EP0673184B1 - Fluorescent lamp power supply and control circuit for wide range operation - Google Patents

Fluorescent lamp power supply and control circuit for wide range operation Download PDF

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Publication number
EP0673184B1
EP0673184B1 EP19950103762 EP95103762A EP0673184B1 EP 0673184 B1 EP0673184 B1 EP 0673184B1 EP 19950103762 EP19950103762 EP 19950103762 EP 95103762 A EP95103762 A EP 95103762A EP 0673184 B1 EP0673184 B1 EP 0673184B1
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EP
European Patent Office
Prior art keywords
circuit
current
fluorescent lamp
lamp
coupled
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EP19950103762
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German (de)
English (en)
French (fr)
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EP0673184A3 (en
EP0673184A2 (en
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James M. Williams
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Linear Technology LLC
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Linear Technology LLC
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    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B41/00—Circuit arrangements or apparatus for igniting or operating discharge lamps
    • H05B41/14—Circuit arrangements
    • H05B41/26—Circuit arrangements in which the lamp is fed by power derived from dc by means of a converter, e.g. by high-voltage dc
    • H05B41/28—Circuit arrangements in which the lamp is fed by power derived from dc by means of a converter, e.g. by high-voltage dc using static converters
    • H05B41/282—Circuit arrangements in which the lamp is fed by power derived from dc by means of a converter, e.g. by high-voltage dc using static converters with semiconductor devices
    • H05B41/2821—Circuit arrangements in which the lamp is fed by power derived from dc by means of a converter, e.g. by high-voltage dc using static converters with semiconductor devices by means of a single-switch converter or a parallel push-pull converter in the final stage
    • H05B41/2824—Circuit arrangements in which the lamp is fed by power derived from dc by means of a converter, e.g. by high-voltage dc using static converters with semiconductor devices by means of a single-switch converter or a parallel push-pull converter in the final stage using control circuits for the switching element
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B41/00—Circuit arrangements or apparatus for igniting or operating discharge lamps
    • H05B41/14—Circuit arrangements
    • H05B41/36—Controlling
    • H05B41/38—Controlling the intensity of light
    • H05B41/39—Controlling the intensity of light continuously
    • H05B41/392—Controlling the intensity of light continuously using semiconductor devices, e.g. thyristor
    • H05B41/3921—Controlling the intensity of light continuously using semiconductor devices, e.g. thyristor with possibility of light intensity variations
    • H05B41/3925—Controlling the intensity of light continuously using semiconductor devices, e.g. thyristor with possibility of light intensity variations by frequency variation

Definitions

  • This invention relates to fluorescent lamp power supplies. More particularly, this invention relates to a fluorescent lamp power supply and control circuit which enables the lamp to be regulated to shine at a substantially constant intensity as the lamp ages or the power supply voltage fluctuates, and which also enables lamp intensity to be adjusted continuously and smoothly over a chosen intensity range including, if desired, substantially from full OFF to full ON.
  • Fluorescent lamps are finding increased use in systems requiring an efficient and broad-area source of visible light.
  • portable computers such as lap-top and notebook computers use fluorescent lamps to back-light or side-light liquid crystal displays to improve the contrast or brightness of the display.
  • Fluorescent lamps have also been used to illuminate automobile dashboards, and are being considered for use with battery-driven backup emergency EXIT lighting systems in commercial buildings.
  • Fluorescent lamps find use in these and other low-voltage applications because they are more efficient, and emit light over a broader area, than incandescent lamps. Particularly in applications requiring long battery life, such as in the case of portable computers, the increased efficiency of fluorescent lamps translates into extended battery life or reduced battery weight, or both.
  • a power supply and control circuit In low-voltage applications such as those discussed above, a power supply and control circuit must be used to operate the fluorescent lamp. This is because power typically is provided by a 3-20 volt DC source, while fluorescent lamps generally require 100 volts AC or more to efficiently operate. Accordingly, a power supply and control circuit is needed to convert the available low DC voltage into the necessary high AC voltage.
  • a further disadvantage of some previous known fluorescent lamp power supply and control circuits is that lamp intensity may change as the lamp ages or as the power supply voltage fluctuates.
  • a further disadvantage of some known fluorescent lamp power supply and control circuits is that they can be a source of radio frequency emission. Such emission can cause undesirable electromagnetic interference with nearby devices, and can degrade overall circuit efficiency.
  • a power supply and control circuit and method for driving a fluorescent lamp from a low voltage D.C. source A regulator circuit, powered by the D.C. source, is coupled to a DC-to-AC inverter the output of which, in turn, is coupled to a first terminal of the lamp.
  • the inverter converts, under control of the regulator circuit, the low-voltage DC supplied by the input DC power source to high-voltage sinusoidal AC sufficient to operate the fluorescent lamp.
  • a second terminal of the lamp is coupled to a circuit which senses and produces a signal indicative of the magnitude of current conducted by the lamp.
  • This current sense signal is fed back to the regulator in such manner so as to regulate the current supplied to the lamp by the inverter.
  • the current conducted by the lamp -- and, hence, the intensity of the light emitted by the lamp -- are regulated as a function of the feedback signal.
  • the terminals of the fluorescent lamp may be coupled across the terminals of the transformer's AC output such that the lamp fully floats without any direct connection to the driving circuitry.
  • the output of the fluorescent lamp is indirectly regulated by circuitry which monitors the lamp's drive power. As a result, asymmetries in the lamp's drive are reduced to cause a more uniform distribution of energy and light output across the length of the lamp.
  • a means is a provided in both embodiments to enable the lamp's drive current to be varied by a user, thus allowing lamp intensity to be smoothly and continuously adjusted (without dead-spots or pop on) over a chosen range of intensities.
  • This range of intensity variation can include, if desired, from substantially full OFF to full ON.
  • the combination of a switching regulator and an inverter for producing substantially sinusoidal AC results in a highly efficient circuit which emits a minimum of spurious RF radiation.
  • floating the lamp without direct electrical connection to the driving circuitry and indirect monitoring of the feedback signal result in a more uniformly distributed electrical field, and enhances uniformity of the light emitted from the fluorescent lamp.
  • FIG. 1 is a block diagram of the fluorescent lamp power supply and control circuit of the present invention.
  • input DC power source 35 provides power for the circuit.
  • Power source 35 can be any source of DC power.
  • power source 35 can be a nickel-cadmium or nickel-hydride battery providing 3-5 volts.
  • power source 35 can be a 12-14 volt automobile battery and power supply.
  • fluorescent lamp 15 can be any type of fluorescent lamp.
  • fluorescent lamp 15 can be a cold- or hot-cathode fluorescent lamp.
  • Input DC power source 35 supplies low DC voltage to regulator circuit 25 (at terminal 27) and high-voltage inverter 20 (at terminal 21).
  • Regulator circuit 25 can be a linear or switching regulator but, for maximum efficiency, a switching regulator is preferred.
  • the output of regulator circuit 25 is taken from terminal 28.
  • Terminal 26 is a feedback terminal adapted to receive a feedback signal by which the output of regulator 25 can be controlled. If regulator 25 is a switching regulator, the feedback terminal causes the duty cycle of the regulator's switching transistor to be controlled to regulate the output.
  • High-voltage inverter 20 receives a low voltage DC input at terminal 21 from input DC power source 35, and produces at output terminal 23 an AC voltage sufficient in magnitude to drive fluorescent lamp 15.
  • the AC voltage produced by inverter circuit 20 is 100 volts or more.
  • Terminal 22 is a control terminal coupled to receive from terminal 28 of regulator circuit 25 a control signal.
  • the control signal regulates the output of high-voltage inverter 20, in a manner as described below.
  • the output of inverter 20 is coupled to lamp 15 at the lamp's terminal 16 (typically, through a conventional ballast capacitor not shown).
  • inverter circuit 20 preferably converts DC power to sinusoidal AC power.
  • circuit 30 functions to produce, at terminal 31, a feedback signal FB indicative of the magnitude of current I LAMP conducted by fluorescent lamp 15.
  • circuit 30 includes a current sense impedance coupled between terminal 32 and ground, with signal FB at terminal 31 being a voltage developed across that impedance which is proportional to the magnitude of I LAMP .
  • variable resistor 34 can be used to adjust the magnitude of feedback signal FB and, hence, the loop gain of the circuit. As a result, the intensity of fluorescent lamp 15 can be adjusted with control 34 smoothly and continuously (without dead-spots or pop-on) throughout a chosen range of intensities, including if desired, from substantially full OFF to full ON.
  • the circuit of FIG. 1 operates as follows.
  • High voltage inverter 20, in combination with regulator circuit 25, delivers high voltage AC power to fluorescent lamp 15.
  • the current through fluorescent lamp 15, I LAMP is sensed by current feedback circuit 30.
  • Circuit 30 produces a feedback signal FB proportional to the magnitude of I LAMP .
  • the output of regulator circuit 25 is modulated as a function of the magnitude of I LAMP .
  • the output of regulator circuit 25, controls and modulates the output of inverter 20.
  • the magnitude of current (I LAMP ) conducted by fluorescent lamp 15 -- and, hence, the intensity of light emitted by the lamp -- is regulated to a substantially constant value.
  • Circuit 10 functions to keep the lamp current I LAMP substantially constant, independent of lamp impedance or power supply voltage. Thus, as a lamp's impedance goes up or down as the lamp ages, circuit 10 adjusts to such change as appropriate so as to maintain a regulated constant current and lamp intensity, even though the lamp ages. Circuit 10 similarly adjusts as the power supply voltage fluctuates.
  • variable resistor 34 The operating current of lamp 15 (and, hence, the intensity of the lamp) can be adjustably controlled by adjusting the feedback gain via variable resistor 34.
  • the magnitude of feedback signal FB applied to regulator 25 is varied. This causes lamp current I LAMP to vary responsively. Because fluorescent lamps have high impedance and are essentially current-driven devices, varying the magnitude of I LAMP results in variation of the lamp 15's intensity. Because it is lamp current that is being directly controlled, variable resistor 34 produces a smooth and continuous adjustment of lamp intensity throughout a chosen range of intensity adjustment, including if desired, from full OFF to full ON, without dead-spots or pop-on.
  • variable resistor 34 is shown for purposes of illustration, and not limitation. Other circuit techniques and configurations could as well be used to provide variable control of the lamp current. For example, similar lamp intensity control action could as well be obtained by adding a signal (not shown) at the feedback point (terminal 26 of regulator circuit 25) to adjust loop gain.
  • FIG. 2 is a schematic diagram of one exemplary embodiment of the fluorescent lamp power supply and control circuit of FIG. 1.
  • input DC power source 35 supplies power for fluorescent lamp power supply and control circuit 100.
  • Input DC power source 35 which can be any conventional power source, is used to supply low DC voltage (approximately 3-20 volts) to push-pull high-voltage inverter circuit 120 and current-mode switching regulator circuit 125.
  • Switching regulator 125 can be any of a number of commercially available switching regulators. In the exemplary embodiment of FIG. 2, however, regulator 125 preferably is an LT-1072 integrated circuit switching regulator (available from Linear Technology Corporation of Milpitas, California).
  • regulator circuit 125 When implemented using a LT-1072 switching regulator, regulator circuit 125 includes pin V IN (terminal 127) coupled to power source 35, terminals E1, E2 and GND coupled to ground, frequency compensating terminal V C coupled through capacitor 162 to ground, switched output pin V SW (terminal 128) and feedback pin V FB (terminal 126).
  • Inverter circuit 120 is a current-driven high-voltage push-pull inverter which converts the DC power from input DC power source 35 to high-voltage, sinusoidal AC. Inverter 120 is a self-oscillating circuit. Transistors 122 and 123 conduct out of phase and switch each time transformer 121 saturates. During a complete cycle, the magnetic flux density in the core of transformer 121 varies between a saturation value in one direction and a saturation value in the opposite direction. During the cycle time when the magnetic flux density varies from negative minimum to positive maximum, one of transistors 122 and 123 is ON. During the rest of the cycle time (i.e., when the magnetic flux density varies from positive maximum to negative minimum), the other transistor is ON.
  • Switching of transistors 122 and 123 is initiated when the magnetic flux density in transformer 121 begins to saturate. At that point in time, the inductance of transformer 121 decreases rapidly toward zero, with the result that a quickly rising high collector current flows in the transistor which is ON. This current spike is picked up by transformer bias winding 121b of transformer 121. Because the base terminals of transistors 122 and 123 are coupled to bias winding 121b of transformer 121, the current spike is fed back into the base of the transistor which produced it. As a result, that transistor drops out of saturation and into cutoff, and the transistor is turned OFF. Accordingly, the current in transformer 121 abruptly drops and the transformer winding voltages then reverse polarity resulting in the turning ON of the other transistor which previously had been OFF. The switching operation is then repeated for this second transistor.
  • Transistors 122 and 123 alternately switch ON and OFF at a duty cycle of approximately 50 percent.
  • Capacitor 124 coupled between the collectors of transistors 122 and 123, causes what would otherwise be square-wave-like voltage oscillation at the collectors of transistors 122 and 123 to be substantially sinusoidal. Capacitor 124, therefore, operates to reduce RF emissions from the circuit.
  • the frequency of oscillation is primarily set by the combination of the characteristics of transformer 121, capacitor 124 coupled between the collectors of transistors 122 and 123, fluorescent lamp 15, and ballast capacitor 160 coupled to secondary winding 121d of transformer 121.
  • Capacitor 156 reduces the high frequency impedance so that transformer center tap 121a sees zero impedance at all frequencies.
  • Transformer 121 steps-up the sinusoidal voltage at the collectors of transistors 122 and 123 to produce, at secondary winding 121d, an AC waveform of sufficiently high voltage to drive fluorescent lamp 15 (shown coupled to secondary winding 121d through ballast capacitor 160).
  • Ballast capacitor 160 inserts a controlled impedance in series with lamp 15 to minimize sensitivity of the circuit to lamp characteristics and to minimize exposure of fluorescent lamp 15 to DC components.
  • Inverter 120 in conjunction with current-mode switching regulator circuit 125, thus operates to deliver a controlled AC current at high voltage to terminal 16 of fluorescent lamp 15.
  • Inductor 143 coupled between terminal 128 of regulator 125 and the emitters of transistors 122 and 123, is an energy storage element for switching regulator 125.
  • Inductor 143 also sets the magnitude of the collector currents of transistors 122 and 123 and, hence, the energy through primary winding 121c of transformer 121 that is delivered to lamp 15 via secondary winding 121d.
  • Schottky diode 142 coupled between input DC power source 35 and switched output pin V SW , maintains current flow through inductor 143 during the off cycles of switching regulator circuit 125.
  • Resistor 157 DC biases the respective bases of transistors 122 and 123.
  • the current delivered to lamp 15 by transformer 121 is regulated to a substantially constant value by a feedback loop including lamp 15, diode 144 and feedback circuit 130.
  • Diode 144 in conjunction with diode 143, half-wave rectifies lamp current I LAMP .
  • Diode 143 shunts negative portions of each cycle of I LAMP to ground, and diode 144 passes positive portions of that current (representing one-half the lamp current I LAMP ) to feedback circuit 130.
  • Feedback circuit 130 comprises resistor 151 and capacitor 152 coupled in series between the cathode of diode 144 and ground. This produces a voltage, proportional to the magnitude of I LAMP , across capacitor 152. This voltage (FB) is presented to the feedback pin (terminal 126) of switching regulator 125. The above connections close the feedback control loop which regulates lamp current. Resistors 146 and 147, connected in parallel with resistor 151 and capacitor 152, allow for DC adjustment in the voltage (FB) which is presented to the feedback pin.
  • the voltage (FB) on feedback pin 126 of switching regulator circuit 125 is generally below the internal reference voltage of regulator circuit 125 (i.e., 1.23 volts for the LT-1072 discussed above).
  • full duty cycle modulation at the switched output pin V SW (terminal 128) of regulator circuit 125 occurs.
  • inductor 143 conducts current which flows from center tap 121a of transformer 121, through transistors 122 and 123, into inductor 143. This current is deposited in switched fashion to ground by the regulator's action.
  • This switching action controls lamp 15's average current I LAMP , the amount of which is set by the magnitude of the feedback signal FB at the feedback terminal V FB (terminal 126).
  • variable resistor 147 The feedback loop forces switching regulator 125 to modulate the output of inverter 120 to whatever value is required to maintain a constant current in lamp 15.
  • the magnitude of that constant current can, however, be varied by variable resistor 147. Because the intensity of lamp 15 is directly related to the magnitude of the current through the lamp, variable resistor 147 thus allows the intensity of lamp 15 to be adjusted smoothly and continuously over a chosen range of intensities, including full OFF to full ON without "dead-spots" or "pop-on” at low lamp intensity.
  • the circuit of FIG. 2 can be implemented using commercially available components.
  • the circuit can be constructed and operated using the components and values set forth in Table 1, below: Regulator 125 LT1072 (available from Linear Technology Corporation of Milpitas, California) Transformer 121 SUMIDA-6345-020 (available from SUMIDA ELECTRIC (USA) CO., LTD., of Arlington Heights, Illinois) or COILTRONICS CTX110092-1 (available from Coiltronics Incorporated, of Pompano Beach, Florida)
  • Inductor 143 300 microhenrys(COILTRONICS CTX300-4)
  • Capacitor 124 low loss 0.02 microfarad Metalized polycarb WIMA- FKP2 (Germany) preferred
  • Capacitor 152 1 microfarad Capacitor 156 10 microfarads Capacitor 160 33 picof
  • the circuit With an input DC power source voltage of approximately 4.5 to 20 volts, the circuit operates at an efficiency of approximately 78 percent with approximately 1400 volts peak-to-peak appearing across the secondary of the transformer. When operating with an input DC power source voltage of approximately 3 to 5 volts, the efficiency increases to approximately 82 percent.
  • the circuit of FIG. 2 could be modified in numerous ways without departing from the spirit and scope of the invention.
  • the intensity of lamp 15 could be varied other than by variable resistor 147 by variably introducing a signal S into the feedback loop as shown in FIG. 3.
  • Signal S operates to vary the loop gain of the feedback loop by varying the magnitude of feedback signal FB applied to regulator 125.
  • the introduction of signal S in FIG. 3 enables the intensity of lamp 15, to be varied without "dead-spots" or "pop-on.”
  • signal S in FIG. 3 could be taken from the output of a conventional photocell or other optical detector circuit (not shown) which monitors the intensity of ambient light.
  • a conventional photocell or other optical detector circuit (not shown) which monitors the intensity of ambient light.
  • Such a circuit would enable the fluorescent lamp power supply and control circuit to compensate and adjust the fluorescent lamp intensity in response to the intensity of ambient light within the environment.
  • the fluorescent lamp's intensity could be regulated to a high value.
  • the fluorescent lamp's intensity could be regulated to a low value.
  • signal S could come from virtually any other circuit to cause the intensity of the fluorescent lamp to vary in some desired manner.
  • FIGS. 4A-4C show various exemplary circuit configurations for driving a plurality of fluorescent lamps.
  • two fluorescent lamps 15A and 15B are driven in series between ballast capacitor 160 and terminal 17.
  • Feedback circuit 130 is coupled in a fashion similar to that shown in FIG. 3 so as to sample lamp current I LAMP and provide current regulation.
  • ballast capacitors 160A and 160B are shown in FIG. 4B coupled commonly to secondary winding 121d, they could also be coupled to separate windings on the secondary side of transformer 121.
  • transformer 121 could include a plurality of secondary windings with each lamp respectively coupled to the different windings through its respective ballast capacitor.
  • ballast capacitors 160A and 160B are shown in FIG. 4C coupled commonly to secondary winding 121d, they could also be coupled to separate windings on the secondary side of transformer 121.
  • transformer 121 could include a plurality of secondary windings with each lamp respectively coupled to the different windings through its respective ballast capacitor.
  • FIGS. 5A-5D show various exemplary configurations of another embodiment in accordance with a further aspect of the invention in which a fluorescent lamp's output is indirectly monitored and in which the lamp may be floated across the terminals of an output transformer.
  • FIGS. 5A-5D are simplified diagrams of circuits to provide regulation of a fluorescent lamp over an extended range of intensities, such that the lamp's intensity is more consistently distributed along the longtitudal length of the lamp.
  • the circuits shown in FIGS. 5A-5D are particularly effective for operating cold cathode fluorescent lamps, the circuits of FIGS. 5A-5D may also be used to drive hot cathode flourescent lamps (i.e., the hot cathode filaments are driven as if they were cold cathode electrodes).
  • a DC-AC converter 248 drives the primary coil of transformer 121.
  • Converter 248 is a simplified representation of various components shown in FIG. 1, and includes at least high voltage inverter 20 and regulator 25.
  • the terminals of the secondary coil of transformer 121 are coupled across a cold cathode fluorescent lamp 15.
  • a conventional ballast capacitor 160 is also shown coupled in series with the lamp 15.
  • Regulation of lamp 15 is provided by supplying a feedback signal to converter 248.
  • the feedback signal developed across an impedance 210 (shown as a resistor, although other suitable forms of impedance may be used), is proportional to the input current.
  • the feedback signal is coupled to converter 248 to regulate lamp 15 and, hence, the amount of light emitted by the lamp 15.
  • This feedback signal which indirectly monitors the lamp's drive power, differs from the arrangement shown in FIGS. 1-4 in which a feedback signal is extracted directly from the lamp output circuitry.
  • impedance 210 is preferably a variable impedance which receives user inputs that cause converter 248 to vary the intensity of lamp 15 correspondingly.
  • Floating lamp 15 across the secondary output of transformer 121 to isolate the lamp from its drive circuitry, and indirectly measuring the drive provided to the lamp, is advantageous because no connection is involved which would cause asymmetrical drive to the lamp 15. This results in a more uniformly distributed electric field within the lamp, which enhances the lamp's ability to uniformly emit light along its entire length at lower operating currents.
  • An additional benefit is that a lower amplitude waveform out of transformer 121 may be used to operate the lamp.
  • FIG. 5B shows another way to monitor indirectly the input power and, hence, the drive current of lamp 15.
  • transformer 121 is the same as transformer 121 of FIG. 5A, except that is provided with an additional winding 256 on the primary side.
  • Winding 256 senses the magnetic flux induced in the transformer 121, and responsively generates a signal proportional to that flux. This signal indirectly monitors the drive to the lamp, because it is indicative of the energy transferred to the lamp.
  • Additional winding 256 may be wound simultaneously during the winding of transformer 121 (as a trifilar winding) to provide a more precise measurement of the flux of the primary, or it may be separately wound. In either event, the signal generated by winding 256 is coupled to converter 248, as shown in FIG.
  • FIG. 5C shows yet another way to indirectly monitor the drive to lamp 215.
  • the current passing through the return (ground) terminal of converter 248 is monitored via impedance 215 (shown as a resistor, although other suitable forms of impedance could be used) coupled in series between converter 248 and ground.
  • the voltage developed across impedance 215 is used as a feedback signal, and coupled as shown to a feedback terminal of converter 248 to control the lamp's drive as hereinbefore described.
  • impedance 215 shown as a resistor, although other suitable forms of impedance could be used
  • the voltage developed across impedance 215 is used as a feedback signal, and coupled as shown to a feedback terminal of converter 248 to control the lamp's drive as hereinbefore described.
  • One disadvantage of the approach of FIG. 5C, as compared to that of FIG. 5A, is that additional signal processing within or around converter 248 may be required to obtain good regulation as operating conditions change. This is so because the return line of converter 248 typically contains highly non-linear signal components
  • FIG. 5D shows still another way to monitor indirectly the drive provided to lamp 15.
  • feedback signal FB is generated by sampling a portion of transformer 121's primary AC voltage signal.
  • the feedback loop includes capacitor 220, one terminal of which is coupled to a terminal of the primary winding of transformer 121.
  • the other terminal of capacitor 220 is coupled to the anode of diode 225 and to a first terminal of impedance 230.
  • the other terminal of impedance 230 is coupled to ground, while the cathode of diode 225 is coupled to the feedback input terminal of converter 248.
  • FIGS. 5A-5D are intended only to be representative, but not exhaustive, of such circuits. It should also be apparent to persons skilled in the art that indirect measurement of the drive to the lamp does not require floating the lamp from the drive circuitry, and that indirect measurement may be accomplished even where the windings of the transformer are directly coupled. For example, any of the indirect measurement techniques shown in FIGS. 5A-5D can be applied to any of the lamp configurations shown in FIGS. 2, 3 and 4A-4C (where the transformer secondary winding is coupled to a common ground).
  • FIG. 6 shows an exemplary circuit employing the principles of the circuit of FIG. 5A. More particularly, FIG. 6 shows circuitry of FIGS. 2 and 3, but modified in accordance with the principles discussed with respect to FIG. 5A so that lamp 15 is symmetrically driven to enhance the uniformity of the light emitted along the length of the lamp's tube.
  • the circuit of FIG. 6 includes inverter 120 and current mode switching regulator 125.
  • Inverter 120 in conjunction with regulator 125, operates to deliver a controlled AC current at high voltage to terminal 16 of fluorescent lamp 15.
  • the coupling of lamp 15 to the secondary winding 121d is changed so that lamp 15 is floated across the winding.
  • This arrangement causes the drive to lamp 15 to be symmetrical, thus causing its light output along the length of the lamp's tube to be more uniformly distributed as heretofore discussed.
  • FIG. 6 Also changed in FIG. 6 is the circuitry to sense and regulate the flow of current in the tube. In FIG. 6, this sensing is done indirectly (i.e., without direct electrical connection to the loop including the lamp) in order to avoid introducing undesirable asymmetry into the lamp's drive.
  • An additional change in FIG. 6 is that the DC bias for transistor 122 (within inverter 120) is set by resistor 274 which is coupled to the base of transistor 122.
  • the circuitry to regulate the current to lamp 15 comprises current sensing circuit 270.
  • Circuit 270 provides a feedback signal to regulator 125 (at V FB ) that is proportional to the input current I INPUT of inverter circuit 120 as follows.
  • Input DC power source 35 applies power to the negative input of operational amplifier 273 through resistor 278, and to the positive input through shunt resistor 280.
  • Amplifier 273 generates a voltage signal that is proportional to the current sensed across shunt resistor 280 (the input current to inverter 120). This voltage signal is coupled to the base of FET switch 272 of feedback circuit 285.
  • the output signal causes FET switch 272 to saturate, thereby creating a low resistance conductive path across the switch such that the drain voltage of switch 272 represents an amplified, single-ended version of the shunt voltage.
  • Resistors 278, 279, and 280 of feedback circuit 285 are chosen to ensure that FET switch 272 fully saturates.
  • Feedback circuit 285 includes resistors 278 and 286 coupled in series with switch 272. Capacitor 287 and resistor 288 are coupled from resistor 286 to ground, with the capacitor 287 being coupled to the terminal of resistor 286 that is coupled to the feedback terminal of switching regulator 125. Feedback circuit 285 produces a voltage that is proportional to the magnitude of I INPUT , in the form of the shunt voltage, across capacitor 287. This voltage is presented as feedback signal FB to the feedback pin (terminal 126) of switching regulator 125 to close the feedback control loop which regulates lamp current. Resistor 288 allows for DC adjustment in the voltage (FB) presented to the feedback pin.
  • the current sensing circuit 270 of FIG. 6 can be implemented using commercially available components. Exemplary components are set forth in Table 2, below: OperationalAmplifier 273 LT-307A (available from Linear Technology Corporation of Milpitas, California) N-Channel FETSwitch 272 TP0610 (available from Siliconix of Santa Clara, California) Resistor 274 1 kohm Resistor 278 499 ohms Resistor 279 100 kohms Resistor 280 0.3 ohm Resistor 286 10 kohms Resistor 288 4.99 kohm Capacitor 287 10 microfarads
  • FIG. 7 illustrates another exemplary circuit employing the principles of the circuit of FIG. 5D.
  • FIG. 7 shows circuitry of FIGS. 2 and 3 modified in accordance with the principles discussed with respect to FIG. 5D, so that lamp 15 is symmetrically driven to enhance the uniformity of the light emitted along the length of the lamp's tube.
  • the circuit of FIG. 7 includes inverter 120 and regulator 125.
  • Inverter 120 in conjunction with regulator 125, operates to deliver a controlled AC current at high voltage to terminal 16 of fluorescent lamp 15.
  • the coupling of lamp 15 to the secondary winding 121d is changed so that lamp 15 is coupled across the winding.
  • this arrangement causes the drive to lamp 15 to be symmetrical, its light to be more uniformly distributed.
  • Circuit 260 monitors the AC voltage across the primary winding of transformer 121 and provides a feedback signal voltage that is proportional to input current (I INPUT ) to the inverter circuit 120.
  • the current sensing circuit 260 includes capacitor 261, which couples the AC signal from the primary winding of transformer 121 to the resistor 262 and the anode of diode 263. Diode 263 half-wave rectifies the AC output signal of transformer 121.
  • Resistor 264 and variable resistor 265 produce a voltage across capacitor 266 that is proportional to the input current of inverter 120. This voltage is coupled as signal FB to the feedback pin of regulator 125.
  • Variable resistor 265 allows for DC adjustment in the signal voltage (FB), so that a user can vary the intensity of lamp 15.
  • the current sensing circuit 260 of FIG. 7 can also be implemented using commercially available components.
  • the circuit can be constructed and operated using the following components and values: Resistor 262 10 kohms Resistor 264 20 kohms Resistor 265 18 kohms Capacitor 261 .01 microfarads Capacitor 266 1 microfarad Diode 263 1N4148
  • FIGS. 8A and 8B show a plurality of fluorescent lamps being driven symmetrically.
  • two fluorescent lamps 15A and 15B are driven in series between ballast capacitor 160 and terminal 17.
  • Feedback circuit 260 is coupled in a fashion similar to that shown in FIG. 7 so as to sample the current passing through the primary winding of the transformer and provide indirect current regulation of lamps 15A and 15B.
  • a feedback signal is generated that is proportional to the current input to the inverter.
  • ballast capacitors 160A and 160B are shown in FIG. 7B coupled commonly to secondary winding 121d, they could also be coupled to separate windings on the secondary side of transformer 121.
  • transformer 121 could include a plurality of secondary windings with each lamp respectively coupled to the different windings through its respective ballast capacitor.

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EP19950103762 1994-03-16 1995-03-15 Fluorescent lamp power supply and control circuit for wide range operation Expired - Lifetime EP0673184B1 (en)

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US21386594A 1994-03-16 1994-03-16
US213865 1994-03-16

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EP0673184A2 EP0673184A2 (en) 1995-09-20
EP0673184A3 EP0673184A3 (en) 1996-08-28
EP0673184B1 true EP0673184B1 (en) 2004-10-27

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Family Applications (1)

Application Number Title Priority Date Filing Date
EP19950103762 Expired - Lifetime EP0673184B1 (en) 1994-03-16 1995-03-15 Fluorescent lamp power supply and control circuit for wide range operation

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EP (1) EP0673184B1 (ja)
JP (1) JPH0855691A (ja)
DE (1) DE69533681D1 (ja)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2008106745A1 (en) * 2007-03-08 2008-09-12 Cp Envirotech Pty Ltd Improved lighting apparatus

Families Citing this family (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE59812414D1 (de) 1997-04-24 2005-01-27 Siemens Ag Schaltungsanordnung zum dimmbaren betrieb einer leuchtstofflampe
DE19733939A1 (de) * 1997-08-06 1999-02-11 Mannesmann Vdo Ag Schaltungsanordnung zum dimmbaren Betrieb einer Leuchtstofflampe
US6107751A (en) * 1998-12-01 2000-08-22 Billings; Keith Current fed, parallel resonant ballast
DE10254983A1 (de) * 2002-11-26 2004-06-03 Robert Bosch Gmbh Elektrische Schaltung zur Ansteuerung von mehreren Entladungsröhren
CN102448235B (zh) * 2010-10-13 2013-12-11 硕颉科技股份有限公司 萤光灯管的驱动装置与方法
ITBO20120672A1 (it) * 2012-12-17 2014-06-18 Schneider Electric Ind Italia S P A Circuito oscillatore di alimentazione per sorgenti di illuminazione ed altri utilizzatori elettrici equivalenti

Family Cites Families (2)

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Publication number Priority date Publication date Assignee Title
US4920302A (en) * 1987-01-27 1990-04-24 Zenith Electronics Corporation Fluorescent lamp power supply
US5001386B1 (en) * 1989-12-22 1996-10-15 Lutron Electronics Co Circuit for dimming gas discharge lamps without introducing striations

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2008106745A1 (en) * 2007-03-08 2008-09-12 Cp Envirotech Pty Ltd Improved lighting apparatus

Also Published As

Publication number Publication date
EP0673184A3 (en) 1996-08-28
JPH0855691A (ja) 1996-02-27
EP0673184A2 (en) 1995-09-20
DE69533681D1 (de) 2004-12-02

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