System for lighting fluorescent lamps

Abstract: A system for lighting fluorescent lamps, includes a plurality of fluorescent lamps, a transformer for generating filament voltage and starting voltage of the fluorescent lamps, a switching circuit for sequentially opening and closing a plurality of its contacts every predetermined time, and a driving circuit for electrically biasing the transformer and the switching circuit. Starting voltage is sequentially applied to the fluorescent lamps each independently connected to one of the contacts so that the fluorescent lamps may be sequentially turned on.

Description: The present invention relates to a system for sequentially lighting fluorescent lamps. This system can be preferably employed in a color printer, a color scanner or the like. In an optical reader such as a color printer, a color scanner or the like, tricolor light sources are applied to an original document to be read, sequentially first in red, second in green and third in blue. In this event, the original document is relatively moved with respect to the light sources for the scanning thereof so that reflected light from the light sources may be read out by an image pickup means such as a CCD (charge coupled device) or the like. A plurality of fluorescent lamps each for independently emitting light in one of the aforementioned three colors are generally employed as the light sources. Fig. 1 illustrates an electric circuit of one of the conventional lighting systems. Red, green and blue fluorescent lamps 1, 2 and 3 respectively are connected at their respective filaments R0, G0 and B0 commonly to the first winding 4a of a power transformer 4. The other filaments R1, G1 and B1 of the fluorescent lamps 1, 2 and 3 are independently connected to the second winding 4b, to the third one 4c and to the fourth one 4d of the transformer 4, respectively. The primary winding 4p of the transformer 4 is connected to a driving circuit 5 through a line ℓ1 so as to be electrically biased through the driving circuit 5. The line ℓ1 is also connected to three starting circuits 9, 10 and 11 through contacts S1, S1 and S3 of switching circuits 6, 7 and 8, respectively so as to be electrically biased by the starting circuits 9, 10 and 11. The switching circuits 6, 7 and 8 sequentially connect the line ℓ1 to the starting circuits 9, 10 and 11, and cut the former off the latter by virtue of the driving circuit 5 through a line ℓ2 every predetermined time. The switching circuits 6, 7 and 8 each comprise, for example, relays and the like. In this circuit, a power switch S0 is initially turned on. When the driving circuit 5 has been electrically biased, the transformer 4 is charged with electric current therethrough. In this event, filament voltage V0 common to all the fluorescent lamps 1 to 3 is applied to the filaments R0, G0 and B0 thereof, whereas filament voltage V1, V2 and V3 are independently applied to the other filaments R1, G1 and B1 of the fluorescent lamps 1 to 3, respectively. As a result, the filaments of the red, green and blue fluorescent lamps 1, 2 and 3 respectively are heated and kept on being heated in use. Upon lapse of a period required for preheating the filaments, the driving circuit 5 drives the switching circuits 6, 7 and 8 so that the first, second and third contacts S1, S2 and S3 may be sequentially connected or disconnected every predetermined time. As a result, the first, second and third starting circuits 9, 10 and 11 are sequentially connected to the line ℓ1 so that the first, second and third starting voltage V4, V5 and V6 are sequentially independently applied between both the filaments R0-R1 of the red fluorescent lamp 1, between those G0-G1 of the green fluorescent lamp 2 and between those B0-B1 of the blue fluorescent lamp 3 through current-limiting capacitors C1, C2 and C3, respectively. Consequently, the corresponding fluorescent lamps 1 to 3 are selectively turned on and off so that the scanning and readout of the original document may be conducted with the use of three different colors. In the above described conventional system, however, it is necessary to independently provide three switching circuits 6, 7 and 8 for sequentially lighting the corresponding fluorescent lamps 1, 2 and 3. Since these appliances inevitably occupy considerable space in an apparatus employing therein the conventional system, such an apparatus has been manufactured undesirably at high cost. There has been, therefore, an increased demand for the system for lighting the fluorescent lamps which enables the apparatus of a small size at reduced production cost. Accordingly, the present invention has been developed with a view to substantially eliminating the above described disadvantage inherent in the prior art system for lighting fluorescent lamps, and has for its essential object to provide an improved system for lighting the fluorescent lamps which enables small-sized apparatus at reduced production cost. This problem is solved by a system with the features of Claim 1. Another important aspect of the present invention is to provide a system of the above described type which is simple in construction and stable in functioning. These and other features of the present invention will become more apparent from the following description taken in conjunction with the preferred embodiment thereof with reference to the accompanying drawings, throughout which like parts are designated by like reference numerals, and in which: Fig. 1 is an electric circuit employed in the conventional system for lighting fluorescent lamps, Fig. 2 is an electric circuit employed in the system for lighting the fluorescent lamps according to one preferred embodiment of the present invention; and Fig. 3 is a time-chart showing the operation of the system of Fig. 2. Fig. 2 illustrates an electric circuit of a system for lighting fluorescent lamps according to one preferred embodiment of the present invention. In this embodiment, a plurality of fluorescent lamps, i.e., red, green and blue fluorescent lamps 21, 22 and 23 respectively are provided as light sources. Filaments R10, G10 and B10 of the fluorescent lamps 21, 22 and 23 are commonly connected to the first winding 24a of a transformer 24 which generates filament voltage and starting voltage of the fluorescent lamps 21, 22 and 23. The other filaments R11, G11 and B11 of the fluorescent lamps 21, 22 and 23 are independently connected to the second, third and fourth winding 24b, 24c and 24d of the transformer 24, respectively. The primary winding 24p of the transformer 24 is connected to a driving circuit 25 through a line ℓ11 so as to be electrically biased by an output therefrom. The driving circuit 25 is also connected to a line ℓ12 which is further connected to a switching circuit 26 comprising, for example, relays. The driving circuit 25 is further connected to a power switch S20 so as to be supplied with electric current through it and a line ℓ10. The switching circuit 26 has a plurality of contacts S11, S12 and S13 for sequentially controlling electric connection and cut-off at desired timing described later by virtue of the driving circuit 25. On the secondary side of the transformer 24, is further provided high-voltage winding 24e required for starting the fluorescent lamps. One terminal of the high-voltage winding 24e is connected to one common terminal of the filaments R10, G10 and B10 of the fluorescent lamps 21, 22 and 23, respectively, whereas the other terminal thereof is connected to one common terminal of the contacts S11, S12 and S13 of the switching circuit 26 through a current-limiting capacitor C11. The other terminal of each contact S11, S12 or S13 is independently connected to one terminal of each filament R11, G11 or B11, respectively. Fig. 3 is a time-chart showing the operation of the system of the present invention. At the beginning of the operation, the power switch S20 is initially turned on at the time t0 in Fig. 3(a) so that the driving circuit 25 may be electrically biased. The transformer 24 is then electrically biased through the driving circuit 25. As shown in Fig. 3(e) to 3(h), the filament voltage V10 is applied commonly to the filaments R10, G10 and B10 of the fluorescent lamps 21, 22 and 23, respectively. The filament voltage V11, V12 and V13 are independently applied to the other filaments R11, G11 and B11 of the fluorescent lamps 21, 22 and 23, respectively. In this way, the filaments of the red, green and blue fluorescent lamps 21, 22 and 23 are heated. The filament voltage V10 to V13 are each, for example, 8V. Each filament is continuously heated as far as the time t13 during the use of the fluorescent lamps. Upon lapse of a period T0 from the time t0 to t1 required for preheating the filaments, the switching circuit 26 is electrically biased by the driving circuit 25. In this event, as shown in Figs. 3(b) to 3(d), the first, second and third contacts S11, S12 and S13 are sequentially charged with electric current for predetermined periods T1 from the time t1 to t2, T2 from the time from t3 to t4 and T3 from the time t5 to t6, respectively. Accordingly, as shown in Figs. 3(i) to 3(k), the starting voltage V14 is sequentially independently applied, through the current-limiting capacitor C11, between the filaments R10 and R11, between those G10 and G11 and between those B10 and B11 of the red, green and blue fluorescent lamps 21, 22 and 23, respectively. The starting voltage V14 is, for example, 300V, thereby to sequentially light the fluorescent lamps 21 to 23 at the aforementioned predetermined time. As a result, the fluorescent lamps 21 to 23 are applied to the paper sheet (not shown) so that the scanning and readout thereof may be conducted with the use of three colors. The operation after the time t7 up to the completion time t13 is the same as above. By the above described construction and operation of the present invention, it is not necessary to provide a plurality of starting circuits corresponding to respective fluorescent lamps, as is required in the conventional system. Accordingly, small-sized apparatus can be obtained desirably at reduced production cost. Although the present invention has been fully described by way of examples with reference to the accompanying drawings, it is to be noted here that various changes and modifications will be apparent to those skilled in the art. Therefore, unless such changes and modifications otherwise depart from the scope of the present invention as defined in the appended claims, they should be construed as being included therein.

Claims: A system for lighting fluorescent lamps, comprising: a plurality of fluorescent lamps (21,22,23); a transformer (24) generating a filament voltage (V10,V11,V12,V13) of the fluorescent lamps (21,22,23); a driving circuit (25) for electrically biasing the transformer (24); a plurality of contacts (S11,S12,S13) being sequentially operated by the driving circuit (25) for connecting and disconnecting the lamps (21,22,23) to a starting voltage (V14), only one lamp (21,22,23) being connected at the same time characterized in that the starting voltage (V14) is generated by a single secondary winding (24e) of the same transformer (24) which generates the filament voltage (V10 - V13), and that the contacts (S11,S12,S13) are arranged in a single switching circuit (26). A system according to Claim 1, wherein the winding (24e) is connected to one common terminal of the contacts (S11,S12,S13) of the switching circuit (26) through a single current-limiting capacitor (C11). A system according to Claim 1 or 2, wherein the fluorescent lamps (21,22,23) emit light in red, green and blue, respectively.

Inventors: NAGANO FUMIKAZU, NAGANO, FUMIKAZU
Applicants: SHARP KK, SHARP KABUSHIKI KAISHA
Application year: 1988
Main classification: H05B41
IPC codes: G03B27, H05B41, H05B37