Circuit arrangement

Abstract: The invention relates to a circuit arrangement suitable for operating two fluorescent lamps (11, 12), comprising a ballast means (I) for providing power to said two fluorescent lamps to illuminate them, said ballast means providing power for preignition heating, for ignition and for post-ignition operation of said lamps, said ballast means being operable to attempt to ignite said lamps repeatedly should they fail to ignite. According to the invention, the circuit arrangement also comprises sensing means (I(11)) for causing said ballast means to cease trying to ignite said lamps after a predetermined time during which at least one of the fluorescent lamps has failed to ignite. This prevents flashing of one of the lamps for more than this predetermined time, if one of the lamps has deteriorated.

Description: The invention relates to a circuit arrangement suitable for operating two fluorescent lamps, comprising a ballast means for providing power to said two fluorescent lamps to illuminate them, said ballast means providing power for ignition and post-ignition operation of said lamps, said ballast means being operable to attempt to ignite said lamps repeatedly should they fail to ignite and sensing means for causing said ballast means to cease trying to ignite said lamps after a predetermined time during which at least one of the fluorescent lamps failed to ignite. Such circuit arrangements are known from European patent applications 0146683 and 111929. The invention aims to provide another such circuit arrangement. A circuit arrangement as described in the opening paragraph is therefore according to the invention characterized in that said ballast means provides power for pre-ignition heating and that said sensing means comprise a first capacitor and means for charging said first capacitor as a result of the voltage across one fluorescent lamp not being substantially equal to that across the other, said means for charging comprising two capacitors forming a bridge circuit with said two fluorescent lamps. Preferably said two fluorescent lamps can be connected in a circuit with said ballast means and said circuit arrangement includes restart circuit means responsive to the removal of one of said fluorescent lamps from said circuit and the insertion of a replacement fluorescent lamp into said circuit in place of said removed fluorescent lamp whereby said sensing means operates to allow said ballast means to attempt again to ignite said lamps. The restart circuitry preferably includes retry circuitry for responding to current flow through electrodes of said fluorescent lamps, said restart circuit means operating in response to said retry circuitry sensing the cessation of current flow through said lamps. Other objects, features and advantages of the invention will be apparent from the following description and appended claims when considered in conjunction with the accompanying drawing in which: figure 1 shows a ballast means connected to two fluorescent lamps with the addition of one version of the lamp life prediction circuit of this invention, and figure 2 shows a ballast means connected to two fluorescent lamps with an alternate version of the lamp life prediction circuit of this invention. In figure 1, I is a ballast means for providing power to fluorescent lamps 11 and 12 for preignition heating, for ignition and for post-ignition operation of said lamps. Ballast means I is operable to attempt to ignite said lamps repeatedly should they fail to ignite. Such a ballast means is for instance described in European Patent Application 0351012. The improvement discloses herein involves the provision of the prediction circuitry I(11). As shown in figure 1 prediction circuit (I)11 includes a resistor (I)R1 connected to a voltage source (I)V1 and to one electrode of lamp 12. That electrode of lamp 12 is also connected to ground through a resistor (I)R2. That same electrode of lamp 12 is connected directly to one of the electrodes of lamp 11 and to the other electrode of lamp 12 through capacitance (I)C1. The interconnected electrodes of lamps 11 and 12 are also connected to ground through capacitor (I)C2. The upper electrode of lamp 11 is connected through a capacitor (I)C3 to a junction point (I)J1. Junction point (I)J1 is connected through a capacitor (I)C4 to the lower electrode of lamp 12. Lamps 11 and 12 and capacitors (I)C3 and (I)C4 form a bridge through which capacitor (I)C5 may be charged under prescribed conditions to be described. Junction point (I)J1 is connected to ground through resistor (I)R3 and to capacitor (I)C5 through diode (I)D1 and resistor (I)R4. Capacitor (I)C5 is also connected to a second voltage source (I)V2 through diode (I)D2, which keeps capacitor (I)C5 from charging to a voltage higher than (I)V2. Capacitor (I)C5 is also connected to terminal K. Resistor (I)R5 is connected in parallel with capacitor (I)C5. The junction of diodes (I)D2 and (I)D3 is connected to the collector of transistor (I)T1 through resistor (I)R6. Terminal K is connected to ground through resistance (I)R7 and connected to a ballast means I. The emitter of transistor (I)T1 is connected to ground. Its base is connected through resistor (I)R8 to ground and also through resistor (I)R9 to the collector of transistor (I)T2. The collector of transistor (I)T2 is also connected to a voltage source (I)V3 through resistor (I)R10 and to terminal K through diode (I)D4. The emitter of transistor (I)T2 is grounded while its base is connected through resistors (I)R11 and (I)R12 to the circuit including the middle electrodes of lamps 11 and 12. The base of transistor (I)T2 is connected to ground through resistor (I)R13. The junction between resistors (I)R11 and (I)R12 is also connected to ground through capacitor (I)C6. As mentioned, capacitors (I)C3 and (I)C4 form a bridge circuit with lamps 11 and 12. The sizes of the capacitance of capacitors (I)C3 and (I)C4 are chosen to keep the bridge output voltage low during normal lamp operation. Thus, if lamps 11 and 12 have substantially the same operating characteristics, capacitors (I)C3 and (I)C4 should be equal so the bridge will be balanced and no significant voltage relative to ground will appear at junction point (I)J1 because the voltage across each lamp will be substantially equal to that across the other. If the performance of one of the lamps deteriorates so that it will not ignite, the bridge output voltage will remain high due mainly to the effect of capacitor (I)C1 which is connected across lamp 12. As a result, the voltage stored on capacitor (I)C5 will increase. After a predetermined time set by the values of resistor (I)R4 and capacitor (I)C5, the voltage on terminal K will reach a prescribed value. When this prescribed value is reached, the signal at terminal K stops the attempts of ballast means I to ignite the lamps. This can for instance be realized by rendering a switching element between the supply voltage source and the ballast means non-conducting as soon as the signal at terminal K reaches the prescribed value. Another possibility, in case the configuration of ballast means I is as described in European Patent Application 0351012, is to connect terminal K to line "V LAMP". If the voltage on line "V LAMP" reaches the prescribed value, above that of the voltage on line "V REG", the frequency control of the ballast means will cause line "START" to be grounded. As long as line "START" remains grounded, the system remains in its pre-ignition operation condition and will be prevented from trying to ignite lamps 11 and 12. In order to allow ignition to be repeated when a bad lamp is replaced by a good one, transistor (I)T2 is employed to sense the removal of the bad lamp. It does this when the trickle current provided by source (I)V1 through the center electrodes of lamps 11 and 12 ceases while the lamp is removed. This lack of trickle current causes transistor (I)T2 to turn-off which holds the voltage on terminal K high as well as turning transistor (I)T1 on to discharge capacitor (I)C5. Upon replacement of the bad lamp with a good one, transistor (I)T2 is once again turned on by the trickle current through the center electrodes of lamps 11 and 12. As a consequence of transistor (I)T2 being turned on, transistor (I)T1 is turned-off. As a result of capacitor (I)C5 being discharged the voltage at terminal K is no longer above the prescribed value thereby permitting the ballast means I to try to ignite lamps 11 and 12. Figure 2 shows a prediction circuit which functions in substantially the same manner as the prediction circuit in figure 1. The difference between the arrangement in figure 2 and that in figure 1 is that the current through the center electrodes of lamps 11 and 12 is sensed through a resistor (I)R14 and a small transformer (I)TR1. In addition, resistor (I)R12 shown in figure 1 is replaced by diode (I)D12 in figure 2. A comparison of figure 1 with figure 2 will show that like elements have been identified by the same reference characters in both figures. It should be apparent that various modifications of the above will be evident to those skilled in the art and that the arrangement described herein is for illustrative purposes and is not to be considered restrictive.

Claims: A circuit arrangement for operating two fluorescent lamps (11, 12), comprising a ballast means (I) for providing power to said two fluorescent lamps to illuminate them, said ballast means providing power for ignition and post-ignition operation of said lamps, said ballast means being operable to attempt to ignite said lamps repeatedly should they fail to ignite and sensing means ( (I)C2, (I)C3, (I)C4, (I)R3, (I)D1, (I)R4, (I)C5, (I)R5, (I)D2, (I)V2, (I)D3, K, (I)R7) for causing said ballast means to cease trying to ignite said lamps after a predetermined time during which at least one of the fluorescent lamps failed to ignite, characterized in that said ballast means provides power for pre-ignition heating and that said sensing means comprise a first capacitor ((I)C5) and means for charging said first capacitor as a result of the voltage across one fluorescent lamp not being substantially equal to that across the other, said means for charging comprising two capacitors ((I)C3, (I)C4) forming a bridge circuit with said two fluorescent lamps. A circuit arrangement as claimed in claim 1, wherein said two fluorescent lamps (11, 12) can be connected in a circuit with said ballast means (I) and said circuit arrangement includes restart circuit means ((I)R6, (I)T1, (I)R8, (I)R9, (I)D4, (I)T2, (I)R10, (I)V3, (I)R11, (I)R13, (I)C6, (I)R12) responsive to the removal of one of said fluorescent lamps from said circuit and the insertion of a replacement fluorescent lamp into said circuit in place of said removed fluorescent lamp whereby said sensing means operates to allow said ballast means to attempt again to ignite said lamps. A circuit arrangement as claimed in claim 2, wherein said restart circuit means includes retry circuitry ((I)R11, (I)R13, (I)C6, (I)R12) for responding to current flow through electrodes of said fluorescent lamps, said restart circuit means operating in response to said retry circuitry sensing the cessation of current flow through said lamps.

Inventors: MATTAS CHARLES B, MATTAS, CHARLES B.
Applicants: PHILIPS ELECTRONICS NV, PHILIPS ELECTRONICS N.V.
Application year: 1991
Main classification: H05B41
IPC codes: H05B41, H05B37