Patent Publication Number: US-2015069931-A1

Title: Scanning light-emitting device with increased light intensity

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This non-provisional application claims priority under 35 U.S.C. §119(a) on Patent Application No. 102216852 filed in Taiwan, R.O.C. on 2013 Sep. 6, the entire contents of which are hereby incorporated by reference. 
     BACKGROUND 
     1. Technical Field 
     The present utility model relates to a scanning light-emitting device, and more particularly, to a scanning light-emitting device with increased light intensity. 
     2. Related Art 
     Copiers, printers, fax machines and multi-function printers (MFPs) use Electro-photography as the core technology of printing files, that is, change distribution of electrostatic charges by light having a particular wavelength to generate photographic images. 
     Referring to  FIG. 1 , a schematic structural view of a color printing light-emitting diode (LED) printer  100  is shown. The LED printer  100  has a photoconductive drum ( 110 K,  110 M,  110 C,  110 Y, generally referred to as  110 ), a printing head ( 120 K,  120 M,  120 C,  120 Y, generally referred to as  120 ) and a toner cartridge ( 130 K,  130 M,  130 C,  130 Y, generally referred to as  130 ) that are respectively corresponding to black, magenta, cyan and yellow. By using a power distribution mechanism, a surface of the photoconductive drum  110  may generate a layer of uniform charges. The scanning process prior to printing requires an exposure process, so that pattern pixels in files to be printed are converted into visible light and dark information. The printing head  120  has a plurality of one-dimensionally arranged light-emitting diodes, when light emitted by the LEDs is irradiated onto the photoconductive drum  110 , unexposed areas may maintain the original potential, but charges of the exposed areas may differ due to exposure. A potential change difference of the exposed area may adsorb toner with positive/negative charges provided by the toner cartridge  130 , thereby achieving the aim of printing. 
       FIG. 2  is a schematic view of sensing of the printer  100 . As shown in  FIG. 2 , the printing device includes a photoconductive drum  110 , a printing head  120  and a lens  150 . The lens  150  is located between the photoconductive drum  110  and the printing head  120 , and is used to focus light emitted from the printing head  120  on the photoconductive drum  110 , so as to implement the foregoing exposure process. 
       FIG. 3  is a schematic top view of the printing head  120 . As shown in  FIG. 3 , the printing head  120  includes a plurality of light-emitting chips  122  arranged along an axis  140 . Generally, each light-emitting chip  122  includes thousands of light-emitting units (e.g., LEDs) linearly arranged. When the light-emitting chips  122  are arranged along the axis  140 , the light-emitting units are also arranged along the axis  140 , so as to achieve high DPI printing resolution. For example, to achieve 600 DPI resolution, it is necessary to arrange 600 light-emitting units in each inch. 
     It can be understood from the above description that, when the printing speed is to be increased, the light-emitting time of each light-emitting unit will be shortened; therefore, how to increase the printing speed while keeping good printing quality is a problem that researchers in this field hope to solve. 
     SUMMARY 
     In view of the above problem, the present utility model provides a scanning light-emitting device with increased light intensity, thereby solving the problem of how to increase the printing speed while keeping good printing quality existing in the prior art. 
     An embodiment of the present utility model provides a scanning light-emitting device with increased light intensity, including a shift circuit and a light-emitting circuit. 
     The shift circuit includes a plurality of shift thyristors, a plurality of diodes and a plurality of shift signal lines. The plurality of shift thyristors is divided into a plurality of groups at intervals. Each of the diodes is electrically connected between two adjacent shift thyristors. Each of the shift signal lines is electrically connected to the shift thyristors belonging to one of the groups, where the number of the shift signal lines is the same as that of the groups. 
     The light-emitting circuit includes a plurality of light-emitting thyristors and a plurality of light-emitting control lines. Each of the light-emitting thyristors is correspondingly electrically connected to one of the shift thyristors. Each of the light-emitting control lines is electrically connected to the light-emitting thyristors electrically connected to the shift thyristors belonging to one of the groups, where the number of the light-emitting control lines is the same as that of the groups. 
     According to the scanning light-emitting device with increased light intensity of the present utility model, a light-emitting term of each light-emitting thyristor can be extended, and thus the total light-emitting intensity of each light-emitting thyristor can be extended in a limited printing term. Accordingly, the printing speed can be improved and the original light-emitting intensity and printing quality can be maintained. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a prior art of a schematic structural view of a color printing LED printer; 
         FIG. 2  is a prior art of a schematic view of sensing of the printer; 
         FIG. 3  is a prior art of a schematic top view of a printing head; 
         FIG. 4  is a circuit diagram of a scanning light-emitting device according to an embodiment of the present utility model; 
         FIG. 5  is a schematic signal view of a scanning light-emitting device according to an embodiment of the present utility model; 
         FIG. 6  is a schematic top view of an integrated circuit of a scanning light-emitting device according to an embodiment of the present utility model; and 
         FIG. 7  is a schematic side view of an integrated circuit of a scanning light-emitting device according to an embodiment of the present utility model. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 4  is a circuit diagram of a scanning light-emitting device  200  according to an embodiment of the present utility model. The scanning light-emitting device  200  with increased light intensity (hereinafter referred to as a scanning light-emitting device for short) of the present utility model may be the foregoing light-emitting chip  122 . 
     As shown in  FIG. 4 , the scanning light-emitting device  200  includes a shift circuit  230  and a light-emitting circuit  250 . The shift circuit  230  includes a plurality of shift thyristors (T 1 , T 2 , T 3  and T 4 , generally called T), a plurality of diodes (D 1 , D 2 , D 3  and D 4 , generally called D) and a plurality of shift signal lines (herein taking two shift signal lines φ 1  and φ 2  as an example). The light-emitting circuit  250  includes a plurality of light-emitting thyristors (L 1 , L 2 , L 3  and L 4 , generally called L) and a plurality of light-emitting control lines (herein taking two light-emitting control lines φI 1  and φI 2  as an example). 
     The shift thyristors T are divided into a plurality of groups at intervals. Therefore, in this embodiment, odd shift thyristors (T 1 , T 3  and the like) are considered as a group (hereinafter referred to as “odd group”), and even shift thyristors (T 2 , T 4  and the like) are considered as a group (hereinafter referred to as “even group”). Each diode D is electrically connected between two adjacent shift thyristors T. Each of the shift signal lines is electrically connected to the shift thyristors T belonging to one of the groups. For example, the shift signal line φ 1  is electrically connected to each of the shift thyristors (T 1 , T 3  and the like) of the odd group; and the shift signal line φ 2  is electrically connected to each of the shift thyristors (T 2 , T 4  and the like) of the even group. Therefore, the number of the shift signal lines is the same as that of the groups. 
     Each of the light-emitting thyristors T is correspondingly electrically connected to one of the shift thyristors T. That is, a light-emitting thyristor Ln is electrically connected to a shift thyristor Tn, where n is a positive integer. For example, a light-emitting thyristor L 1  is electrically connected to a shift thyristor T 1 , and a light-emitting thyristor L 2  is electrically connected to a shift thyristor T 2 . Each of the light-emitting control lines is electrically connected to the light-emitting thyristors L electrically connected to the shift thyristors T belonging to one of the groups. For example, a light-emitting control line φI 1  is electrically connected to a light-emitting thyristor L connected to a shift thyristor T in the odd group (hereinafter referred to as the light-emitting thyristor of the odd group); a light-emitting control line φI 2  is electrically connected to a light-emitting thyristor L connected to a shift thyristor T in the even group (hereinafter referred to as the light-emitting thyristor of the even group). Herein, the number of the light-emitting control lines is also the same as that of the groups. 
     Each shift thyristor T includes a first anode end  31 , a first cathode end  32  and a first gate end  33 ; each light-emitting thyristor L includes a second anode end  34 , a second cathode end  35  and a second gate end  36 . The shift thyristors T and the light-emitting thyristors L electrically connected with each other are electrically connected through respectively the first gate end  33  and the second gate end  36 . Two ends of each of the diodes D are respectively electrically connected to the first gate end  33  of two adjacent shift thyristors T. For example, an anode end of a diode D 1  is electrically connected to the first gate end  33  of the shift thyristor T 1 , and a cathode end thereof is electrically connected to the first gate end  33  of another shift thyristor T 2 . Each shift thyristor T is electrically connected to the corresponding shift signal line with the first cathode end  32  thereof, and the first anode end  31  of each shift thyristor T is grounded. Similarly, the second cathode end  35  of each light-emitting thyristor L is electrically connected to the corresponding light-emitting control line, and the second anode end  34  of each light-emitting thyristor L is grounded. 
     The shift circuit  230  further includes a pulldown signal line V GA , an initial signal line φS and a plurality of load resistors (R 1 , R 2 , R 3  and R 4 , generally called R). The first gate end  33  of each shift thyristor T is electrically connected to a load resistor R (for example, the first gate end  33  of the shift thyristor T 1  is electrically connected to the load resistor R 1 ). One end of the load resistor R is electrically connected to the first gate end  33 , and the other end is electrically connected to the pulldown signal line V GA . The pulldown signal line V GA  provides a pulldown voltage level (herein it is a negative potential) for the load resistors R, so that the first gate end  33  and the first anode end  31  of the actuating shift thyristor T can have a forward bias therebetween. The initial signal line φS is electrically connected to the first gate end  33  of the first shift thyristor T 1 , so as to feed a single pulse (as shown in  FIG. 5 ) actuated by triggering sequential shifting of the shift circuit  230 . 
       FIG. 5  is a schematic signal view of a scanning light-emitting device  200  according to an embodiment of the present utility model, which schematically shows a timing relation of signals fed by the signal line or control line. 
     As shown in  FIG. 5 , after the initial signal line φS feeds the single pulse, two shift signal lines φ 1  and φ 2  respectively feed pulse signals with substantially the same pulse width but a phase difference being between 90 degrees to 180 degrees. Therefore, in coordination with the shift circuit  230  as shown in  FIG. 4 , the first anode end  32  of the shift thyristor T can be sequentially changed into a low voltage level along a forward conduction direction of the diode D. Because the second gate end  36  of the light-emitting thyristor L is connected to the first gate end  33  of the shift thyristor T, the second gate end  36  of the light-emitting thyristor L may also be sequentially actuated following the shift thyristor T. When the first anode end  32  of the next shift thyristor T (or the second anode end  35  of the light-emitting thyristor L) has been changed into a low voltage level for a period of time, the first anode end  32  of the previous shift thyristor T (or the second anode end  35  of the light-emitting thyristor L) is restored to a high voltage level. Herein, the high voltage level is a ground level (i.e., 0 V), and the low voltage level is a negative level (e.g., −5 V). 
     The characteristic of a thyristor such as the shift thyristor T and the light-emitting thyristor L is as follows: when a forward bias is applied between an anode and a cathode and a breakdown voltage exceeding a PN junction is applied between a gate and the cathode, the thyristor may be conducted, and after a bias between the gate and the cathode is removed, the thyristor may still maintain a conducted state, and it is restored to a non-conducted state until the forward bias between the anode and the cathode disappears. Therefore, when the first gate end  33  of the shift thyristor T 1  receives a first low level pulse of the shift signal line φ 1  and starts, the corresponding light-emitting thyristor L 1  also starts and emits light because it also receives a first low level pulse fed by the light-emitting control line φI 1 , and after the first low level pulse of the shift signal line φ 1  ends, it can continuously emit light, until the first low level pulse fed by the light-emitting control line φI 1  ends, so that it can continuously emit light in a light-emitting term t1. Similarly, the light-emitting thyristors L 2 , L 3  and L 4  respectively emit light in light-emitting terms t2, t3 and t4. 
     As shown in  FIG. 5 , each of the light-emitting control lines φI 1  and φI 2  feeds a light-emitting signal having a plurality of low voltage level intervals, and the low voltage level intervals of the light-emitting signals fed by the two light-emitting control lines φI 1  and φI 2  corresponding to the adjacent groups are partially overlapped. An intermittent interval (i.e., a high voltage level interval) between two adjacent low voltage level intervals of each light-emitting signal corresponds to the low voltage level interval of the adjacent light-emitting signal. That is to say, two light-emitting control lines φI 1  and φI 2  may respectively control light-emitting terms of the light-emitting thyristors L of the odd group and the even group, and thus the light-emitting terms of the light-emitting thyristors L of the odd group and the even group can be partially overlapped. Therefore, the light-emitting term of each light-emitting thyristor L can be extended, and the total light-emitting intensity of each light-emitting thyristor L can be extended in a limited printing term. Accordingly, the printing speed can be improved and the original light-emitting intensity and printing quality can be maintained. 
     Herein, although the high voltage level in the text is a ground level (i.e., 0 V), and the low voltage level is a negative level (e.g., −5 V), persons skilled in the art can reverse polarities of the elements and can change the high voltage level into a positive voltage level (e.g., 5 V), and change the low voltage level into a ground level. 
       FIG. 6  is a schematic top view of an integrated circuit of a scanning light-emitting device  200  according to an embodiment of the present utility model.  FIG. 7  is a schematic side view of an integrated circuit of a scanning light-emitting device  200  according to an embodiment of the present utility model. 
     Referring to  FIG. 6  and  FIG. 7  together, the shift thyristors T and the light-emitting thyristors L may be a PNPN construction formed by sequentially laminating a first conductive type epitaxial layer  41 , a second conductive type epitaxial layer  42 , a first conductive type epitaxial layer  43 , and a second conductive type epitaxial layer  44  on a first conductive type substrate  40 . 
     Herein, the first conductive type substrate may be of a GaAs material, and the first conductive type epitaxial layer and the second conductive type epitaxial layer may be of an AlGaAs material. 
     Referring to  FIG. 4 ,  FIG. 6  and  FIG. 7  together, the first gate end  33  of the shift thyristor T, the second gate end  36  of the light-emitting thyristor L and the anode end of the diode D are connected with each other, and thus the shift thyristor T, the light-emitting thyristor L and the diode D share the same ohmic electrode  51 . The ohmic electrode  51  is formed on the first conductive type epitaxial layer  43 . The diode D is composed of the first conductive type epitaxial layer  43  and the second conductive type epitaxial layer  44  sequentially laminated on the second conductive type epitaxial layer  42 . Moreover, the cathode end of the diode D has an ohmic electrode  52 , which is formed on the second conductive type epitaxial layer  44 . The first cathode end  32  of the shift thyristor T has an ohmic electrode  53 , which is formed on the second conductive type epitaxial layer  44 . The second cathode end of the light-emitting thyristor L has an ohmic electrode  54 , which is formed on the second conductive type epitaxial layer  44 . Herein, the second conductive type epitaxial layers  44  of the diode D, the shift thyristor T and the light-emitting thyristor L are not connected with each other. 
     The resistor R may be formed by another first conductive type epitaxial layer  41 , another second conductive type epitaxial layer  42 , and another first conductive type epitaxial layer  43  sequentially laminated on the first conductive type substrate  40 . Moreover, two ohmic electrodes  55  are formed on the first conductive type epitaxial layer  43 , which can serve as two ends of the resistor R, so as to be connected to other elements or signal lines. 
     In an embodiment, a Schottky barrier diode D can be formed through direct Schottky contact with the first conductive type epitaxial layer  43  through wiring. 
     In the above construction, the first conductive type is a P type, and the second conductive type is an N type, but embodiments of the present utility model are not limited thereto. In some embodiments, the first conductive type may be the N type, the second conductive type may be the P type, and the polarities of the cathode and the anode are opposite. 
     According to the scanning light-emitting device with increased light intensity of the present utility model, a light-emitting term of each light-emitting thyristor L can be extended, and thus the total light-emitting intensity of each light-emitting thyristor L can be extended in a limited printing term. Accordingly, the printing speed can be improved and the original light-emitting intensity and printing quality can be maintained. 
     While the present invention has been described by the way of example and in terms of the preferred embodiments, it is to be understood that the invention need not be limited to the disclosed embodiments. On the contrary, it is intended to cover various modifications and similar arrangements included within the spirit and scope of the appended claims, the scope of which should be accorded the broadest interpretation so as to encompass all such modifications and similar structures.