GB2139022A - Ballast circuit for lamps with low voltage gas discharge tubes - Google Patents

Abstract

The circuit operates directly from an applied 220 volt, 50 Hz or 120 volt, 60 Hz A.C. voltage source and comprises a capacitor C1 connected serially with both an incandescent filament and the gas discharge tube. If desired, the incandescent filament may be replaced with a resistive element. The value of the capacitor is selected so as to reduce the applied 220 volt, 50 Hz or 120 volt, 60 Hz A.C. source to a desired range for operating the circuit in a manner to develop a desired reduced voltage for operation of the gas discharge tube. The reduced operating voltage correspondingly reduces the restrike voltage that may be necessary to operate the gas discharge tube during restrike conditions. The reduced operating voltage of the gas discharge tube readily allows for the development of the restrike voltage directly available from the typical 220 volts, 50 Hz or 120 volts, 60 Hz A.C. source. The circuit arrangement further provides for an automatic restrike voltage under reduced voltage A.C. source conditions, a voltage developed across the capacitor C1 then being additive with the A.C. source voltage to form the restrike voltage (Fig. 7). <IMAGE>

Description

SPECIFICATION Ballast circuit for lamps with low voltage gas discharge tubes The present invention relates to a ballast circuit for a gas discharge lamp. More particularly, the present invention relates to a ballast circuit operated directly from an alternating current (A.C.) voltage source and having a capacitor serially connected to a serially arranged incandescent filament and a gas discharge tube.

Recent improvements to the incandescent art have provided an improved lighting unit having a highly efficient gas discharge tube as the main light source and an incandescent filament as a supplementary light source. Such an improved incandescent lamp is generally described in U.S. Patent 4,350,930, of Piel et al, issued September 21, 1982.

The gas discharge tube has various modes of operation such as, (1) an initial high voltage breakdown mode, (2) a g low-to-are transition mode, and (3) a steady state run mode. One of the circuit performance parameters is that the voltage applied across the gas discharge tube be such that the current flowing within the gas discharge tube is maintained above a critical value such as 60 milliamps. If the current flowing in the gas discharge tube drops below this critical value the arc condition of the gas discharge tube may extinguish, which, in turn, may cause the gas discharge tube to revert from its steady state run mode to its glow-to-transition mode or even to the initial breakdown mode.The reestablishment of the desired arc condition of the gas discharge tube may require a restrike voltage having a voltage value typically about 2.5 times or more than that of the operating voltage of the gas discharge tube.

The restrike voltage necessary for a gas discharge tube of 2.5 times its operational voltage presents a difficulty for a ballast circuit for a discharge tube operating directly from a 120 volt, 60 Hz A.C. source. For example, if the gas discharge tube has an operating voltage of 80 volts A.C. a restrike voltage of 80 x 2.5 200 volts or more is typically necessary and which voltage value is not ordinarily available from the peak-voltages of a typical 120 volt, 60 Hz A.C. source, It is considered desirable to provide means for reducing the operating voltage of a gas discharge tube, which, in turn, reduces the value of the necessary restrike voltage, which, in turn, more readily allows development of the restrike voltage from the peak voltage value of a typical 120 volt, 60 Hz A.C. source, which, in turn, more readily allows the ballast circuit to operate the gas discharge tube directly from a 120 volt, Hz A.C. source.

A further difficulty involved with a ballast circuit is its ability to adapt to changes in the voltage and frequency parameters of the A.C. source. The voltage and frequency parameters are determined by the available power source. For example, the circuit parameters of a ballast circuit are typically selected for the applied A.C. source so that a ballast circuit operating with an applied A.C. source of 120 volts, Hz does not perform in a successful manner when the applied A.C. source is changed from a 120 volt, 60 Hz A.C. source, typically available for United States utilization, to a 220 volt, 50 Hz A.C. source typically available for European utilization and elsewhere in the world.It is considered desirable to provide a ballast circuit for a gas discharge tube operable directly from either a 120 voit, Hz A.C. power source or with suitable component selection for a 220 volt, 50 Hz power source.

Accordingly, objects of the present invention are to provide such a ballast circuit, particularly one capable of operating directly from various alternating current (A.C.) sources to provide a desired operating voltage for a gas discharge tube having a serially connected incandescent tungsten filament.

In one embodiment of the invention there is provided a lighting unit having a gas discharge tube as the main light source, and a filament serving both as a resistive element and as a supplementary light source.

The filament is in serial arrangement with the gas discharge tube as is a starting circuit and a capacitor. The resistive-capacitive ballast circuit is adapted to accept various applied alternating current (A.C.) voltages across its terminals. The ballast circuit develops A.C. operating voltage for the gas discharge tube. The ballast circuit comprises a capacitor serially connected between one of the terminals receiving the applied A.C. voltage and the serial arrangement of the filament and the gas discharge tube. The capacitor is selected to have a value so as to reduce the A.C. voltage which is applied across the gas discharge tube and filament combination by a factor in the range of about 3 to about 1.

In the accompanying drawings, by way of example only: Figure 1 shows a lighting unit embodying the present invention; Figure 2 is a circuit arrangement for the unit of Figure 1; Figure 3 is similar to Figure 2 and shows an alternative circuit arrangement.

Figure 4 shows a circuit arrangement for a gas discharge tube and a serially arranged filament connected directly to an A.C. source.

Figure 5 is a chart showing the waveform related to the circuit operation of Figure 4; Figure 6 is a chart showing the voltage related to the operation of the circuit arrangement of Figure 3 applicable for an applied 220 volt, 50 Hz A.C. source; and Figure 7 is a chart showing the voltage related to the operation of the circuit arrangement of Figure 3 in response to a reduced 220 volt, 50 Hz A.C. source.

Figure 1 shows a lighting unit 10 having a gas discharge tube (shown in phantom) as the main light source, a filament as a supplementary light source (also shown in phantom) spatially disposed within a light-transmissive outer envelope 12. The lighting unit 10 has an electrically conductive base 14 and a housing 16 for lodging the electrical components of the lighting unit 10. Figure 1 further shows the housing as confining a resistive ballast circuit 20 shown more clearly in Figure 2.

Fioure 2 shows the circuit arranqement of a resistive-capactive ballast circuit 20 for the lighting unit 10 wherein the filament provides the resistive element. If desired, the filament may be replaced by a resistor.

The ballast circuit 20 of Figure 2 is operable from an alternating current (A.C.) source of either 120 volts, Hz or of 220 volts, 50 Hz applied across its first and second terminals L1 and L2 each having an appropriate connection (not shown) to the electrically conductive base 14. The ballast circuit 20 develops an A.C.

operating voltage for the gas discharge tube having a starting circuit 22. The gas discharge tube is serially arranged with the tungsten filament as shown in Figure 2. The gas discharge tube may be of the highly efficient type described in U.S. Patent 4,161,672 of D. M Cap and W. H. Lake, issued July 17, 1979.

The ballast circuit 20 has various typical parameters and typical component values given in Table 1 which are selected for operation with either a typical A.C. applied source of 120 volts at 60 Hz or a typical A.C.

applied source of 220 volts at 50 Hz.

TABLE 1 Parameter/ Component 120V 220V Value 60 Hz 50 Hz C1 40wiz 10af Lamp operating 25 Volts 60 Volts Voltage "Lamp Power Input 62 watts 51.5 watts (PIN) to ballast circuit 20 Power (PLamp) 33.0 watts 33.8 watts applied to gas discharge tube Current (Id 1.7 amps 1.0 amps (R.M.S.) of gas discharge tube Circuit Efficacy approximately approximately (PLamp/PIN) 0.53 0.65 The lamp operating voltage V,amp of Table 1, and Table 3 to be discussed, is the value of voltage observed across the gas discharge tube only when the gas discharge tube is conductive.

The resistive-capacitive ballast circuit 20 is serially arranged between terminal L1 having the applied A.C.

voltage source and the serial arrangement of the filament and the gas discharge tube having the starting circuit 22. Figure 1 shows the arrangement of the starting circuit 22 as comprised of a plurality of conventional elements of the type indicated or having typical component values both as given in Table 2.

TABLE 2 120V 220V Value or Type Value or Type Element (120 VAC) (220 VAC) Qs SIDAC type K1 20 of SIDAC type K240 Cs Capacitor 0.05 ijf Capacitor 0.05 f Ts Autotransfdrmer Autotransformer construction using construction using a pair of Ferroxcube a pair of Feroxcube type 813E187-3E2A type 813E187-3E2A E Cores and a type E Cores and a type 990-023-01 bobbin 990-023-01 bobbin wound with a 20 turn wound with a 20 turn primary and a 400 primary and a 400 turn secondary turn secondary Rs Resistor having a Resistor having a value of 15KQ and value of 50KQ and a a rating of 1 watt rating of 1 watt The starting circuit 22 provides the necessary voltages so as to transition the gas discharge tube discharge from its (1) initial state requiring a high applied voltage to cause an initial arcing of the gas discharge tube, (2) to its glow-to-arc mode, and then (3) its final steady state run condition. The starting circuit 22 operates in the following manner, (1) when the gas discharge tube is initially energized it is a relatively high impedance device so that the current initially flows through Rs charging Cs, (2) when the voltage on capacitor Cs equals or exceeds the breakdown or turn-on voltage (approximately 120 volts) of the S!DAC Qs, connected in a parallel manner across Cs, via a ferrite transformer Ts, Q5 is rendered conductive, (3) the conductive Qs provides a low impedance path so that the energy stored on capacitor Cs is suddenly discharged, through the primary of Ts which produces a potential sufficient for ionization of the gas discharge tube, (4) this discharge energy is of a sufficient magnitude to cause an initial arcing condition of the gas discharge tube, (5) the gas discharge tube then sequences from its inital state to its glow-mode and finally to its steady-state run mode, (6) when the gas discharge tube is in its steady state run condition it becomes a relatively low impedance and low voltage device so that the current is preferentially directed to the gas discharge tube, and finally (7), the starting circuit 22 is effectively removed from the ballast circuit 20 since the conducting lamp prevents the voltage on Cs from reaching the turn on voltage of the SIDAC. The ballast circuit 20 with the starting circuit 22 removed is shown in Figure 3.

The circuit arrangement 20 of Figure 3 provides a ballast circuit for developing A.C. operating voltage for the gas discharge tube. The ballast circuit 10 is comprised of a capacitor C1 and allows operating directly from an A.C. source having typical parameters of 120 volts, 60 Hz or 220 volts, 50 Hz with the appropriate selection by parameters and component values given in Table 1. The capacitor C1 is of substantial importance to the present invention in that it provides a means for reducing the A.C. operating voltage of the gas discharge tube to desired values, which, in turn, reduces the amplitude restrike voltage to desired values that may be necessary under restrike conditions, which, in turn, allows for the restrike voltage to be developed from the A.C. source.Further, the capacitor C1 by storing a charge during the time duration when the gas discharge tube is non-conducting, provides a voltage which is additive to the line voltage both of the voltages being used to promote restrike of the gas discharge tube. Additionally, the capacitor C1 adapts the operation of the gas discharge tube to either a 120 volt, 60 Hz source or a 220 volt, 50 Hz source. In order that the ballast circuit 20 of the present invention may be more clearly appreciated reference is now made to the circuit of Figure 4 which does not incorporate the present invention.

Figure 4 shows the A.C. source directly applied to the serial arrangement of the filament and gas discharge tube. Figure 4 further shows the points A and B located on either side of the filament and a point C located on one end of the gas discharge tube which is connected to the A.C. source. The voltage between points A and C which is the voltage of the A.C. source and is herein termed VAC, Similarly, the voltage between points B and C which is the voltage applied across the gas discharge tube is herein termed Vc. The voltage VAC iS divided between the serially arranged filament and operating gas discharge tube. The division of VAC jS determined by the voltage of the operating gas discharge tube with the remaining voltage appearing across the filament.

The voltage across the filament of Figure 3 is herein termed VAs. Reference is now made to Figure 5 showing the voltages VAC, Vec and VAB, shown in hatched representation between VAC and VAS, for the circuit arrangement of Figure 4.

Figure 5 shows the amplitude of the voltage VAC, Vsc and VAB along its Y axis and repetitive duration or time of the voltages VAC, VBC and VAB along its X axis. Figure 5 is related to an applied A.C. voltage having a typical value of 220 volts and a frequency of 50 Hz.

From Figure 5 it is seen that Vac has a peak amplitude of about 250 volts. This amplitude corresponds to an operating voltage for the gas discharge tube of approximately 100 volts. As discussed in the "Background" the restrike voltage of the gas discharge tube that may be necessary under restrike conditions of the gas discharge tube is typically 2.5 times that of the opration voltage of the gas discharge tube so that an operation voltage of 100 volts would require a restrike voltage of approximately 250 volts.While such a restrike voltage of 250 volts is available from being directly derived from the A.C. source voltage VAC having a peak value of approximately 310 volts, the circuit arrangement of Figure 4 having the waveforms of Figure 5 has an undesirable efficiency rating relative to the values of voltages VAB and Vac of the filament and gas discharge tube respectively. The waveforms of Figure 5 are meant to show that area occupied by VBC (voltage across the gas discharge tube) is only about 30% of VAC (source voltage).

The area of VAB relative to the area of VAC represents that about 200 volts of the A.C. voltage VAC iS used to maintain excitation of the filament, whereas, the area of Vac is means to represent that only about 100 volts of the A.C. voltage is used to maintain excitation of the gas dishcharge tube. It is desired that the great majority of the voltage VAC be used for the primary light source gas discharge tube, and conversely, a minor amount of the voltage VAC be used for the supplementary light source filament. The ratio of VAC between the gas discharge tube and filament is a measurement of the ballast circuit efficiency and the waveform VAS, VBC and VAC of Figure 5 represent a relative low circuit efficiency of about 30%.Similar manipulations for the operating voltage, the restrike voltage, and peak values available from an A.C. source of 120 volts at 60 Hz would render the circuit arrangement of Figure 4 undesirable for direct operation from an A.C. source of 120 volts at 60 Hz.

The disadvantages of the circuit arrangement of Figure 4 are overcome by the circuit arrangement of the present invention shown in Figure 3. Figure 3 is structurally similar to Figure 4 with the exception that the capacitor C1 is connected between the A.C. source and the serial arrangement of the filament and gas discharge tube. Figure 3 shows points A, A' located on opposite sides of capacitor C1, point B arranged between the filament and one end of the gas discharge tube and point C located at the other end of the gas discharge tube which is also connected to the A.C. source. The voltages related to the Figure 3 are herein indicated and shown in Figure 6.

Figure 6 is segmented into four sections, (1) Figure 6(a) showing VAC which is the A.C. source voltage having peak values of about 300 volts, (2) Figure 6(b) showing VAA, which is the voltage across the capacitor C1 having a peak value somewhat less than 300 volts, (3) Figure 6(c) showing, (a) VA'C which is the voltage applied across the filament and gas discharge tube having a peak value of about 200 volts, (b) VBC (partially shown in phantom) which is the voltage applied across the gas discharge tube having a peak value of about 200 volts, and (c) VA'B which is the voltage applied across the filament and is shown in Figure 6(c) as a hatched representation between VA'C and Vac, and (4) Figure 6(d) showing ld which is the current flowing through the arc discharge tube.

The voltage Vac of Figure 6(c) has a relatively low peak value, such as approximately 110 volts, compared to that of Vac of Figure 5. This peak amplitude of 110 volts corresponds to an operating voltage for a gas discharge tube of approximately 60 volts. As discussed in the "Background" section and Figure 5, the operating voltage typically necessitates a restrike voltage of 2.5 times that of the operating voltage.

However, an operating voltage of 60 volts developed by the circuit arrangement of Figure 3 only necessitated a restrike voltage of 150 volts. Such a restrike voltage of 150 volts is readily available from being directly derived from the A.C. source voltage VAC of Figure 6 having a peak value of 310 and is well within the limits desired for the restrike voltage. The lower restrike voltage provided by the circuit arrangement of Figure 3 relative to Figure 4 allows the ballast circuit of the present invention to be directly operated from an A.C.

source of 220 volts at 50 Hz in a desirable manner. Similar manipulation for the operating voltage, restrike voltage, and peak values available from an A.C. source of 120 volts at 60 Hz would show the circuit arrangement of Figure 3 directly operable from an A.C. source of 120 volts at 60 Hz in a desirable manner.

The related waveforms of the circuit arrangement of Figure 3 along with the associated description for having an applied A.C. source of 220 volts at 50 Hz are essentially the waveforms and associated description of Figure 6 with the waveforms being scaled down by a factor of about 2 to 1 so as to show and describe the circuit operation of Figure 3 for an applied 120 volts, 60 Hz source.

Still further, the circuit arrangement of Figure 3 having the waveforms of Figure 6 has a desirable efficiency rating relative to the values of the voltage VA'B and Vac of the filament and gas discharge tube respectively. In a manner as previously described with regard to the waveforms of Figure 5, the waveforms VARB and Vac of Figure 6 are representative of a relatively high efficiency rating of 0.65.

The circuit arrangement of-Figure 3 provides for the desired operation of the gas discharge tube even in the presence of a relatively low applied voltage that may be experienced during the commonly termed "brown-out" electrical power curtailment conditions. The desired operation of the circuit arrangement Figure 3 in response to relatively low voltage conditions is best described by first referring to Figure 7.

Figure 7 is similar to the previously described Figure 6 and is segmented into, (1) Figure 7(a) showing the voltage VAC having relatively low peak values of approximately 200 volts, (2) Figure 7(b) showing the voltage VAA, having peakvalues of approximately 150 volts, (3) Figure 7(c) showing the voltage VATh having peak values of approximately 300 volts and also showing Vac, and (4) Figure 7(d) showing the current 1d Without the practice of this invention, the relatively low voltage of approximately 200 volts of VAC of Figure 7(a) would be typically insufficient to maintain conduction of the gas discharge tube.

In general, the circuit arrangement of Figure 3, having the waveforms of Figure 7, operates such that the voltage VAA, of Figure 7(b) which is the voltage across the capacitor C1, is preserved when ld = 0 and additive to the input voltage VAC of Figure 7(a) during the next half cycle which voltage VA'C of Figure 7(c) is applied to the filament and gas discharge tube. The operation of the circuit arrangement automatically provides a restrike voltage having a value in excess of the peak value of VAC to the gas discharge tube which inhibits the extinction of the arc conditions of the gas discharge tube under reduced voltage conditions of VAC.The capacitor C1 is charged to nearly the peak value of VAC SO as to form VAA, of Figure 7(b) during the non-conductive state of the gas discharge tube and which becomes additive to VAC. The combined VAA, and VAC forms the restrike voltage to maintain the arc conditions of the gas discharge tube under the reduced voltage condition of VAC of Figure 7(a).

Figure 7 shows, in phantom, two vertical lines 30 and 32 respectively having components 30a 30b,30c,30d, 30e and 32a, 32b' 32c, 32d and 32e. The vertical line 30 and its components is meant to show the initiation of the conductive state of the gas discharge tube during the negative relatively low voltage conditions of VAC, whereas, vertical line 32 and its components is meant to show initiation of the conductive state of the gas discharge tube during the positive relatively low voltage condition of VAC The components 30al 30b, 30c,30d, and 30e are respectively means to represent and show, (1) the negative peak value of VA'C of Figure 7(c) which is the restrike voltage applied to the gas discharge tube under reduced voltage condition of VAC of Figure 7(a) and VA'C has a value of approximately 300 volts, (2) the positive peak value of VAA, of Figure 7(b) which is additive to VAC of Figure 7(a) so as to form the peak restrike voltage of VA'C, (3) the initiation of conduction of the gas discharge tube shown in Figure 7(d) by the negative transition of ld in response to the peak restrike voltage of V'c, (4) the knee of the discharge curve of VA'A of Figure 7(b) representing that the majority of the charge stored on C1 has discharged into the gas discharge tube, and (5) the termination of conduction of the gas discharge tube shown in Figure 7(d) by the positive transition of ld in response to the decay of the restrike voltage of VAC The line 32 and its components 32a 32b,32c,32d, and 32e are meant to represent and show the operation of the circuit arrangement of Figure 3 which causes the positive conduction of current ld of Figure 7(d) during the reduced positive voltage conditions of VAC of Figure 7(a).The description related to line 30 and its components 30a 30b,30c,30d and 30e is respectively applicable to line 32 and its components 32,, 32b,32c, 32d and 32, except for their voltage polarity relationships.

The values of the voltages of Figures 6 and 7 are adaptable to the desired operating voltage and restrike voltages of the gas discharge tube by appropriate selection of the value of the capacitor C1. In a manner as previously mentioned with regard to Table 1, Table 3 lists typical values of C1, relative to the parameters previously discussed hereinbefore, for application with typical values of the applied A.C. voltage VAC.

TABLE 3 VLamp C1 PLamp PIN tod in VAC in Volts in af in Watts in Watts Amperes 115V 25.0 40 33 62 1.7 at60 Hz 115V 25.0 65 51 104 2.3 220V 60.0 10 33.8 51.5 1.0 at50 Hz 220V 65.0 8 26.3 40.4 0.985 at 50 Hz 220V 68.0 6 22.5 34.2 0.504 at50 Hz 220V 68.2 6 21.7 37.8 0.446 at50 Hz 240V 70.0 6 24.5 42.5 0.446 at 50 Hz 260V 70.6 6 27.3 47.9 0.487 at50 Hz 280V 80.0 4 20.0 31.0 0.31 at 50 Hz It should now be appreciated that the lighting unit 10 having the resistive ballast 20 is directly operable from an A.C. source and the A.C. source may be either of 120 volts at 60 Hz or 220 volts at 50 Hz by appropriate selection of capacitor C1. The resistive ballast circuit has a relatively high efficiency rating. The resistive ballast circuit 20 provides such direct operation and develops an A.C. operating voltage for desired performance by the main light source highly efficient gas discharge tube along with desired performance of the supplementary light source filament.

Claims (7)

1. In a lighting unit having a gas discharge tube as the main light source, a filament serving as a resistive element and as a supplementary light source, said filament being in serial arrangement with said gas discharge tube, a starting circu it for said gas discharge tube, and a resistive-capacitive ballast circuit in series with said gas discharge tube, said resistive-capacitive ballast circuit adapted to accept various applied alternating current (A.C.) voltage across its terminals and developing an A.C. operating voltage for said gas discharge tube and filament, said ballast circuit comprising:: a capacitor serially connected between one of the terminals having said applied A.C. voltage and said serial arrangement of said filament and gas discharge tube; said capacitor having a value selected so as to reduce said A.C. voltage in the development of said A.C.

operating voltage of said gas discharge tube and filament combination by a factor in the range of about 3 to about 1.

2. A resistive capacitive ballast circuit according to claim 1 wherein said applied A.C. voltage has values in the range of 115 to 280 volts at frequencies in the range of 50 to 60 Hz and said capacitor has a value selected in the range of about 4 Ff to about 65 us

3. A resistive-capacitive ballast circuit according to claim 1 wherein said ballast circuit develops said A.C.

operating voltage even when subjected to a reduction of said applied A.C. source by a factor of about one-third (1/3).

4. In a lighting unit having a gas discharge tube as the light source, a resistive element in serial arrangement with said gas discharge tube, a starting circuit for said gas discharge tube, and a resistive-capacitive ballast circuit in series with the gas discharge tube, said resistive-capacitive ballast circuit adapted to accept various applied alternating current (A.C.) voltage across its terminals and developing an A.C. operating voltage for said gas discharge tube and filament, said ballast circuit comprising: a capacitor serially connected between one of the terminals having said applied A.C. voltage and said serial arrangement of said filament and gas discharge tube; said capacitor having a value selected so as to reduce said A.C. voltage in the development of said A.C.

operating voltage of said gas discharge tube and-filament combinationn by a factor in the range of about 3 to about 1.

5. A resistive-capacitive ballast circuit according to claim 4 wherein said applied A.C. voltage has values in the range of 115 to 280 volts at frequencies in the range of 50 to 60 Hz and said capacitor has a value selected in the range of about 4 uf to about 65of.

6. A resistive-capacitive ballast circuit according to claim 4 wherein said ballast circuit develops said A.C.

operating voltage even when subjected to a reduction of said applied A.C. source by a factor of about one-third (1/3).

7. A lighting unit substantially as herein described with reference to the accompanying drawings.