Method and device for the modulation of the intensity of fluorescent lamps

The invention describes a method for the modulation of the light intensity of fluorescent lamps via the supply main by modification of the form and/or the amplitude of the power supply provided. An electronic control element, provided as a component of the logical circuit, temporarily blocks current flow after at least every second zero-crossing of the voltage, dependent upon time and/or voltage. Blocking of the current flow occurs only during the time period in which there is no flow of charging current for the downstream direct-current mains supply circuit. The advantage thus obtained is that the control pulses for the logical circuit do not influence the electric current flowing through the fluorescent lamps.

BACKGROUND OF THE INVENTION
 Because fluorescent lamps cannot be simply dimmed with a phase control like
 incandescent lamps, numerous suggestions have been made for reducing the
 brightness by means of group circuits or other methods in residential or
 business quarters.
 This applies especially to fluorescent compact lamps where the fluorescent
 lamp with a ballast is inserted in the normal lamp socket and therefore
 only the two mains supply lines are available for modulating the
 brightness.
 For example, the German patent DE 40 37 948 described an arrangement where
 the compact lamp is switched to two bi-stable switching conditions by
 short interruptions of the power supply. This arrangement was used in
 practice but is not satisfactory because it is not adequately comparable
 with the function of a continually controllable dimmer.
 U.S. Pat. No. 5,068,576 introduced another dimmer switch for a fluorescent
 lamp where a simple two-wire connection is arranged between the dimmer
 switch and the fluorescent lamp. The control of the logical circuit is
 performed via the change of the input voltage of a voltage regulator. A
 microcomputer influences the voltage amount through digital signals. A
 phase cutting control was described where complete half waves are cut off
 from the mains alternating voltage. This entails the disadvantage that the
 cut half waves cause the fluorescent lamp to flicker when dimmed.
 SUMMARY OF THE INVENTION
 It is the task of this invention to propose a method for dimming
 fluorescent lamps that is extremely simple to operate, that has a far
 simpler arrangement and where the fluorescent lamp is not additionally
 influenced by the control impulses of the logical circuit.
 This invention makes this possible by using an electronic control element
 as a component of the logical circuit in which the block of the current
 flow occurs only during the time period when there is no charging current
 for the downstream current mains supply circuit. This has the advantage
 that control of the logical circuit do not influence the electric current
 flowing through the fluorescent lamp. Unwanted influences on the light
 intensity of the fluorescent lamp by control pulses for the logical
 circuit are thus avoided.
 A preferred embodiment for changing the form of the input voltage is that
 an electronic circuit element is provided as a component which temporarily
 blocks the current flow at least after every second zero-crossing of the
 voltage, depending upon time and/or voltage. This circuit does not
 influence the current supply of the fluorescent lamp when the current flow
 block occurs only during the time period in which there is no flow of
 charging current for the downstream direct-current mains supply circuit.
 An impulse generator is suggested as another variant for changing the input
 voltage form that emits its identification impulses only during the time
 period when there is no charging current for the downstream direct-current
 mains supply circuit. This embodiment also insures that the identification
 impulses do not interfere with the power supply of the fluorescent lamp
 during the brightness adjustment.
 In order to prevent influencing the intensity dimmer during brief mains
 interruptions below 100 milliseconds as they can occur with lightening
 strikes, the logical circuit can also be blocked during such mains
 interruptions.
 Because a continual control of the light intensity is not desired in many
 cases, a logical circuit under this invention can be designed in the
 manner that the logical circuit controls a gradual reduction of brightness
 to default brightness levels when the current flow is briefly interrupted
 for more than 100 milliseconds.
 The combination of the two features for controlling the logical circuit,
 namely providing for a change of the net voltage change and also for a
 brief interruption of the mains supply, is optionally available, for
 example, in a single contact lamp. This means an important simplification
 of such circuits because these dimmer circuits can be directly integrated
 in the upstream device.
 Such dimming cannot reach brightness 0. For this reason, the invention
 suggests that brightness is again increased after reaching a certain
 minimum brightness during a longer change of the net voltage.
 When full brightness is reattained, the invention provides that even in
 continued net voltage changes the full brightness is maintained and no
 further reduction phase of brightness occurs.
 This measure is necessary to avoid a stronger decrease and increase of
 brightness during an unwanted decrease of the net voltage, for example at
 peak consumption. With the suggested measure, such net behavior would
 indeed introduce a dimming process which, however, would be leveled after
 a short period of time.
 The change of input net voltage can be accomplished under the invention by
 installing a touch contact in series with the net circuit that has a
 normally closed rest contact bridging a component that changes the form
 and/or the amplitude of the input net voltage.
 A resistance is proposed as an alternative form of such a component which
 changes only the amplitude of the input voltage. A relatively small
 voltage decrease suffices to trigger the logical circuit so that the
 voltage decrease in the brief period of activation plays practically no
 role. But the fluorescent lamp receives less power during the brightness
 control adjustment so that the adjustment suffers a minor distortion when
 no voltage control occurs in the direct-current mains supply circuit or in
 the converter.
 To implement the process described above, no complicated dimmer is required
 as before but rather a touch contact is provided in series with the net
 circuit containing a normally closed rest contact that bridges a
 resistance or a simple electronic element.
 This is completely adequate to control the logical circuit that can be
 integrated with the electronic upstream device in a common housing
 resulting in a contact lamp or a contact lamp adapter, respectively, where
 a threaded socket or a quarter-turn type connector makes the insertion
 into a lamp fixture possible.
 The fluorescent lamp can be optionally connected firmly with, or plugged
 into such a compact lamp housing.
 It is also recommended to combine the mains switch and the touch contact
 into one unit or, also, to provide the mains switch directly with an
 additional rest contact that is formed as a touch contact.

The schematic figures are explained below in detail.
 DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT
 The circuit embodiment FIG. 3 shows that an additional touch contact 1a is
 provided in series with the mains switch 1. The rest contact of the touch
 contact is normally closed. If the touch contact 1a is activated, a
 voltage decrease occurs at resistance 25 and the voltage input to the
 directcurrent mains supply circuit 11 is changed, i.e., the amplitude is
 reduced in this case.
 The logical circuit 12 receives this information via the lines 15 and
 reacts, for example, as shown in the diagram of FIG. 1. This diagram shows
 the voltage in the lower part and the corresponding brightness of the
 fluorescent lamp in the upper part. The manner in which the logical
 circuit converts the received information into brightness values will be
 discussed later.
 With the first activation of the mains switch 1 at the point in time 6, the
 fluorescent lamp 18 receives its full brightness 2. As long as a circuit
 pause 5 is defaulted by activating the contact 1a, the logical circuit 12
 regulates the brightness of the fluorescent lamp downward. The brightness
 reaches a mean value 3 in this example. At the points 6, at first a minor
 reduction and at the end of the control process a minor increase in
 brightness can be observed because the resistance 25 reduces the input net
 voltage during this time. Considering the modest cost of such a device,
 this barely noticeable deviation is undoubtedly acceptable.
 In the first example FIG. 1, a second switching pause 5 is shown that leads
 to a continued reduction of the brightness. Because this second switching
 pause 5 is shorter than the first, the proportional reduction of
 brightness is also smaller. Here, too, the deviation of the brightness
 levels during the control process is visible in the points 6.
 The second example in FIG. 1 shows what happens in a sudden voltage
 reduction of a longer duration that may be caused by the net, for example.
 The logical circuit 12 holds the signal initially for a command to reduce
 the brightness and begins with a continual dimming at point 6. Because the
 supposed signal continues, the brightness sinks to the lowest default
 value 4. The invention provides that the brightness again increases when
 this lowest brightness limit is reached. Either the signal ends or the
 maximum brightness value is reached. The invention provides that the
 dimming ends at this point to prevent that a continual alteration of the
 brightness occurs. If the decreased net voltage remains, the maximum
 brightness reaches only the reduced value shown in FIG. 1.
 After a longer pause 9, the lamp is lit at the then possible maximum
 brightness independent from the previously set brightness.
 The illustrated short pause 13 below 100 milliseconds, for example, as it
 would sometimes occur in power outages, does not influence the brightness.
 The variant shown in FIG. 1a reflects an invented process where an
 electronic circuit element 26 is provided instead of the resistance 25.
 The circuit element transmits the dimming command to the logical circuit
 12 at a time when no charging current flows to the downstream
 direct-current mains supply circuit 11, as illustrated in FIGS. 4 through
 7.
 This is explained as follows: In direct-current mains supply circuits, a
 charging condenser 27 is charged from the alternating-current circuit via
 a rectifier circuit 24 and supplies the required current generally via a
 converter 10 to the fluorescent lamp 18. However, current from the net can
 only charge the condenser via the rectifier circuit 24 when the momentary
 value of the alternating voltage is higher than the direct voltage at the
 charging condenser 27.
 This, however, only applies to a small areas of the alternating-current
 half waves, as shown in FIGS. 4 and 5. Accordingly, the current flows only
 in the comparatively short positive and negative current peaks 28. In the
 intermediate times, the net voltage can be freely changed or modulated
 with impulses without influencing the current intake of the fluorescent
 lamp and without influencing its brightness.
 With reference to FIG. 1a, this means that information can be sent to the
 logical circuit 12 with electronic circuit elements 26 without influencing
 the power supply of the rectifier mains 11. The electronic circuit
 elements 26 interrupt the net voltage at every zero-crossing of the
 voltage for a brief time, depending upon time and/or voltage, as shown in
 FIG. 4. The duration of this information, corresponding with the
 activation of the touch contact 1a, selects the desired brightness of the
 fluorescent lamp 18.
 The three embodiments in FIG. 1a correspond with those in FIG. 1 but do not
 show the unwanted brightness deviations at the points 6.
 The same brightness control without deviations is also possible with other
 electronic devices 26 whose functions are shown in FIGS. 5, 6 and 7. FIG.
 5 shows the function of an electronic gate switch. It opens the current
 gate only in certain segments of the alternating-current half waves. These
 current gates are marked with x in FIG. 5. It is easy for the logical
 circuit to determine if the gate function is activated or not. The
 duration of the progressive dimming proceeds accordingly.
 The diagrams in FIGS. 4 through 7 show the possible current flow times as
 dotted areas 29 in the sinus-shaped voltage line 31.
 An additional modulation with overlapping impulses 32 at higher
 frequencies, as shown in FIG. 7, can only recommended for especially
 demanding solutions. In most cases, even a change of the two half waves is
 not needed. This applies to all examples cited.
 For completeness' sake, an additional modulation or an emission of impulses
 with higher frequencies is shown during the touch pauses 5 with the shaded
 areas in FIG. 1a. It is understood that an influence on the brightness
 through short interruptions is impossible in circuits of this type.
 FIG. 6 shows how such an extremely simple circuit can function under the
 invention by only affecting one half wave and still causing an adequate
 change of the form of the net current to activate the logical circuit 12.
 It is of equal value for the invented process whether the areas 29 of the
 voltage carrying areas or the activation and deactivation flanks 30 of the
 electronic circuit elements 26 are used as the information for the logical
 circuit 12. The described solutions are only intended as examples for all
 circuits functioning in the same manner.
 The German patent application DE 129 29 207.7 described a gradual
 brightness adjustment through an interruption of the net voltage. Its
 function is illustrated in FIG. 2. The principle difference lies the fact
 that after each short interruption 5 exceeding 100 milliseconds, the
 fluorescent lamp must be extinguished and relit. The relighting occurs
 with full current at point 6 to attain a full lighting, but the brightness
 is dimmed gradually in two steps 3 and 4, for example, by interrupting
 twice at the points 8. The brightness levels are cyclically controlled.
 After longer pauses 9, the full brightness is activated, regardless of the
 previously activated level.
 This circuit cannot be compared with the invention under discussion, but
 its combination with a gradual process brings significant advantages. If
 the logical circuit is designed so that it reacts to both signal types,
 namely "change of form and/or of net voltage amplitude" and "interruption
 of net voltage," the brightness of a compact lamp of this type can be
 regulated with all described processes and advantages. Because the logical
 circuit 12 can only be an integrated circuit, such a combination would
 barely entail additional costs, but this synergistic effect makes the lamp
 significantly more advantageous. The model streamlining allows for
 significant cost savings through the universal use of a single lamp type.
 The common functions of the individual components will be discussed on the
 example illustrated in FIG. 3 to explain the invention.
 The net voltage from the net N--N reaches the direct-current mains switch
 11 via the main switch 1 and the touch switch 1a with the parallel
 resistance 25 or an electronic circuit 26. The direct-current mains switch
 supplies the core of the upstream device, the converter 10, with current
 via the lines 14. The logical circuit 12 receives its information which
 brightness level is desired from the net with its downstream components.
 The logical circuit 12 has the task of recognizing and interpreting the
 changes or interruptions caused by the touch switch 1a or the net switch 1
 in order to transmit the corresponding commands via the lines 22 and 23 to
 the converter 10. Of the multitude of possibilities to modulate the
 brightness of a fluorescent lamp 18, a proven embodiment of an DC/AC
 converter with two opposing field effect transistors 20 and 21 is offered
 as an example. The converter 10 converts the direct voltage supplied by
 the direct- current mains supply circuit 11 in a high frequency
 alternating voltage that is delivered via the lines 16 to the heated
 cathodes 17 with the condenser 19 arranged in series. As soon as the
 cathodes 17 are sufficiently heated and ready for emission, the
 fluorescent lamp 18 is lit.
 The brightness of the fluorescent lamp 18 depends essentially on the
 provided effective electric current. This can be regulated by the
 frequency but also by the touch ratio of the half waves of transistors 20
 and 21. Both can be controlled by an integrated circuit 33 which is a part
 of the logical circuit 12. All circuit details are part of the standard
 knowledge of any electronic specialist and require no further explanation.
 They can also be looked up in a textbook.
 A special advantage of the invention lies in the fact that no dimmer or
 special device is necessary. Only an additional touch switch 1a with a
 resistor 25 or a minute electronic circuit 26 is required to change the
 traditional incandescent lamps to dimmable fluorescent lamps under the
 invention.
 The components resistor 25 or electronic circuit 26 are so small that they
 can be housed, according to the invention, in a normal double toggle
 switch that also contains the power switch 1 as well as touch switch which
 simplifies operation (see FIG. 3b). Here, too, the design possibilities
 are endless. Also, a spring controlled switch could be used.
 LEGEND
 1 mains switch
 1a touch contact
 2 full brightness
 3 medium brightness
 4 low brightness
 5 touch pause
 6 point
 7 component
 8 ramp
 9 longer disconnect pause
 10 converter
 11 direct-current mains supply circuit
 12 logical circuit
 13 short interruption
 14 lines
 15 lines
 16 lines
 17 heated cathodes
 18 fluorescent lamp
 19 condenser
 20 MOS-FET (metal oxide semiconductor field effect transistor)
 21 circuit symmetrical MOS-FET
 22 line
 23 line
 24 rectifier circuit
 25 resistance
 N--N alternating-current net
 2x gates
 26 electronic circuits
 27 charging condenser
 28 current peaks
 29 areas
 30 flanks
 31 sinus-shaped voltage lines
 32 superimposed impulses
 33 IC integrated circuit
 34 double toggle switch