FR2520963A1 - CATHOD HEATING CIRCUIT FOR FLUORESCENT LAMPS - Google Patents

Abstract

THE INVENTION CONCERNS CIRCUITS ASSOCIATED WITH FLUORESCENT LAMPS. A CIRCUIT INTENDED TO START AND OPERATE TWO FLUORESCENT LAMPS 11, 12 CONNECTED IN SERIES INCLUDES IN PARTICULAR A CATHODE 21 HEATING TRANSFORMER WHICH INCLUDES A SECONDARY WINDING 36 A CENTRAL TAP 37 CONNECTED TO THE CATHODES WHICH ARE RESPECTIVE OF 14, 16 SIDE OF THE CONNECTION BETWEEN THE TWO LAMPS. THIS CIRCUIT EXTENDS THE LIFETIME OF THE CATHODES BY PREVENTING A MOVEMENT OF THE "HOT SPOTS" EMITTING ELECTRONS ON THE CATHODES, WHEN THE HEATING CURRENT IS CUT AFTER LAMPS PRIMING. APPLICATION TO LIGHTING.

Description

The present invention relates to the field of

  for initiating and operating reciprocating gas-fed lamps connected in series, such as fluorescent lamps, having cathodes which are initially heated by an alternating heating current to facilitate priming; heating

  being then cut off during normal operation.

  In fluorescent lamps of this type, the discharges into the gas occur because of the emission of electrons from the cathodes, in each lamp The electrons are not emitted by the entire cathode, but by a small " "hot spot" of each cathode, the hot spots initially located at the end of each cathode at which the supply voltage of the

  lamp is applied, and these hot spots are moving

  gressively along the cathodes away from the extremes

  in which the supply voltage is applied, during the life of the lamp, as the

  the emission material located in the hotspots

improve with use.

  The alternating emission of electrons by each cathode of each lamp ionizes the gas in the lamp, which creates ions that flow to the other cathode of the lamp and bombard the cathode, creating alternating hot spots in the lamps. lamp cathodes during each half-cycle of the AC supply voltage Because of the thermal inertia of the cathodes, these points remain hot so as to facilitate the emission of electrons from

  of these points during each subsequent half-cycle of the

  alternatively, in which the polarity of the

the lamp is reversed.

  U.S. Patents 4,009,412 and 4,010,339 describe

  fluorescent lamps connected in series, with cir-

  fired which apply a supply voltage across the lamps connected in series, and which also initially apply a heating current to the cathodes, to heat them up to the electron emission temperature, after which these circuits cut off the current during the normal operation of the lamps, and after the cathode hot spots have been established, the temperature of these hot spots being sufficient to provide appropriate electron emission during normal lamp operation. cathodes saves several watts of electrical energy that would otherwise be consumed if the lamp cathodes were continually heated with the heating current during normal lamp operation A basic principle of the invention is based on the determination that in such lamp systems, the service life of lamps is reduced by the fact that accelerated deterioration of

cathodes of the lamps.

  It is an object of the invention to provide an improved reciprocating circuit and system for starting and operating a series of series connected gas discharge lamps, such as fluorescent lamps, in which the cathodes of the lamps are initially heated.

  by an alternating heating current applied to these

  , and in which the heating current is suppressed or cut off during normal lamp operation An essential purpose is to increase the useful life of lamps

  by extending the service life of their cathodes.

  Briefly and according to a preferred embodiment, the invention consists of a circuit for initiating and operating a set of series-connected gas discharge lamps, such as fluorescent lamps, in which an alternating cathode heating current is initially applied to the cathodes of the lamps to facilitate their initiation, after which this current is cut off during the normal operation of the lamps The invention improves and increases the useful life of the lamps, by the use of a power supply circuit. lamps that cause cathode heating currents to be cut off, cathode "hot spots", which emit electrons, remain on the cathodes at the locations they were in before the heating currents were shut down. cathode one accomplishes this by employing a

  transformer winding with central grip and connec-

  both the central grip at one end of each catheter

  at the connection point of the series-connected lamps, and connecting the respective ends of this coil to the remaining ends of these cathodes The center-tap winding may be in the form of two windings whose ends are connected together

  to form an equivalent center-fit winding.

  The rest of the description refers to the drawings

  annexed which respectively represent: Figure 1: a diagram of a combination of lamps

  fluorescents connected in series, in accordance with the prior art.

  with a supply voltage applied across the lamps and with cathode heating currents applied to the cathodes, this diagram showing an example of the electron flow direction in each lamp between a hot spot on a cathode and a hot spot sure

the other cathode.

  Figure 2: a diagram identical to that of the figure

  re 1, except that the cathode heating currents have been cut off for normal lamp operation, and that the position of the hot spot has changed (which

  is not desirable) on one of the cathodes.

  Figure 3: a diagram, according to a mode of realization

  preferred embodiment of the invention, of a combination of series-connected fluorescent lamps, with a supply voltage applied across their terminals and cathode heating currents applied to the cathodes, this diagram showing by way of example a flow direction of the electrons in each lamp between a hot spot on a cathode and a

hot point on the other cathode.

  FIG. 4: a diagram identical to that of FIG. 3, except that the cathode heating currents have been cut off for normal operation, this diagram showing that the positions of the hot spots on the

  cathodes remain the same as in Figure 3.

  In FIG. 1, a pair of elongated fluorescent lamps 11, 12 are electrically connected in series, as will be described. The lamp 11 has a pair of cathodes 13, 14 located respectively near the ends of this lamp and the lamp 12 has a pair

  cathodes 16, 17, located respectively close to the ends

  lamps, in a classic way Each of the catho-

  can be conventionally a wound tungsten wire, coated with a material that easily emits electrons when it is sufficiently hot At the point of connection between the lamps 11, 12, the cathodes 14, 16 are connected together in parallel, from an electrical point of view, with the "a" ends of the cathodes connected together and the

  ends "b" of the cathodes connected together.

  The circuit includes a source of electrical energy

  alternative 18 which provides a lamp supply voltage of an appropriate value, such as a few hundred volts, which can be supplied across an output winding 19, and which can be a so-called high frequency, from about 20 kHz to 100 kHz, although the invention

  is not limited to a particular frequency range.

  The end "a" of the winding 19 is connected to the end

  the "b" end of the coil 19 is connected to the "b" end of the lamp cathode 17 A cathode heating transformer 21 has a primary winding 22 connected to the terminals of all or part of the output winding 19, as for example between the points "b" and "c" of the latter, via a switch 23 which can be of any suitable type, including those described in the above-mentioned patents.

  cathode comprises a secondary winding 26 which is connected

  at the terminals of the lamp cathode 13, a secondary winding

  27 which is connected jointly across the

  lamps 14 and 16, and a secondary winding 28 which

  connected to the terminals of the lamp cathode 17, the

  of these secondary windings suitable for heating

  cathodes at electron emission temperatures.

  When the switch 23 is closed, as shown in FIG. 1, the voltage and the current of

  heating are applied to the cathodes The heating voltage

  cathode age and the supply voltage of the lamps

  winding 19 alternate at the same frequency

  convenience, Figure 1 shows the voltage polarities

  half-cycles during which the polarity of the

  supply voltage of the lamps is positive at the end "a" of the cathode 13, and negative at the end "b" of the cathode

  17, and in which the "a" ends of all

  have a positive polarity and the ends "b" of the

  Cathodes have a negative polarity During the other half

  voltage cycles, all these polarities are reversed Pen-

  in that the power supply voltage from the winding 19 is of positive polarity on the cathode 13 and of negative polarity on the cathode 17, and the fact that the polarities of individual cathode are those shown, the electrons circulate in the lamp 11 from the end "b" of the cathode 14, of negative polarity, and the electrons circulate in the lamp 12 from the end "b" of the cathode 17, of negative polarity In the lamp 11, the electrons coming from the end "b" of the cathode 14 cause the ionization of the gas contained in the lamp and the ions of the gas circulate towards the cathode 14 and bombard it at its end "b" (or near this end "), which heats up a small region and creates a" hot spot ", this electron movement from the cathode 14 is indicated by an arrow 31 In a similar fashion , in the lamp 12,

  the electrons that come from the "b" end of the catheter

  of 17 cause ionization of the gas in the lamp, and

  gas ions flow to cathode 17 and bombard the

  ci at its end "b", which warms a region and creates a hot spot; this movement of electrons from the cathode

  17 is indicated by an arrow 32 During the following half-cycle

  with alternative voltages, all polarities

  1 are inverted, and the electrons cir-

  from hot spots at the extreme

  mites "a" cathodes 13 and 16, and the gas ions flow to the ends "a" cathodes 13, 16, which creates

  hot spots on these electrodes Due to the thermal inertia

  cathodes, they remain sufficiently hot during

  alternating half-cycles to be able to emit easily

  after these hot spots have been established.

  blues, the cathode heating currents are no longer

  necessary and can be cut off The circulation of electricity

  trons and ions in lamps, indicated generically

  by the arrows 31 and 32, creates discharges in the gas lamps, which generates ultraviolet radiation under

  the effect of which phosphor coatings on

  the lamps create visible light in a way

well known.

  When the cathode heater control switch 23 is opened, to interrupt the cathode heating currents, as shown in FIG. 2, the hot spot of one of the cathodes 14, 16 moves towards the other end of this cathode, as indicated by the new position of the arrow 32 ', for which the hot spot of the cathode 16 has moved towards the end "b" of this cathode This is due to the fact that the current search for the path with the lowest impedance This displacement of the hot spot to a part of the cathode which is not heated, or whose heating has decreased due to the breaking of the cathode heating current,

  J causes a deterioration of the emitting material of

  cathode trons, due to the extraction by the electric field, or "spraying" of the electron-emitting material on the cathode, which reduces the useful life of the lamp This displacement of the hot spot is due to the parallel connections of the cathodes and the cathode heating coil 27 The displacement of the hot spot occurs on the cathode 14 or 16, depending on the one whose hot spot is the hottest; the hottest point

hot tends to stay in place.

  Figures 3 and 4 show a way of realizing

  preferred embodiment of the invention and these figures are respectively

  1 and 2, with the exception that the interconnection and the cathode heating circuits for the cathodes 14 and 16 located at the point of connection between the lamps 11, 12 connected to each other. series, have been changed to prevent movement of the

  cathode hot spot at the time of the interruption of

cathode heating rents.

  In Fig. 3, the cathodes 14 and 16 at the point of connection between the lamps 11 and 12 are heated by a center-engaged secondary winding, 36, which is set on the cathode heating transformer 21; the central plug 37 is connected together with the end "b" of the cathode 14 and at the end "a" of the cathode 16, and the ends of the winding 36 are respectively

  connected to the end "a" of the cathode 14 and to the end

  cathode "b" 16 This interconnection and cir-

  baked cathode heating establish an electrical connection

  direct contrast between the end "b" of the cathode 14 and the end "a" of the cathode 16 In contrast to Figure 1 wherein the ends of the cathodes 14 and 16 having the same heating voltage polarities are connected together, in Figure 3 one end of each cathode is connected to one end of the other cathode so that these ends have voltage polarities of

  The direction of circulation of electri-

  trons 31, 32 in the lamps are the same as on the

figure 1.

  As shown in FIG. 4, when the cathode heater switch 23 is opened to interrupt

  heating by the cathode current, the circuit paths

  the electrons, 31, 32, in the lamps remain unchanged and the hot spots which have been established at the "b" end of the cathode 14 and at the "a" end of the cathode 16 remain in place and do not move, as is the case in the circuit of the prior art of Figures 1 and 2 Thus, the invention extends the life of the lamps, preventing the displacement of hot spots of the cathodes when the heating current cathode is cut, this displacement producing, as explained above,

  extraction or "spraying" of the emitting material

  this electrons from the cathode, during the establishment

  of the new displaced hot spot.

  this improvement through the use of a new

  connection of the cathodes and a new cathode heating circuit which includes a direct electrical connection

  between the ends of the cathodes located at the point of con-

  between the lamps, these extremities being the seat of the formation of electron-emitting hot spots when

  The heating current is applied to the cathodes.

  As above, the electron flow arrows 31 and 32 represent the electron flow direction from or near hot spots at the "a" ends of cathodes 13 and 16. , while

  the half-cycles of the lamp supply voltage (pro-

  coming from the energy source 18) during which the winding

  output 19 gives a positive polarity on the catheter

  13 During the remaining half cycles of the lamp supply voltage, the polarity is reversed, the directions of the arrows 31 and 32 are reversed and the hot spots emit electrons are at the ends "b" of the cathodes 14 and 17 Each of these hot spots can

  a virtually constant electron emission temperature

  during lamp operation, because of the frequency

  quence of alternative power supply.

2520963-

Claims (3)

  1 Circuit designed to initiate and operate   a set of series-connected gas discharge lamps (11, 12), each lamp having a pair of cathodes (13, 14; 16, 17) and each cathode having a pair of terminals (a, b) for receiving a cathode heating current, characterized in that it comprises   means (18, 19) for applying an alternating voltage   power supply to the terminals of the lamps connected in series, and means (21) for applying a current   alternative to cathode heating lamps and includes   transformer winding (36) with central   the, means connecting the central plug (37) of the winding to a terminal (a, b) of each of the cathodes (14, 16) which are at the point of connection between the lamps (11, 12) connected to series, and means respectively connecting the ends of the center-engaging winding (36) to the remaining terminals (b, a) of the   cathodes mentioned last (14, 16).   Circuit according to Claim 1, characterized in that it comprises means (23) for cutting the heating current of the cathodes (13, 14; 16, 17) after   that discharges into the gas corresponding to the functioning   have been established in lamps (11, 12).   3 Circuit according to claim 2, characterized in that it comprises means (23) for subsequently re-establishing the heating current of the cathodes (13,   14; 16, 17) after it has been cut.