CA1155481A - Unitary light source comprising compact hid lamp and incandescent ballast filament - Google Patents

Abstract

49,224 ABSTRACT OF THE DISCLOSURE
Unitary light source comprises compact HID lamp and starting and operating circuit therefor operable from household AC energizing potential. The HID lamp is bal-lasted by incandescent filament means which also provides the major portion of developed light during HID warm up and after power interruption. The ballast filament and input terminals of a full-wave rectifier connect in series across the light source input terminals and the HID lamp connects across the rectifier output. A low-impedance path means and high-voltage pulse generator, which includes a high-voltage electrode operatively associated with the HID lamp, connect across the rectifier input. Initially, the voltage developed across the rectifier input is rela-tively high and the pulse generator and low-impedance path means are responsive thereto to develop high voltage pulses and also provide a low impedance path in series with the ballast filament to cause it to incandesce bright-ly. The developed high voltage pulses applied to the high voltage electrode ionize the atmosphere within the HID
envelope. After the HID lamp starts, the voltage devel-oped across the rectifier input is insufficient to ener-gize the low-impedance path means and pulse generating means. As the HID lamp warms up, the brightness of the incandescent ballast filament means decreases. A lamp keep-alive comprising a DC source is connected across the rectifier means output terminals to provide lamp operating energy during periods of rectifier conduction minima and, if necessary, to provide DC energy as a lamp starting aid.

Description

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1 49,224 UNITARY LIGHT SOURCE COMPRISING COMPACT
HID LAMP AND INCANDESCENT BALLAST FILAMENT

BACKGROUND OF THE INVENTION
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This invention relates to compact light sources and, more particularly, to a unitary light source compris-ing a compact HID lamp and incandescent ballast filament S which are adapted to be operated from a household-type source of AC energizing potential.
HID lamps normally require a short period in which to warm up and build up pressure within the lamp, during which time the light output therefrom is limited.
10 ~ Also, after short periods of power interruption, the HID
lamp normally cannot be reignited until the pressure therein has dropped. A system for supplying light during warm up and after power interruption is set forth in U.S.
Patent No. 3,749,968 dated July 31, 1973 to Jones et al.
wherein a supplemental filament and HID lamp are enclosed within the same outer envelope. When the HID lamp is warming up, or is not operating such as after a period of power interruption, the incandescent filament is operated with full intensity to provide light. After the HID lamp is operating normally, the potential developed across the filament is substantially reduced.
Miniature-type HID metal halide lamps can oper-ate with a high efficacy, as disclosed in U.S. Patent No.
4,161,672 dated July 17, 1979 to Cap et al. and U.S.
25 Patent No. 4,170,746 dated October 9, 1979 to Davenport.

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2 49,224 Various circuits and arrangements for operating such lamps in conjunction with a light-emitting filament which can also serve as a ballast or current limiting impedance for the HID lamp are disclosed in U.S. Patent No. 4,170,744 dated October 9, 1979 to Hansler and U.S. Patent No.
4,151,445 dated April 24, 1979 to Davenport et al. Such lamps are also summarized in New York Times article June 15, 1979, page D3 and Business Week, June ~5, 1979, pages 35 and 36.
SUMMA~Y OF THE INVENTION
There is provided a unitary light source com-prising an HID lamp and t~e light-emitting starting and operating circuit therefor. The light source provides illumination during the warm-up period re~uired for the HID lamp and also after short periods of power inter-ruption when the HID lamp is hot and thus difficult to start. The light source has input terminals which are adapted to be connected to a household-type source of AC
energizing potential. The HID lamp comprises an arc-enclosing envelope having spaced electrodes sealed there-through and operable to sustain a high-intensity-discharge therebetween. An incandescent filament means provides the ballasting for the HID lamp. A full-wave rectifier means has two input terminals and two output terminals and one end portion of the filament ballast connects to one input terminal of the full-wave rectifier, and the other end portion of the filament and the other input terminal of the full-wave rectifier connect across the light source input terminals, with the HID lamp electrodes connecting across the output terminals of the full-wave rectifier. A
low impedance path means and high-voltage pulse-generating means operable from the AC energizing potential connect in parallel with the input terminals of the full-wave recti-fier. When the HID lamp is not operating, the low imped-ance path means is responsive each half cycle of AC ener-gizing potential to a predetermined potential which is developed across the input terminals of the full-wave ' ~

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3 49,224 rectifier in order to be actuated and provide a path of low impedance which parallels the input terminals of the full-wave rectifier. The predetermined potential which actuates the low impedance path means is greater than the maximum potential developed across the input terminals of the full-wave rectifier when the HID lamp is operating.
The pulse generating means has an output terminal consti-tuting a high-voltage electrode which is operatively associated with the HID lamp, and actuation of the low impedance path means triggers the operation of the pulse~
generating means to generate a high voltage of sufficient magnitude to ionize the _atmosphere within the arc enclosing envelope of the HID lamp. There is also pro-vided an HID lamp keep-alive and starting-aid means which has an input connected in circuit with the light source input terminals and an output connected across the output ~ terminals of the full-wave rectifier. Upon initial ener-gization of the light source, the keep-alive means oper-ates to store DC energy of the same polarity as the output of the full-wave rectifier and of a predetermined charge and magnitude sufficient to sustain a discharge in the HID
~ lamp for a short period during the starting thereof, if i required, and also during periods of conduction minima of the full-wave rectifier. The low impedance path means and starting-aid means can be combined into one unit or can be formed as separate units connected in parallel in which case the pulse generator can be actuated just prior to the low impedance path means.
BRIEF DESCRIPTION OF THE DRAWINGS
For a bett,er understanding of the invention, reference may be had to the preferred embodiments, exem~
plary of the invention, shown in the accompanying draw-ings, in which:
Figure 1 is a diagrammatic view of an embodiment of the present unitary light source showing the essential elements thereof and the general circuit arrangement therefor;

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4 49,224 Fig. 2 is a circuit diagram which includes the lamp and ballast filament for the embodiment generally as shown in Fig. l; and Fig. 3 is an alternative and simplified circuit diagram wherein the low impedance path means and pulse generator are consolidated into one unit.
DES~RIPTION OF THE PREFERRED EMBODIMENTS
Referring to Fig. 1, the basic lamp 10 comprises a high efficacy compact HID source 12 comprising an arc-enclosing envelope 14 having spaced electrodes 16 sealedtherethrough and operable to sustain a high-intensity-discharge therebetween. There is also provided an incan-descent tungsten filament ballast means 18 having two end portions 20 and 22a, 22b~ In this embodiment there are provided two ballasting filaments of differing resistance ; so that the unitary light source can be operated at two different levels of illumination. The filament means 18 and HID lamp 12 are both enclosed within an outer light-transmitting envelope 24 which preferably is evacuated. A
full-wave rectifier means 26 has two input terminals 28 and 30 and two output terminals 32 and 34. One end por-tion 20 of the filament ballast means 18 connects to one input terminal 28 of the full-wave rectifier means. The other end portion of the filament ballast means (22a, 22b) and the other input terminal 30 of the full-wave rectifier connect across the unitary light source input terminals 36(a), 36(b) and 38 which in turn are adapted to be con-nected to a household-type source of AC energizing poten-tial, 120V AC 60 Hz.
A high-voltage lamp-starting pulse-generating means 40 is operable from the AC energizing potential and has an output terminal constituting a high-voltage elec-trode 42 terminating proximate the HID lamp 12. The pulse generating means 40 is responsive to application of the AC
energizing potential across the light source input termi-nals 36(a), 36(b) and 38 when the HID lamp is not operat-ing to generate high-voltage pulses which are of sufficient L~
49,224 magnitude to ionize the atmosphere within the arc-enclosing envelope 14 of the HID lamp 12. After the HID lamp 12 is operating, the pulse-generating means is responsive to a lamp-operating parameter, such as the voltage drop there-across, to be rendered inoperative.
A low impedance path means 44 connects in paral-lel with the input terminals 28, 30 of the full-wave rectifier means 26. When the HID lamp is not operating, the low impedance path means 44 is responsive each half cycle of the AC energizing potential to a predetermined potential developed across the input terminals 28, 30 of the full-wave rectifier mea~s 26 to prGvide a path of low electrical resistance which parallels these input termin-als 28, 30. The predetermined potential which actuates the low impedance path means 44 is greater than the maxi-mum potential developed across the input terminals 28, 30 o the full-wave rectifier 26 when the lamp is operating so that once the arc strikes within the lamp 12, the low impedance path means 44 is rendered inoperative. As will be described hereinafter, the pulse generator 40 is actu-ated in time sequence just prior to the low impedance path means 44 so that once the arc is struck between the lamp electrodes 16, the low impedance path means 44 is there-after rendered inoperative.
An HID lamp keep-alive means 46 is operable from the AC energizing source and has output terminals 48, 50 which connect across the output terminals 32, 34 of the full-wave rectifier means 26 and the keep-alive means 46 serves to maintain the operation of the HID lamp during periods of conduction minima of the full-wave rectifier means 26. In other devices for operating such a light source, a large electrolytic capacitor is normally con-nected across the output terminals of the full-wave recti-fier in order to supply current during periods of conduc~
tion minima of the full-wave rectifier. Because of the current inrushes to the capacitor, the overall power factor of the device is impaired.

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6 49,224 The specific circuit as show~ in detail in Fig.
2 is designed to operate a 50 watt high pressure sodium arc discharge tube 52. The incandescent ballast filaments 18 are connected in parallel and each are rated at 150 watts, 120V AC, although different filament wattages could be substituted therefor to vary the light available from the unitary light source. The circuit input terminals 36, 38 are adapte~ to be connected across the household-type source of AC energizing potential and the lamp 52 is as previously described with respect to the arc enclosing envelope 14 and electrodes 16. As described, the incan-descent filament means 18 has two end portions 20 and 22.
The full-wave bridge rectifier means 26 com-prises the diode bridge Dl-D4 having two input terminals 28, 30 and two output terminals 32, 34. One end portion 20 of the filament ballast 18 connects to one input termi-nal 28 of the diode bridge 26 and the other end portion 22 of the filament ballast 18 connects to the input terminal 36 of the composite light source. The other input termi-nal 30 of the full-wave bridge 26 connects to the other input terminal 38 of the composite light source.
A hign-voltage lamp-starting pulse-generating means 40 is operable from the AC energizing potential and has an output terminal constituting a high-voltage elec-trode 42 terminating proximate the envelope 14 of the dis-charge device 52 in order to ionize the atmosphere therein through a field-effect mechanism. In this embodiment, a voltage boosting arrangement comprising transformer Tl, capacitors Cl, C2, diodes D5, D6 and dropping resistors Rl, R2 are used to boost the voltage available for the pulse generator 40. The pulse generator 40 is actuated th,ough diode D7 and voltage divider formed of resistors R3-R5 to charge capacitor C3. When the capacitor C3 charges to 40 volts, the diac Sl conducts, triggering the thyristor S2 which discharges the capacitors C4 and C5 causing pulse transformer T2 to generate a pulse of ap-proximately 4,000 volts which is applied to the field-, ~ . ' .: .~ ;
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7 49,224 effect electrode 42 to ionize the atmosphere within the arc tube envelope 14. The foregoing pulse generator will be triggered when a voltage of approximately 120 volts peak at the terminal 20 is sensed.
The low impedance path means 44 essentially connects in parallel with the pulse generator and com-prises a voltage divider formed of R6-R8, diac S3 and triac S4, along with capacitor C7. When the capacitor charges to a predetermined value, the diac S3 conducts, triggering the thyristor S4, which essentially places a short circuit across the input terminals 28, 30 of the full-wa~e rectifier 26. I~ the operation of the pulse generator 40 and low impedance path means 44 as shown in the embodiment of Fig. 2, the pulse generator is adapted lS to be actuated just prior to the low impedance path means.
As a specific example, a typical setting of the device will cause the pulse generator to be actuated when the voltage sensed is 120 volts peak with the low impedance path means being actuated when the voltage sensed is 130 volts peak. If the arc is initiated within the discharge device 52, the voltage across the input terminals ~8, 30 of the full wave rectifier 26 will not rise to a value sufficient to energize the low-impedance path means 44.
Once the low impedance path means is actuated, this in effect will provide a short circuit across the input term-inals 28, 30 of the full-wave rectifier 26 and the ballast filaments 18 will be energized to full incandescence for the remainder of the half cycle.
As noted hereinbefore, devices which utilize a large capacitor in parallel with the output terminals of the full-wave rectifier 26 will inherently have a rela-tively poor power factor because of the current inrush to the capacitor. The present design dispenses with such a capacitor and it is necessary to provide a current source in order to maintain the operation of the lamp 14 during periods of conduction minima of the full-wave rectifier 26. This is achieved by providing capacitors C8, C9 and .

8 4g,224 diodes D8, D9 connected in voltage doubling arrangement in circuit with the device input terminals 36, 38, with the output thereof being connected through a current limiting resistor R9 to the more positive output terminal 32 of the full-wave rectifier 26.
Summarizing the operation of the foregoing embodiment as shown in Fig. 1, the device as first turned on can be selected to provide one of two levels of bright-ness i~ desired, depending upon which ballasting filament is placed in circuit. During the first half cycle of operation, the pulse generator applies the high voltage pulse to the field-effect starting electrode 42 on the outside of the discharge tube envelope 14, with the major power flow being via the full-wave rectifier bridge 26 thereafter. During non-conducting intervals of the recti-fier bridge, the lamp current is maintained at a minimum sustaining value from the keep-alive circuit 46. If power is interrupted momentarily after the lamp has reached its operating temperature, light will be provided entirely by the ballast filament means 18 which then will be connected directly across the power line via the action of the voltage-sensitive low-impedance means 44. Since the low-impedance means 44 and the pulse generator act in concert each half cycle of energizing potential, the electronics will repeatedly attempt to restart the hot discharge lamp. As the lamp cools and then restarts, the pulse generator and low impedance path means are auto-matically deactivated. Once the discharge within the lamp 52 is initiated, it in effect is placed in series with the ballast filament means 18. The ballast filament 18 will initially incandesce brightl~ because of the low voltage developed across the discharge lamp 52. As the lamp warms up and the voltage drop thereacross increases, the ballast filament 18 will become dimmer and dimmer as the light output from the discharge lamp increases.
Following is a component chart for the circuit diagram as shown in Fig. 2. It should be noted that this ~15~
9 49,224 circuit is designed to operate a 50 watt high pressure sodium lamp and to operate a smaller wattage lamp, the components would be scaled down considerably.

COMPONENT CHART
Item Identification Dl-D4, D8, D9 IN5408 D5, D6, D7 IN5399 Cl 4~F-250V
C2 4~F-450V
C3-C7 O.Ol~F
C8, C9 40~F-450V
Rl, R2 51 KQ
R3, R6, R8 12 KQ
R4, R7 50 KQ pot R9 5 KQ, 12W
` Tl 120:30 T2 4KV Trigger Coil Radio Shack 272-1146 Sl, S3 40V DIAC
S2, S4 T2800D

In Fig. 3 is shown a circuit diagram of a great-ly simplified arrangement wherein the pulse generator and low impedance path means are combined into one unit by means of a silicon bilateral voltage triggered switch.
Upon application of a voltage exceeding the switch break-over point, the voltage sensitive switch turns on through a negative resistance region to a low on-state voltage.
Conduction then continues until current is interrupted or drops below the required device holding current level.
Thus in this application, once each half cycle, the switch will conduct at a predetermined voltage and conduction .

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49,224 will continue until the current passes through a minimum value. Such a switch is sold under the trademark SIDAC by Teccor Electronics, Inc., Dallas, TeY~as.
The circuit as shown in Fig. 3 comprises the apparatus input terminals 36, 38 which are adapted to be connected to a household-type source of AC energizing po-tential, the HID lamp 54 which comprises the arc-enclosing envelope 14 having electrodes 16 sealed therethrough and operable to sustain a high-intensity-discharge therebe-tween. The incandescent ballast filament 18 a has two endportions 20 and 22. The full-wave rectifier means 26 has two input terminals 28, 3Q and two output terminals 32, 34. One end portion 20 of the filament ballast 18a con-nects to one input terminal 28 of the full-wave rectifier 26 and the other end portion 22 of the filament ballast and the other input terminal 30 of the full-wave rectifier connect across the light source input terminals 36, 38.
The low impedance path means as previously described is a "SIDAC" switch 56 and it is selected to conduct when the potential developed thereacross is 120 to 130 volts. The pulse generator is combined with the switch 56 and comprises the pulse transformer T3 and a capacitor C10. When the SIDAC switch conducts, the capac-itor Cl0 is discharged, generating a high voltage pulse each half cycle of energizing potential, which high volt-age pulse is applied to the field-effect electrode 42.
Whether the lamp starts or not, for the remainder of the half cycle the closed switch 56 will provide a very low impedance path which will cause the incandescent filament 18 to incandesce for the remainder of the half cycle when the switch again opens. To provide starting for the lamp, capacitors C11 and C12 with diodes Dl0, D11 and Dl2 are arranged in a voltage doubler arrangement with the output of the circuit connected to the more positive output terminal of the full wave rectifier bridge 26 through a current limiting impedance Rl0.

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11 49,22g To review the circuit operation, consider a nominal power line voltage (117V rms, 165V peak) a fully charged (330V DC) starting-aid and keep-alive current source output capacitor (C12), a cold discharge lamp (54) and the SIDAC 56 with a nominal breakover voltage of 130 volts. As the power line sinusoidal increases, capacitor C10 charges to be substantially e~ual in voltage to the power line voltage. When the line voltage exceeds 130V
(about 52 electrical), the switch 56 suddenly conducts heavily, with its terminal voltage dropping to about one volt, and remains in that state until the next current zero of the power line (128 electrical later). In so "shorting", the switch 56 does two things: (1) it connects the incandescent ballast filament directly across the power line for the beginning of "instant light"; ~2) it causes capacitor C10 to discharge its energy into the high voltage pulse transformer T3 with the ionization produced inside the discharge lamp being sufficient to cause cur-rent indicated as il to flow through the lamp from the auxiliary current source. Lamp current cannot yet flow from the full-wave rectifier bridge 26 because the bridge is still "shorted" by the closed switch 56. By suitably choosing the components in the auxiliary current source, the discharge tube will remain in conduction through the next power line minimum. At that minimum point, the switch 56 recovers, and the rectified power line current (i2) goes through the now-conducting discharge device during the next half cycle. After this lamp starting event, the role of the auxiliary current source is the same as for the embodiment of Fig. 2, namely, to supply "keep-alive" current (i3) to the discharge tube during power line minima. With the discharge lamp operating, the starter/low resistance path becomes ~uiescent because the voltage at the "discharge tube input" line does not rise high enough to cause the SIDAC switch to breakover and conduct.

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12 49,224 A more realistic situation for lamp starting corresponds to the capacitors Cll and C12 as shown in Fig.
2 being initially in a discharged state. The act of applying power to the combination light source will actu-ally initiate two simultaneous events: (1) a train ofstarting pulses and bursts of ballast filament current will occur every half cycle of the energizing source, and (2) there ~ill be a build-up of charge on the capacitors Cll and C12 which will require perhaps 10 power line cycles for full charging. During this time light comes only from the incandescent ballast filament 18 if the dis-charge lamp 54 is not in a ~ondition to be started by tha applied DC voltage. If the discharge lamp is started, both the lamp and the incandescent ballast filament will provide light.
As a possible alternative embodiment, the resis-tor R10 which provides a current limiting impedance for the auxiliary current source may take the form of a second incandescent filament to supplement the overall light output, if desired.
In the embodiment as shown, the charging path for capacitor C12 is via Cll, D10 and D3. The diode Dll prevents reverse voltages on Cll if the user first applies the power when the input terminal 36 is positive with respect to the input terminal 38. The charging path for capacitor Cll is via diode D12.
As a possible alternative embodiment for the circuits of Fig. 2 or Fig. 3, the high-voltage electrode 42 could be connected to the lamp lead-in proximate the uppermost electrode 16 with a small additional capacitor connected between the electrode 42 and the transformer T3 to block the DC from the pulse transformer T3. A small high-frequency choke in the same lead-in conductor to which the electrode 42 connects would be used to block the high-voltage starting pulse from the ~.C. source.

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Claims (4)

13 49,224 CLAIMS:

1. A unitary light source comprising an HID
lamp and the light-emitting starting and operating circuit therefor, said light source providing illumination during the warm-up period required for said HID lamp and also after short periods of power-interruption when said HID
lamp is hot and thus difficult to start, said light source having input terminals adapted to be connected to a house-hold-type source of AC energizing potential;
said HID lamp comprising an arc-enclosing enve-lope having spaced electrodes sealed therethrough and operable to sustain a high-intensity-discharge therebe-tween;
incandescent tungsten filament ballast means having two end portions;
full-wave rectifier means having two input terminals and two output terminals, one end portion of said filament ballast means connecting to one input ter-minal of said full-wave rectifier means, the other end portion of said filament ballast means and the other input terminal of said full-wave rectifier means connecting across said unitary light source input terminals, and said HID lamp electrodes connecting across said output terminals of said full-wave rectifier means;
low impedance path means and high-voltage pulse-generating means operable from said AC energizing poten-tial and connected in parallel with said input terminals of said full-wave rectifier means, when said HID lamp is 14 49,224 not operating said low impedance path means is responsive each half cycle of said AC energizing potential to a predetermined potential developed across said input ter-minals of said full-wave rectifier means to be actuated to provide a path of low electrical impedance which parallels said input terminals of said full-wave rectifier means, said predetermined potential which actuates said low impedance path means being greater than the maximum poten-tial developed across said input terminals of said full-wave rectifier means when said HID lamp is operating, said pulse-generating means having an output terminal consti-tuting a high-voltage electrode operatively associated with said HID lamp, and actuation of said low impedance path means triggering the operation of said pulse-generat-ing means to generate a high-voltage of sufficient magni-tude to ionize the atmosphere within said arc-enclosing envelope of said HID lamp; and HID lamp keep~alive and starting-aid means having an input connected in circuit with said light source input terminals and an output connected across said output terminals of said full-wave rectifier means, said keep-alive and starting-aid means upon initial energiza-tion of said light source operating to store DC energy of the same polarity as the output of said full-wave recti-fier means and of predetermined charge and magnitude sufficient to sustain a discharge in said HID lamp for a short period during the starting thereof and also during periods of conduction minima of said full-wave rectifier means.

2. The light source as specified in claim 1, wherein said low impedance path means and high-voltage pulse-generating means comprises a two-terminal voltage-sensitive switch connected across said input terminals of said full-wave rectifier means, a pulse transformer having a primary winding and a second winding, a capacitor and the primary winding of said pulse transformer connected across the terminals of said voltage-sensitive switch 49,224 means, and the secondary winding of said pulse transformer connects to said high-voltage electrode.

3. The light source as specified in claim 1, wherein said HID lamp keep-alive and starting-aid means comprises a voltage doubler connected in circuit with said light source input terminals, and the more positive output terminal of said voltage doubler connects through a current limiting impedance to the more positive output terminal of said full-wave rectifier means.

4. A unitary light source comprising an HID
lamp and the light-emitting starting and operating circuit therefor, said light source providing illumination during the warm-up period required for said HID lamp and also after short periods of power-interruption when said HID
lamp is hot and thus difficult to start, said light source having input terminals adapted to be connected to a house-hold-type source of AC energizing potential;
said HID lamp comprising an arc-enclosing envel-ope having spaced electrodes sealed therethrough and operable to sustain a high-intensity-discharge therebe-tween;
incandescent tungsten filament ballast means having two end portions;
full-wave rectifier means having two input terminals and two output terminals, one end portion of said filament ballast means connecting to one input ter-minal of said full-wave rectifier means, the other end portion of said filament ballast means and the other input terminal of said full-wave rectifier means connecting across said unitary light source input terminals, and said HID lamp electrodes connecting across said output termin-als of said full-wave rectifier means;
high-voltage lamp-starting pulse-generating means operable from said AC energizing potential and hav-ing an output terminal constituting a high-voltage elec-trode terminating proximate said HID lamp, said pulse-generating means responsive to application of said AC

16 49,224 energizing potential across said light source input termi-nals when said HID lamp is not operating to generate high-voltage pulses which are of sufficient magnitude to ionize the atmosphere within said arc-enclosing envelope of said HID lamp, and after said HID lamp is operating said pulse-generating means is responsive to a lamp-operating parameter to be rendered inoperative;
low impedance path means connected in parallel with said input terminals of said full-wave rectifier means, when said HID lamp is not operating said low imped-ance path means is responsive each half cycle of said AC
energizing potential to a predetermined potential devel-oped across said input terminals of said full-wave recti-fier means to provide a path of low electrical impedance which parallels said input terminals of said full-wave rectifier means, said predetermined potential which actu-ates said low impedance path means being greater than the maximum potential developed across said input terminals of said full-wave rectifier means when said HID lamp is operating; and HID lamp keep-alive means having an output connected across said output terminals of said full-wave rectifier means and operable to supply operating energy to said HID lamp to maintain the operation thereof during periods of conduction minima of said full-wave rectifier means.