Electronic quad ballast with improved hot restart

Abstract

 A unique ballast circuit arrangement for a low pressure discharge lamp provides an improved electrode preheat circuit which insures the same proper preheat start each time the lamp is turned on, including hot restart conditions. Electronic circuitry converts a low frequency AC input to a high frequency AC output, which is provided to the low pressure discharge lamp. A preheat circuit having a positive temperature coefficient element, a bidirectional switch, and a capacitor connected in series with both lamp electrodes, provides proper start conditions under all start conditions. Cathode quiescent losses during normal lamp operation are eliminated, thereby simultaneously improving ballast efficiency and system efficacy values of the ballast circuit arrangement and the low pressure discharge lamp.

Description

Technical Field

[0001] The present invention relates generically to all fluorescent lamps that are prone to improper instant starting under typical operating conditions and, more particularly, to compact fluorescent lamps (CFL) which are ballasted electronically at high frequency to insure a proper starting scenario under all start conditions, particularly a hot restart condition.

Background Art

[0002] In the field of residential and/or consumer lighting, there have been significant efforts made in the past several years to encourage more widespread public use of compact fluorescent lamps in place of less efficient incandescent lamps. Because of the significant energy savings that a fluorescent lamp offers over the use of an incandescent lamp while still attaining a comparable level of light output, public acceptance of such a lamp could contribute to the overall aim of conserving energy and the natural resources that are used to generate such energy. To this end, compact fluorescent lamps have been introduced and are the fastest growing segment in the fluorescent lamps marketplace today.

[0003] Lamps that use mercury along with an inert gas, such as Argon, as a means of converting ultraviolet energy into visible light are classified as low pressure fluorescent discharge lamps. One such family of compact lamps that are commercially available are called twin tube lamps and typically range in wattage from 5W to 50W. Double twin tube lamp types, generically called quads, are also commercially available, operate within the same range of wattage, and also have the desirable compactness feature. Additionally, this invention also can apply to any fluorescent lamp, regardless of size or voltage, that is prone to improper instant start conditions, and particularly to hot restart conditions.

[0004] Since many of the electronic ballasts developed for these compact lamps develop high starting voltages, many of the compact lamps, including quad and hex types, can all be prone to an improper instant start condition. Two examples of prior art circuits which attempt to alleviate the starting problems associated with electronically ballasted compact fluorescent lamps can be found in U.S. Patent Nos. 4,647,817 and 4,647,820 issued respectively to Fahnrich et al and Chermin et al. Although each patent discusses the use of a PTC element as a means for preheating the electrodes of the lamp, there is no discussion of the circuits operation under a hot restrike condition. Another example of a ballast circuit for a compact fluorescent lamp can be found in U.S. Patent No. 5,122,712 issued to Hirschmann. In this patent, a PTC element is used in combination with a diode so as to insure the cut-out of the starter circuit after initialization thereby eliminating energy loss through the PTC. Yet another example of an electronic ballast for a compact fluorescent lamp which exhibits preheat capabilities can be found in U.S. Patent No. 5,027,033 issued to Zuchtriegel. In this patent a relay contact is disposed in the PTC circuit for cutting out operation of the preheat circuit. A rectifier and capacitor circuit is used to control the relay coil and as such suffers in terms of the cost and complexity associated with the overall ballast configuration described in this patent.

[0005] It is therefore highly desirable and an object of the present invention to provide an improved electronic ballast having special circuitry to insure proper starting under all conditions, including hot restart conditions.

Summary of the Invention

[0006] The present invention provides a ballast circuit arrangement particularly suited for application with a compact fluorescent type discharge lamp. The ballast arrangement has been developed to provide a voltage sensitive, bi-directional electronic switch added in series with a positive temperature coefficient (PTC) element. The ballast arrangement of the present invention may be used with any fluorescent lamp that is prone to improper instant starting, and is particularly applicable to compact fluorescent lamps, including quad and hex type fluorescent lamps that are electronically ballasted. Since many of the electronic ballasts for compact fluorescent lamps develop high starting voltages, such lamps can be prone to an improper instant start condition and can therefore benefit from the ballast circuit of the present invention.

[0007] In accordance with one embodiment of the present invention, a ballast circuit arrangement for a discharge lamp comprises a PTC element for initially providing a low resistance path for proper electrode heating. A bidirectional switching means is connected in series with the PTC element for improving hot restart conditions by insuring that this low resistance path is properly connected electrically for each time the lamp power is switched on. Finally, a series connected capacitor is provided to properly set the value of the electrode preheat current.

[0008] Accordingly, it is an object of the present invention to provide a ballast circuit which will improve the hot restart characteristic of discharge lamps such that the hot restart condition is as satisfactory as the normal, i.e., cold, start condition. It is also an inherent advantage of the present invention that such a ballast circuit will improve ballast efficiency and efficacy of the system, because it eliminates the losses associated with the quiescent cathode current during normal operation. The ballast circuitry of the present invention also can improve overall lamp life because of the improved restart condition.

[0009] Other objects and advantages of the invention will be apparent from the following description, the accompanying drawings and the appended claims.

Brief Description of the Drawings

[0010] In the following detailed description, reference will be made to the attached drawings in which:

Fig. 1 is a typical schematic representation of an electronic ballast circuit for a compact fluorescent lamp constructed in accordance with the prior art;

Fig. 2 is an overview in block diagram form of an electronic ballast circuit constructed in accordance with the present invention;

Fig. 3 is a schematic representation of the electronic ballast circuit of Fig. 2, in accordance with the present invention.

Detailed Description of the Preferred Embodiments

[0011] Referring to the drawings, in Fig. 1 there is illustrated a prior art schematic representation of an electronic ballast circuit 10 used with an existing integral ballasted compact fluorescent lamp (CFL) 12. Input voltage/current wave shapes are electrically connected to a full wave bridge rectifier 14 which converts a low frequency, on the order of 60 Hertz, input to a rectified DC. The circuit may further include an electrical fuse 16 and a transient protection device, such as a metal oxide varistor 18, at the input. Various electrical filters consisting of capacitors 20 and 22, resistors 24 and 26, and inductor 28 smooth out the DC current so that a more stable DC current can be applied to a high frequency inverter circuit 30 that transforms the DC to high frequency AC. The capacitor 22 and the resistors 24 and 26 comprise an RC time constant network for a start inverter circuit of the electronic ballast circuit 10. A first switch, such as a SIDAC switch 27, provides an input to the start inverter circuit 30.

[0012] Continuing with Fig. 1, the high frequency AC current then passes through ballasting impedances, including a feedback transformer 32 and a resonant ballast inductor 34, which set the proper starting/operating values to be applied to the lamp 12. The circuit further includes capacitors 36 and a parallel resonant capacitor 38. A preheat electrode circuit 40, includes a PTC element 42 and a series capacitor 44.

[0013] Referring now to Fig. 2, there is illustrated a block diagram representation of a typical electronic ballast circuit constructed in accordance with the present invention. An input 46, having a fuse and transient protection, electrically connects AC voltage/current wave shapes to an AC/DC bridge rectifier 48, which has a DC output. Inverter 50 transforms the DC to high frequency AC which passes through high frequency ballasting impedances at block 52. The high frequency ballasting impedances from block 52 set the proper electrode preheating value at block 54 and the proper operating value for the lamp at block 56. The electrode preheating step of block 54 contains a bidirectional, voltage sensitive, electrical switch means, such as a SIDAC, discussed in more detail with reference to Fig. 3.

[0014] Referring now to Fig. 3, there is illustrated a schematic representation of the circuit block diagram of Fig. 2. Electronic ballast circuit 58 of Fig. 3 may be used with any existing integral ballasted compact fluorescent lamp (CFL) 12, to insure a proper starting scenario under all start conditions, particularly hot restart conditions. As in Fig. 1, input voltage/current wave shapes are electrically connected to the full wave bridge rectifier 14 which converts a low frequency input to a rectified DC. Electrical filters smooth out the DC current so that a more stable DC current can be applied to the high frequency inverter circuit 30 that transforms the DC to high frequency AC. This high frequency AC current then passes through ballasting impedances which set the proper starting/operating values to be applied to the lamp 12.

[0015] Continuing with Fig. 3, it is seen that circuit 58 is uniquely different from the prior art circuit 10 of Fig. 1, in that a bidirectional electronic switching means 60 has been added to a preheat electrode circuit 62, which now comprises the switch 60, a PTC element 64, and a series capacitor 66. The PTC element 64 is electrically connected in series with the bidirectional switch 60 for initially providing a low resistance path for proper electrode preheating. The series connected capacitor 66 properly sets the electrode preheat current for the electrodes of the lamp 12. The electrodes are situated inside the glass of the lamp, one at each end, to supply electrons to supply current for operating the lamp 12. In a preferred embodiment of the invention, the switch 60 is a bidirectional, voltage sensitive, electrical switch, such as a SIDAC switch. A SIDAC switch will reduce the sputtering of the emission mix on the electrodes during hot restart, by insuring that the electrodes are properly preheated, even for a hot restart condition.

[0016] Continuing with Fig. 3, the bidirectional switch 60 is closed when the input power to the ballast is off. The instant the power is turned on, current flows through the preheat electrode circuit 62, and the lamp 12 then subsequently starts. Once the lamp is started, the bidirectional switch 60, which is voltage sensitive, electrically opens, thus stopping any quiescent current flow through the PTC 64 of the electrode preheating circuit 62. Elimination of the quiescent current permits the PTC 64 to return to its low electrical value so that the next time the power is turned on, either normally or with a hot restart, the preheating electrode circuit 62 works perfectly.

[0017] The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that modifications and variations can be effected within the spirit and scope of the invention.

Claims

1. A ballast circuit arrangement for a low pressure discharge lamp effective for controlling current to operate the lamp, the ballast circuit arrangement comprising:
   electronic circuitry for converting a low frequency AC input to a high frequency AC output to the low pressure discharge lamp; and
   a preheat circuit connected across electrode members associated with the discharge lamp, the preheat circuit having bidirectional switching means for providing proper electrode preheat conditions to the electrodes for any start condition.

2. A ballast circuit arrangement as claimed in claim 1 wherein the preheat circuit comprises:
   a positive temperature coefficient element connected in series with the bidirectional switching means for initially providing a low resistance path for proper electrode preheating; and
   a series connected capacitor for properly setting the electrode preheat current for the electrodes.

3. A ballast circuit arrangement as claimed in claim 2 wherein the bidirectional switching means provides for simultaneous improvement of ballast efficiency and efficacy values by eliminating quiescent electrode losses during normal lamp operation.

4. A ballast circuit arrangement as claimed in claim 2 wherein the bidirectional switching means provides for proper electrode preheat conditions to the electrodes during a hot restart condition.

Drawing