Patent Publication Number: US-6211624-B1

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

Description:
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. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The following FIGS. 1 through 7 serve a better understanding of the inventive thought. They should not be interpreted as limiting and should be understood as exemplary embodiments only. 
     FIG. 1 shows the relationship between the net voltage and the brightness of the fluorescent lamp at full and reduced net voltage with a resistance  25  as the control component. 
     FIG. 1 a  shows the relationship between the net voltage and the brightness of the fluorescent lamp with an electronic circuit element  26  as a current blocking and thus controlling component. 
     FIG. 2 shows the relationship between the net voltage and the brightness of the fluorescent lamp when the brightness is controlled by deactivation impulses. 
     FIGS. 3 and 3 a  show two exemplary embodiments of the circuits under the invention. 
     FIG. 3 b  shows an example of a circuit combination. 
     FIG. 4 shows the form of the input net voltage and of the current with an electronic circuit element  26  as a blocking component. 
     FIG. 5 shows the form of the input net voltage and of the current with a gate circuit as the blocking component. 
     FIG. 6 shows the form of the input net voltage in an external simple embodiment of the electronic circuit element  26  as the blocking component. 
     FIG. 7 shows the form of the input net voltage and of the current with an additional impulse generator as component  7 . 
    
    
     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  1   a  is provided in series with the mains switch  1 . The rest contact of the touch contact is normally closed. If the touch contact  1   a  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  1   a , 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. 1 a  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. 1 a , 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  1   a , selects the desired brightness of the fluorescent lamp  18 . 
     The three embodiments in FIG. 1 a  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&#39; 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. 1 a . 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  1   a  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  1   a  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  1   a  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. 3 b ). Here, too, the design possibilities are endless. Also, a spring controlled switch could be used. 
     LEGEND 
       1  mains switch 
       1   a  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 
       2   x  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