CIRCUIT FOR STARTING AND OPERATING DISCHARGE LAMPS

Abstract: Solid state circuit for a discharge lamp which is highly reliable and efficient in operation, and which is compact, lightweight and inexpensive to produce. This object is attained by eliminating inductive transformers, choke coils and all other inductive elements from the circuit. A full wave diode rectifier (D1-D4) has input terminals to an ac power source, and output terminals to the lamp. A current limiting capacitor (C1) is connected between the current source and one of the input terminals of the rectifier. A filter capacitor (C2) is connected across the output terminals of the rectifier. Voltage multiplying capacitance in the form of doubler type circuits (C3, C4, C5, C6 & C7) is connected across the output of the rectifier to increase the voltage for starting the lamp. A resistor (R1) is connected in series with the lamp to smooth the voltage peaks during operation of the circuit. The circuit primarily provides dc to the lamp, however, a small amount of ac is provided to the lamp to extend the life and prevent polarization of the lamp.

Description: Description * CIRCUIT FOR STARTING _ND OPERATING DISCHARGE LAMPS Technical Field The invention relates to systems for starting and operating gas discharge lamps, and more particularly, to circuits which ar -compact, lightweight, and inexpensive and highly efficient to start: and operate gas discharge lamps. A fluorescent lamp is an electric discharge light source. It consists of a phosphor coated glass tube having a cathode sealed in each end. A small quantity of inert gas mixture and a small amount of mercury are also sealed within the tube. When the mercury is ionized by an electric potential, ultraviolet radiation is produced which causes the phosphor coated walls to fluoresce,- generating diffused light. Fluorescent lamps have an electrical characteristic referred to as "negative resistance". That is, a given high voltage is required to start the lamp, and once started, a lessor voltage is required to sustain its operation. Backgroun Art The early prior art utilized large inductive trans¬ formers as ballasts to operate the lamps. The inductive ballasts have several inherent disadvantages. One such disadvantage is that the transformers are heavy and relatively expensive components. The inductors are also inefficient, with significant applied power being lost in the form of heat. In some cases, the filiment windings are only used to facilitate starting, however power is continuously applied to the elements as long as the lamp is operated, thus producing an additional heat loss. • Recent prior art circuits have been improved by the use of rectifiers as shown in U.S. Pat. No. 4,260,932 issued to Johnson. The circuit also utilizes a voltage doubler to increase the starting voltage to the lamp. However, all configurations of the circuit disclose an inductive transformer or a choke coil or other form of inductance. The choke coils and•inductance elements have the disadvantages previously discussed. The Johnson patent also shows a separate starter for the circuit. Another example of prior art is shown in U.S. Pat. No. 4,045,708 issued to " Neal. The Neal patent discloses inductively coupled coils utilizing tandum diode rectifiers to operate a discharge lamp. The circuit also shows the use of voltage doubler and quadrupler capacitor circuits along with the transformer to start the lamp. Nearly every known, circuit heretofore utilizes at least one choke coil or other inductance means to start or operate the lamp. Such systems are inherently heavy, costly and inefficient. Prior art systems also required a switching device to periodically reverse the polarity of the systems to prevent polarization of -the. lamps and migration of the phosphors. No system heretofore have disclosed a circuit consisting of only solid state diodes and capacitance to efficiently and inexpensively start and operate a discharge lamp. Disclosure of Invention In accordance with the present invention, the circuit includes a full wave rectifier having input terminals to a conventional alternating current * source, and output terminals to the lamp. A current limiting capacitor is connected between the current source and one of the input terminals of the rectifier. A filter capacitor is connected across the output terminals of the rectifier to limit the current during phase shifting to deliver a constant output. Voltage multiplying capacitance, in the form of doubler type circuits, is disposed across the output of the rectifier to increase the voltage for starting the lamp. A resistor is connected in series O P with the lamp which is operative after the lamp has started to eliminate any voltage peaks in the circuit, which -may be created by the capacitors, during normal operation of the lamp. The configuration and amount of the required voltage multiplying capacitance can be connected depending upon the input current source and the characteristics of the lamp. The circuit primarily provides direct current to the lamp, however, a small amount of alternating current is also provided by the circuit. The alternating current is sufficient to extend the life of the lamp and prevent polarization and migration of the phosphors within the lamp. The circuit is inexpensive and highly efficient. Brief Description of Drawings The details of the invention will be described in connection with the accompanying drawing, in which: FIG. 1 is a circuit diagram for starting and operating a discharge lamp in accordance with the present invention; FIG. 2 is a circuit diagram of a modification of the circuit shown in FIG. 1; and FIG. 3 is a circuit diagram of another embodiment of a discharge lamp in accordance with the present invention. Best Mode for Carrying Out the Invention Referring first to FIG. 1, there is shown a typical arrangement of the circuit of the present invention. A full wave rectifier means is shown as a full wave diode rectifier formed by diodes Dl, D2, D3 and D4 and has a set of input terminals 1 and 2 to an alternating current source, and a set of output terminals 3 and 4 to the lamp. Input terminal 1 includes a current limiting capacitor Cl between the rectifier input and the current source, which controls ' the current to that required to operate the lamp. A filter capacitor C2 is connected across the output. terminals 3 and 4. The filter capacitor operates, during phase shifting created by other elements, to limit the current and to maintain, a stable and constant output from the rectifier. The starting voltage requires a very high instantaneous voltage to initiate the arc of the lamp. This high voltage can be efficiently accomplished by using voltage multiplying capacitors and diodes arranged in doubler type circuits, which are well known. Capacitors C3.and C4 along with directional diodes. D5 and D6 form such a first doubler.circuit. The capacitors are connected in series with each other and in parallel across the output of the rectifier at connections 5 and 5. The junction 7 of capacitors C3 and C4 is connected at " connection 0 to the input 1 of the rectifier. The first doubler circuit creates a shift in phase and increases the no—load voltage by a factor * of . Assuming an input voltage of 118 vac (rms) ' , the no-load output voltage at connection 5 and 6 would be about ( 118 x 2\β ) 334 volts. For some systems, this 334 volt no-load output may be suff- icient to initiate the arc and start the lamp. In such systems this would complete the voltage multiplying circuit and the output would be connected to the lamp (as the configuration similarly shown in FIG.. 3) , After the arc is initiated, the load immediately drops to the operating voltage of the system, and the major portion of the lamp current derives from the full wave rectifier action of Dl, D2, D3 and D4. A unique feature of this circuit arrangement, is that a small amount of alternating current is also supplied to the lamp by the non-rectified junction 7 of the doubler circuit. The small ac supplied is sufficient to extend the life of the * lamp and prevent polarization and migration of the phosphores within the lamp. A resistor Rl is connected in series with the lamp to eliminate, or a least minimize, any voltage spikes created by the voltage doubling capacitors. In other systems, a higher voltage may be required to initate the arc to ignite the lamp. Another embodiment of " the present ' invention can include the addition of a. second doubler creating, a quadrupler circuit. Additional capacitors C5 and C6 along with directional diodes D7 and D8 form such a quadrupler circuit. The capacitors are connected in series with each other and in parallel across the output of the rectifier at connections 8 and 9. The junction 10 of the capacitors C5 and C6 is connected at 11 to the input terminal 2 of the rectifier. The voltage quadrupler circuit increases the input voltage by a factor of * . Assuming an input voltage of 118 vac (rms) , the no-load output voltage at connections 8 and 9 would be about ( 118 x ) 668 volts. The foregoing voltage multiplying circuit along with Rl may be suff¬ icient to start and operate many lamp systems and would therefore complete the circuit. In this circuit the small amount of ac voltage is supplied by the non- rectified junction 10 of the last doubler circuit. Other systems may require even higher starting voltages and .another embodiment of the invention can include an additional voltage multiplying circuit to complete the circuit as shown in FIG. 1. The addition of capacitor C7 connected at 12 to the output 3 of the rectifier, and connected at 0 to the input terminal 1 of the rectifier, along with diode D9, would multiply the input voltage by a factor of . Assuming an input voltage of 118 vac (rms) , the no-load output voltage at connection 9 and 12 would be about ( 118 x S^ ) 834 volts. This no-load voltage is sufficient to start most lamp systems and is the preferred embodiment of the invention. This circuit can also be used on lamps which may not require the maximum no-load output.- Although the no-load voltage is considered to build instantaneously, it increases through the stages of the capacitors so long as there is no load; once there is sufficient voltage to ignite the lamp, the lamp will ignite and the load will drop the voltage to the operating voltage of the system, therefore , ' the ' full wave rectifier with current limiting capacitance and five-times voltage multiplying capacitance means, can start and operate nearly every lamp system regardless of lamp size, and cover a wide range of lamp characteristics which may vary from the various suppliers of discharge lamps The values of the capacitors and the load resister will be designed to match the characteristics of the lamp system to obtain maximum efficiency of the system. As a typical example of the relative values of the components, for a 20 watt fluorescent lamp having an input voltage of 118 vac (rms) , the following values can be used: Cl = 10 jif C2 = 7 μf C3 = C4 = ' 1 μf C5 = C6 =.33 μf C7 =.01 μf Rl = 20 ohms After ignition of the lamp, the operating voltage of the circuit is about 68 volts (rms) at 400 milliamperes of current. About 7 volts is supplied to the lamp through connection 12 as alternating current to extend the life of the lamp as previously described. The remainder ' of the voltage is supplied as direct current by the rectifier. The foregoing example of the system components points out the relative size and associated cost of the elements comprising the circuit. The various elements of the circuit are shown as discrete components, however, the circuit could be readily combined into an integrated chip. A wide range of component values are possible, and various arrangements of components may be made by one skilled in the art without departing from the teachings of the present invention. ' Re erring now to FIG. 2, there is shown a circuit similar to that described in reference to FIG. 1 with a modification in the location of the current limiting capacitor. A current limiting capacitor CIO is placed between the alternating current source and the 0 connection of the rectifier input terminal 1, in series with capacitors C3 and C4. Whereas in Fig. 1, the current limiting capacitor-Cl i-s. shown between connection 0 and rectifier * terminal 1, in parallel with capacitors C3 and C4. The current limiting capacitor * location of CIO tends to smooth the voltage and decreases the peak value of the voltage multiplying circuits of the system. The circuit otherwise performs in a similar manner as described in reference to Fig. 1. The configuration of the current limiting capacitor in FIG- 2 forms the additional embodiments with the voltage doubler, the voltage quadrupler, and the five-tiraes voltage multiplying- circuit as described in reference to FIG. 1. - Referring now to FIG. 3, there is shown a system similar to the first doubler circuit described in reference to FIG. 1. The system is described separately because it is particularly utilized with an input ac source of 220 volts. A full wave rectifier is formed by diodes Dll, ' D12, D13 and D14 and has a ' set of input terminals 12 and 13 to the current source, and a set of output terminals 14 and 15 to the lamp. Input terminal 12 includes a current limiting capacitor Cll between the rectifier and the current source, which controls the current to that level required to operate the ' lamp. A filter capacitor C12 is connected across the output of the rectifier to maintain a constant output from the rectifier. The starting voltage with a 220 volt input may require only a first doubler circuit to initiate the arc to ignite the lamp. Capacitors C13 and C14 and diodes D15 and D16 form the doubler circuit. With an input of 220 vac (rms) , the no-load output at connections 16 and 17 would be about ( 220 x ) 633 volts. This should be sufficient to ignite most lamp systems, however, if additional starting voltage is required or desired, the voltage multiplying circuits can be added as described in reference to FIG. 1. The current limiting capacitor Cll may alternatively be located • between connection 19 and the current source as described in reference to FIG. 2. A resistor R2 is connected in series with the lamp to•eliminate any voltage spikes in the ^ operating * circuit. The foregoing embodiments have described a solid state circuit for starting and operating a discharge lamp which is highly reliable and efficient in operation. The circuit does not require a current reversing switch, or a separate starter system, or inductance elements of any type for operation. The circuit is compact, light¬ weight and inexpensive to produce.

Claims: Claims 1. A circuit for starting and operating a discharge lamp utilizing a source of alternating current, comprising: ' a full wave rectifier means connected between a set of input terminals to the alternating current source and a set of output terminals to the lamp; current limiting capacitance means disposed between the source of alternating current source and an input terminal of said rectifier; filter capacitance means disposed across the output terminals of said rectifier means, to facilitate a constant and stable output; voltage multiplying capacitance means disposed across the output of said rectifier means for increasing the starting voltage applied thereto; resistance means disposed in series with the lamp to minimize any voltage peaks during the operation of the lamp. 2. The circuit as defined in claim 1, wherein said voltage multiplying capacitance means comprises a voltage doubler circuit. 3. The circuit as defined in claim 1, wherein said voltage multiplying capacitance means- comprises a voltage quadrupler circuit. 4. The circuit as defined in claim 1, wherein said voltage multiplying capacitance means comprises a five-times voltage multiplier circuit. 5. The circuit as defined in claim 2, wherein said voltage doubler comprises: a third and fourth capacitance means connected in series with each other and disposed in parallel across the output of said rectifer means, with the junction of said third and fourth capacitance means connected to the input terminal of said rectifier means which includes the current limiting capacitance means; and a first pair of oppositely poled diodes connected in series between the corresponding output terminal of said recti ier means and said third and fourth capacitance means. 6. The circuit as defined in claim 5 which acts as a voltage quadrupler and which further comprises: a fifth and sixth capacitance means in series with each other and disposed in parallel across the output of said rectifier means,, with the junction of said fifth and sixth capacitance means connected to the ■ input terminal, which does not include the current limiting capacitance means, of said rectifier means;and a second pair of oppositely poled diodes, each connected in series between the corresponding output terminal of said rectifier means and said fifth and sixth capacitance means, to direct current flow. 7. The circuit as defined in claim 6 which acts as a five- times voltage multiplying circuit and which further comprises: * a seventh capacitance means connected in parallel -between an output terminal of said rectifier means and an input terminal of said rectifier means, and a fifth diode connected to the output of said rectifier means between the connection of said seventh capacitance means and the connection of said fifth capacitance means, to direct the flow of current. 8. The circuit as defined in claims 5,6 or 7 wherein said current limiting capacitance means is connected between the junction of said third and fourth capacitance means, and an input terminal of said rectifier means. The circuit as defined in claims 5, 6 or 7 wherein said current limiting capacitance means is connected between the source of alternating current, and the * junction of said third and fourth capacitance means.

Inventors: HAM BYUNG IL, VAKIL USMAN UMER, HAM, BYUNG, IL, VAKIL, USMAN, UMER
Applicants: LIGHTS OF AMERICA INC, LIGHTS OF AMERICA, INC.
Application year: 1981
Main classification: H05B37
IPC codes: H05B41