop therewith for generating high frequency starting pulses, and induction means connected in series with the charging capacitor and the resistor for providing effective impedance to the high frequency starting pulses generated by the series discharge loop.

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

FIG. 1 is a circuit diagram of a lamp starting and operating circuit in which the invention is embodied; and

FIG. 2 is a circuit diagram of a modification of the FIG. 1 circuit.

Referring now to the drawing, and particularly to FIG. 1, there is shown a starting and operating circuit for a gaseous discharge lamp 1, such as a sodium or other metal vapor 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 line conductors 3 and 4 across terminals 2 of an alternating current source, with inductive reactance ballast 5 connected in series therewith to provide a current limiting impedance, as is conventional in discharge lamp circuits. In order to provide high voltage starting pulses, e.g., of 2 or 3 kilovolts, on lamp 1, there is provided in the FIG. 1 embodiment a high voltage pulse generator comprising capacitor 6 and resistor 7 connected in series across lamp 1 on the output side of reactor 5, and a voltage sensitive symmetrical switch 8, such as a neon glow lamp, which is a bi-laterally conducting gas tube and which becomes conductive only upon application of a predetermined voltage thereon. Other types of voltage sensitive bi-laterally conducting switch devices may be used instead of a neon glow lamp, as, for example, oppositely poled parallel connected controlled rectifiers, Shockley diodes, triacs (a-c semiconductor switch with single control electrode) or other equivalent switch devices or circuits. As shown, glow lamp 8 is connected across capacitor 6 and a predetermined number of turns 9 of reactor ballast 5 at the output end thereof, so that glow lamp 8 is in series discharge relation with capacitor 6 and the tapped turns 9 of ballast 5 in series therewith.

The number of turns thus tapped off at the output end should be sufficient to completely couple in an auto-transformer action the high voltage across the entire winding of reactor 5. The actual number of turns involved dictates the pulse inductance of the discharge loop. If the inductance is too small, the peak current in the discharge loop is too large, resulting in high resistance voltage drops around the loop and high switch losses, thus lowering the high voltage magnitude and energy level applied to lamp 1. In a typical arrangement in the embodiment illustrated, the ratio of total turns to tapped turns selected may be about 30 to 1, which usually suffices to provide good coupling and adequate peak output voltage for starting lamp 1.

Connected across terminals 2 at the input side of reactor ballast 5 is capacitor 10 which serves both as a high frequency by-pass and a power factor improvement capacitor. Such a capacitor, however, is not always necessary.

In the operation of the described circuit, capacitor 6 is initially charged through resistor 7 by the input voltage from the alternating current source. As the voltage across capacitor 6 rises, it reaches the breakdown potential of neon glow lamp 8. When this occurs, capacitor 6 discharges through tapped turns 9 placing, say, 275 volts across those turns, resulting in a step-up by reactor 5 acting as a pulse transformer to a voltage of, say, about 3300 volts which appears across the total reactor turns. Pulses of this high voltage level are thereby produced across lamp 1 by the pulse generating circuit described. The line side of reactor 5 is shorted at the pulse frequency by capacitor 10. Since the pulse voltage cannot rise across capacitor 10, it must rise across resistor 7. Hence the pulse voltage appears across discharge lamp 1 in the correct polarity on each half cycle until lamp 1 starts. Upon starting of lamp 1, the pulsing mechanism is disabled as a result of the voltage clamping action of the ignited lamp load and therefore the voltage buildup across capacitor 6 does not reach the breakdown level of neon lamp 8.

In the use of a circuit such as thus described, a difficulty is encountered where lamp 1 is of a type which has a relatively low operating voltage, such as a 150 watt high pressure sodium vapor lamp of known type, as compared to 400 watt or 250 watt gaseous discharge lamps of the same type. Whereas the 150 watt lamp has an operating voltage of about 55 volts, and in the circuit shown should have relatively low open-circuit-voltage such as 110 volts to provide stable lamp operation, the 400 watt and 250 watt lamps have operating voltages of about 100 volts and are typically operated at open-circuit-voltages of 208 volts or more. Where a low operating voltage lamp such as described is used, it is not feasible in the described circuit to adjust the value of resistor 7 in order to provide the necessary high voltage to ignite the lamp. Thus, if the value of resistor 7 is made relatively low in order to charge capacitor 6 to a sufficiently high voltage to start the lamp, the resistor constitutes a load on the circuit which reduces the ignition voltage to an excessively low level which is insufficient to start the lamp. On the other hand, if resistor 7 has too high a value, capacitor 6 does not become charged to a sufficiently high level to start the lamp.

In accordance with the present invention, these problems are overcome by placing an inductor 11, specifically a radio frequency choke (RFC) coil, in series with resistor 7 as shown in FIG. 1. Inductor 11 presents a high impedance to the high frequency starting pulses generated by operation of the described series discharge loop, and as a result sufficient impedance is provided during that operation to prevent undue loading of the starting pulse. Furthermore, inductor 11 exhibits a low impedance to the 60 cycle current charging capacitor 6, and thus allows the capacitor to charge to the desired level.

In general, the described circuit is particularly useful for lamps having an operating voltage of about 45 to 65 volts, and wherein the open circuit voltage across the lamp is about 105 to 125 volts.

FIG. 2 shows the invention as employed in a lamp operating circuit having a different high voltage generating circuit. In this embodiment, a triac 12 replaces neon tube 8 and its control (gate) electrode 12a is connected to a voltage sensitive triggering device 13, such as the silicon bi-lateral switch (SBS) shown, or a bi-lateral trigger diode (diac). The firing of triac 12 is controlled in the illustrated embodiment by a circuit comprising resistor 14 and resistor 15 connected in series across triac 12, with SBS 13 connected to the junction of resistor 14 and resistor 15, and capacitor 16 connected across resistor 15, so that triac 12, its gate electrode 12a, SBS 13 and capacitor 16 form a series discharge loop. This circuit provides for proper phase control of the triac firing so that the starting pulses occur at the optimum time in the alternating current cycle, it being understood by those skilled in the art that the timing of the trigger operation will be dependent upon the relative values of resistor 14 and resistor 15.

In a typical circuit such as shown in FIG. 2, the components listed below will have the following values:

Triac 12 RCA No. 40669 SBS 13 GE No. 2N4992 Capacitor 16 0.12 mfd .+-. 5%, 100 VDC Resistor 14 68K ohms .+-. 5%, 1/2W Resistor 15 5.6K ohms .+-. 5%, 1/2W Capacitor 6 0.47 mfd .+-. 10%, 400 VDC Resistor 7 3.3K ohms .+-. 5%, 5W RFC coil 11 12 mh, 35 ma Ballast 5 30 ohms, 3.3 amps, 247 turns total Ballast turns 9 8 turns

While the invention has been described in connection with the use of bi-lateral (symmetrical) switches for providing starting pulses on each half-cycle it will be understood that, where desired or appropriate for providing starting pulses only on alternate half-cycles, a unidirectional switch such as an SCR may be used in place of triac 12, and a unidirectional trigger device such as a Shockley diode would then be used in place of SBS 13.

It will also be understood that the positions of capacitor 6 and switch 8 may be interchanged in appropriate situations where this is desired.

It will further be understood that various forms of inductive ballast devices could be used in the described circuit instead of the reactor ballast shown, as for example, the ballasts shown in the aforementioned co-pending application, and accordingly the disclosure of the latter application relating to such other ballasts and associated parts is incorporated by reference herein.

Although the invention has particular utility where lamps of relatively low operating voltage are used, other types of lamps may be employed in the described circuits even though they operate at substantially higher voltages.

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.

Claims

What I claim as new and desired to secure by Letters Patent of the United States is:

1. A starting and operating circuit for gaseous discharge lamps comprising a source of alternating current, ballasting means connected at its input side to said alternating current source, discharge lamp means connected to the output side of said ballasting means, and high voltage starting means including a portion of said ballasting means connected to said ballasting means at its output side for providing a high voltage starting pulse on said discharge lamp means, said high voltage starting means comprising a charging capacitor and a resistor connected in series across said discharge lamp means, voltage sensitive switch means having a predetermined breakdown voltage connected across said charging capacitor and said portion of said ballasting means and forming a series discharge loop therewith for generating high frequency starting pulses, and induction means connected in series with said charging capacitor and said resistor for providing rapid charging of said charging capacitor and effective impedance to the high frequency starting pulses generated by said series discharge loop.

2. A circuit as defined in claim 1, said ballasting means comprising inductance coil means having a plurality of turns, said portion of said ballasting means comprising a predetermined number of turns of said inductance coil means at its output side, said inductance coil means stepping up the voltage produced across said predetermined number of turns by operation of said discharge loop.

3. A circuit as defined in claim 1, said induction means comprising a radio frequency choke coil.

4. A circuit as defined in claim 3, said voltage sensitive switch means comprising a controlled semiconductor switch having a control electrode, and voltage sensitive trigger means connected to said control electrode and said charging capacitor for triggering the operation of said controlled switch.

5. A circuit as defined in claim 4, wherein said switch means comprises a bi-lateral conducting switch and said triggering means comprises a voltage sensitive bi-lateral conducting device.

6. A circuit as defined in claim 4, said trigger means comprising a circuit for triggering the operation of said controlled switch at a predetermined time in each cycle, said circuit comprising resistance means connected across said switch means, a voltage sensitive trigger device connected to said control electrode and said resistance means, and capacitance means connected to said trigger device and said switch means so as to form a series discharge loop therewith.

7. A circuit as defined in claim 1, including a high frequency by-pass capacitor connected across said alternating current source on the input side of said ballasting means.

8. A circuit as defined in claim 1, wherein said discharge lamp means comprises a lamp having an operating voltage of about 45 to 65 volts.

9. A circuit as defined in claim 8, wherein the open-circuit-voltage across said lamp is about 105 to 125 volts.