JPH0622107A - Led drive circuit device with gradation control - Google Patents

Abstract

(57) [Abstract] [Purpose] LED lighting time can be controlled variably and L
(EN) Provided is an LED drive circuit device with gradation control, which does not increase the circuit scale of the entire ED drive circuit device and has good printing quality. [Structure] Storage means 1 and 2 for storing data for controlling lighting and extinction of a light emitting element 7 and control of a lighting time, and counting means 12 for performing a counting operation with a clock signal supplied.
A comparing circuit 11 for comparing the magnitude of the data sent by the counting means with the data sent by the storing means; and a switch means 6 for controlling the turning on and off of the light emitting element based on the output signal of the comparing circuit. It is characterized by having.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention controls the gradation of print density by controlling the lighting time of a light emitting diode (hereinafter referred to as an LED), which is a component of a printing device provided in a copying machine, a printer, a facsimile, and the like. With gradation control L function
The present invention relates to an ED drive circuit device.

[0002]

2. Description of the Related Art In a printer using an LED as a component of a printer provided in a copying machine, a printer, a facsimile, etc., the so-called γ characteristic, which is the relationship between the lighting time of the LED and the print density, is shown in FIG. It is shown by a curved line. If the number of bits of the data for driving the LED is, for example, 4 bits, the gradation, which is the density of the print density, is divided into 16 steps from gradation 0 to gradation 15 from the lower print density to the higher print density. . In such a case, as is apparent from FIG. 6, in the low gradation range, the change amount of the print density is large with respect to the change amount of the gradation, but in the high gradation range, the change of the print density is large even if the gradation is largely changed. The change is small. Therefore, the LED
If the lighting times of are at regular intervals, the print density hardly changes on the high gradation side even if the gradation is changed. In other words, the number of bits of LED driving data is 4
Even if it is composed of bits, the actual gradation becomes about 8 gradations, and for example, when the density difference of 16 gradations is required, it is necessary to increase the number of bits of the LED driving data to 5 bits or the like.

In order to solve such a problem and change the print density, the driving portion of the LED is devised so that the gradation is changed. (1) A clock signal having an equal signal period is used. The supplied output data of the counter is compared with the output data of the latch that stores the γ-corrected data, which is the data for controlling the turning on / off of the LED and the lighting time, for each bit, and each bit data is compared. If they match, the LED is turned on, and if they do not match, L
ED is turned off, (2) LED is kept on or off until the output data of a counter supplied with a clock signal having a non-equidistant signal period and the latch output data match. There are two known methods. As described above, the γ correction is not proportional to the LED lighting time and the print density as described above. Therefore, in accordance with the γ characteristic, data such as the LED lighting time corresponding to each gradation is obtained in advance, and A table of compensation data is stored in a ROM (read-only memory), and the LED lighting time data corresponding to the gradation is obtained by accessing the ROM.

The above method (1) is processed by, for example, an LED driving device having a circuit configuration shown in FIG. That is, the output side of the 4-bit shift register 1 to which the γ-corrected 4-bit data including the information such as the LED lighting time is supplied while being shifted by the shift clock is supplied from the shift register 1. It is connected to a 4-bit latch circuit 2 which latches data and outputs it as 4-bit parallel data, D0 to D3. The respective output terminals for transmitting the data D0 to D3 are connected to the respective input sides of the AND circuits 4a to 4d. On the other hand, a counter 3 which is supplied with a clock signal having an equal interval shown in FIG. 9A, performs a counting operation based on the clock signal, and outputs the count value in parallel as count data composed of 4-bit data Q0 to Q3. Each output terminal is an output terminal q that sends out data Q0.
0 is connected to the input side of the AND circuit 4a, and the data Q
The output terminal q1 for sending 1 is connected to the input side of the AND circuit 4b, the output terminal q2 for sending data Q2 is connected to the input side of the AND circuit 4c, and the output terminal q3 for sending data Q3 is the AND It is connected to the input side of the circuit 4d. The output side of these AND circuits 4a to 4d is N
The output side of the NOR circuit 5 is connected to the input side of the OR circuit 5, and the output side of the NOR circuit 5 is a P-channel MOS that controls the current supply to the LED 7.
It is connected to the gate of the transistor 6. As is apparent from FIG. 7, the above circuit configuration corresponds to one LED, and in reality, a plurality of the above circuit configurations are provided corresponding to a plurality of LEDs.

In such a circuit, the counter 3 has a value of 0.
Counting is performed by sequentially increasing the count value from 1 to 15,
On the basis of the clock signal having an even interval shown in FIG. 9, signals corresponding to the count value are output terminals q0 to q3 as shown in FIG.
Send out. For example, when the LED 7 is turned on with a light amount corresponding to the fifth gradation, that is, when "5" is designated by the output data D0 to D3 of the latch circuit 2,
When the count value of the counter 3 reaches "5", that is, in FIG.
As shown in (f), the data Q0 and the data Q2 become 1, and the data of 1 is sent out from the AND circuits 4a and 4c.
Data of 0 is transmitted from the OR circuit 5. Therefore,
While 0 data is being sent from the NOR circuit 5, that is, during 5 cycles of the clock supplied to the counter 3, MO
The S transistor 6 is turned on, and the LED 7 lights up.

The method (2) is processed by the LED driving device having the circuit configuration shown in FIG. 8, for example.
In FIG. 8, the same components as those shown in FIG. 7 are designated by the same reference numerals, and the description thereof will be omitted. Data D0
The respective output terminals of the latch circuit 2 for transmitting the signals D3 to D3 are connected to the respective input sides of the EXNOR circuits 8a to 8d. On the other hand, the output terminal q0 for transmitting the data Q0 is the above-mentioned EXN for each output terminal of the counter 3.
The output terminal q1 connected to the input side of the OR circuit 8a and transmitting the data Q1 is connected to the input side of the EXNOR circuit 8b, and the output terminal q2 transmitting the data Q2 is connected to the EXN.
An output terminal q3 connected to the input side of the OR circuit 8c and transmitting the data Q3 is connected to the input side of the EXNOR circuit 8d. The output sides of these EXNOR circuits 8a to 8d are connected to the input side of the AND circuit 9, and the output side of the AND circuit 9 sends the set state data until the reset signal is supplied after the set signal is supplied. Connected to the reset signal input terminal of the flip-flop 10, and the output side of the flip-flop 10 is connected to the gate of the MOS transistor 6. As is clear from the figure, the above circuit configuration corresponds to one LED, and in reality, a plurality of the above circuit configurations are provided for a plurality of LEDs.

In the circuit configured as described above, the data of 1 is sent from the AND circuit 9 only when the output data D0 to D3 of the latch circuit 2 and the output data Q0 to Q3 of the counter 3 are all 0 or 1. Then, the flip-flop 10 is reset and the flip-flop 10
The MOS transistor 6 is turned on or off in response to the output signal of the above, and the LED 7 is turned on or off.

[0008]

However, in the conventional LED drive circuit shown in FIG. 7 described above, since it is necessary to supply the γ-corrected data to the shift register 1 as described above, the above-mentioned ROM and An accompanying circuit such as a data reading device for reading data from the ROM is required,
For example, there is a problem in that the number of latches or shift registers is increased corresponding to the number of A3 size LED driving devices of 4,700, which causes an increase in the circuit scale of the entire printing device. Further, there is a problem that the gradation of the normal print density cannot be displayed unless the cycle of the clock signal supplied to the counter 3 is constant.
That is, as shown in FIG. 10A, when the clock signals supplied to the counter 3 have unequal intervals,
The lighting time of the LED when the latch circuit 2 sends the data corresponding to the gradation 3 as shown in FIG.
As shown in (4), there occurs a phenomenon in which the LED lighting time when the data corresponding to the gradation 4 is transmitted is reversed despite the increase in the gradation. Therefore, the cycles of the clock signals supplied to the counter 3 must be evenly spaced.

On the other hand, in the conventional LED drive circuit shown in FIG. 8 described above, the flip-flop 10 sends out signals of the same level unless the reset signal is supplied from the AND circuit 9, so that the flip-flops 10 are arranged at unequal intervals. The clock signal is supplied to the counter 3 and LE is supplied in response to the clock signal.
The lighting time of D7 can be controlled. Therefore,
Compared to the LED drive circuit shown in FIG. 7, a circuit related to γ correction is not required, but on the other hand, the flip-flop 10 is required, and as a result, the circuit scale of the entire LED drive device is also large.

It should be noted that the LEDs are set to have non-equidistant clock cycles.
Proposals for controlling the on / off time of the LED and changing the amount of light emission by changing the current supplied to the LED are disclosed in, for example, Japanese Utility Model Laid-Open No. 59-149300 and Japanese Patent Laid-Open No. 62-2612.
74, JP-A-63-33056, JP-A-6
It is disclosed in Japanese Laid-Open Patent Publication No. 3-319167. However, even in the invention disclosed in, for example, Japanese Patent Laid-Open No. 62-261274, the LE is set with the periods of the clock signals being non-uniform.
Although changing the lighting time of D is disclosed, the specific configuration of the circuit portion to which the clock signal is supplied and which actually drives the LED is not disclosed.

Furthermore, in a printing apparatus using an LED, in a normal printing state, the photosensitive drum and the recording paper provided in the printing apparatus are moving even when the LED is lit, and the conventional LE is used.
In the D drive device, if the center of the LED lighting time shifts for each gradation, the printing center shifts, and the quality of printed characters and the like deteriorates. That is, FIG. 11 shows a device in which LEDs are arrayed from the left to the right in the drawing, and when the rotation direction of the photosensitive drum is planarly expressed, the LEDs a through It is assumed that the range of toner adhering to the photosensitive drum is indicated by the lighting of e. 7,
Since the counter provided in the conventional LED driving device shown in FIG. 8 is an up counter, the LEDs a to e start lighting at the same time. When the LEDs a to e are controlled so that the lighting time becomes longer in this order, since the photosensitive drum is rotating, the toner adhesion range is from LEDa to LE.
The length becomes longer toward De. Therefore, the center of the toner adhesion range moves from the upper left to the lower right as shown in the figure. Such movement of the center causes the center of the printed character or the like to be displaced, which deteriorates the quality of the printed character or the like.

The present invention has been made in order to solve the above-mentioned problems, and it is possible to variably control the lighting time of the LED, the circuit scale of the entire LED drive circuit device does not increase, and the printing quality is further improved. It is an object of the present invention to provide an LED drive circuit device with good gradation control.

[0013]

SUMMARY OF THE INVENTION The present invention comprises storage means for storing data for controlling lighting and extinguishing of a light emitting element and control of a lighting time, and counting means for performing a counting operation with a clock signal supplied. A comparing circuit for comparing the magnitude of the data sent by the counting means and the data sent by the storing means, and a switch means for controlling turning on and off of the light emitting element based on an output signal of the comparing circuit. It is characterized by that.

[0014]

The counting means is supplied with a clock signal having a non-equidistant period or an equal interval period, the counting means performs a counting operation based on the clock signal, and sends the count value to the comparison circuit. The comparison circuit compares the count value with the data sent from the storage means by, for example, subtracting the data from the count value, and switches the data of, for example, 0 when the count value is larger. Send to the means. Therefore, the data sent from the comparison means to the switch means is
The comparison result is based on the comparison result in the comparison circuit, and the comparison result is based on the count value, and the count value is based on the cycle of the clock signal. Therefore, the storage means, the counting means, and the comparison circuit operate so as to control the turning on and off of the LED in the cycle of the clock signal. Further, since the output signal of the comparison circuit directly controls the operation of the switch means for switching ON / OFF of the LED, the comparison circuit does not need to be provided with another circuit for controlling the switch means, thereby reducing the circuit scale. Acts like. Further, since the comparison circuit compares the count value with the data sent by the storage means, the counting order of the count values supplied to the comparison circuit is up-count, down-count,
Alternatively, either up-down counting may be used. Therefore, according to the counting order of the count values supplied to the comparison circuit, the LED can be turned on and off
Acts to improve print quality.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As shown in FIG. 1, an LED drive device 21 of the present invention comprises a plurality of Ls arranged in a line along the longitudinal direction.
It is provided in the printing device 20 equipped with the ED 7, and the LED 7 is provided based on the signals such as control data and clock supplied.
Control of turning on and off. As shown in the figure, one LED driving device 21 is a group of LEs of a predetermined number.
A plurality of such LED driving devices 21 are arranged in a line along the arrangement of the LEDs 7 in the printing device 20 as a whole by controlling the D7. FIG. 2 shows an example of the configuration of such an LED driving device 21. In FIG. 2, the same components as those in FIG. 7 are designated by the same reference numerals, and the description thereof will be omitted. It should be noted that the cycle of the clock signal supplied to the counter 12 may be equal intervals or unequal intervals, and preferably unequal intervals, as described below.

The output side of the latch circuit 2 for processing 4-bit data and the output side of the counter 12 are connected to the comparison circuit 11. The comparison circuit 11 determines the magnitude relationship between the data sent by the counter 12 (hereinafter referred to as data A) and the data sent by the latch circuit 2 (hereinafter referred to as data B) from data A to data B. Comparison is performed by subtraction, and a signal corresponding to the comparison result is transmitted. A concrete circuit configuration of the comparison circuit 11 is shown in FIG. 3, and Q3 to Q0 and D3 to D0 are the same as those shown in FIG. Also, the comparison circuit 1
The circuit configuration of 1 is a well-known configuration including an inverter, an AND circuit, and an OR circuit, and thus the description thereof will be omitted. On the output side of the comparison circuit 11, the source is connected to the power supply, and the drain is connected to the anode of the LED 7 through the connection pad P.
It is connected to the gate of the channel MOS transistor 6. The cathode side of each LED 7 is connected to a common ground line.

The LED driving device 21 thus constructed
The operation of the above will be described below. The shift register 1, the latch circuit 2, and the counter 12 perform the same operation as the conventional LED driving device shown in FIG. When the result of subtracting the data B transmitted by the latch circuit 2 from the data A transmitted by the counter 12 is positive, that is, AB> 0, the comparison circuit 11 outputs the output data of, for example, 0 to the MOS transistor 6 Sent to the gate of
The MOS transistor 6 is turned on. When the transistor 6 is turned on, a current flows from the power supply to the LED 7 and the LED 7 lights up. Conversely, data A to data B
When the result of subtracting is negative or 0, that is, A−B ≦
When it is 0, the comparison circuit 11 sends the output data of 1, for example, to the gate of the MOS transistor 6 to turn off the MOS transistor 6. By turning off the transistor 6, the current to the LED 7 is cut off and the LED 7 is turned off.

Specifically, the operation of turning on and off the LED 7 will be described with reference to the values of the data A and the data B. For example, if the data B is 0, only the LED is output when the data A is 0.
7 is off, and when the data A is 1 to 15, the value of (data A)-(data B) becomes positive, so L
ED7 is turned on. Also, for example, if the data B is 7 and the data A is 0 to 7, (data A)-
Since the value of (data B) is negative, the LED 7 is in the off state, and when the data A is 8 to 15, (data A)
Since the value of- (data B) becomes positive, the LED 7 is turned on. Further, for example, if the data B is 15, the value of (data A) − (data B) becomes negative regardless of the value of the data A, so that the LED 7 remains in the off state.

Since the ON / OFF control of the LED 7 is performed only by the comparison result of the comparison circuit 11 as described above by using the comparison circuit 11 performing such operation, the clock pulse signal supplied to the counter 12 is used. The periods need not be evenly spaced, and by supplying the counter 12 with clock signals having unequal pulse periods, it is possible to control the increase or decrease of the lighting time of the LED 7 based on the period of the clock signal. More specifically, due to the relationship with the γ characteristic described above, the period of the clock signal supplied to the counter 12 is shortened and the counting operation of the counter 12 is speeded up in the portion where the gradation is low, such as the gradations 1 and 2, to make the LED 7 faster. On / off of the LED 7 is finely controlled, while the period of the clock signal supplied to the counter 12 is lengthened and the counting operation of the counter 12 is delayed to increase the lighting / extinguishing time of the LED 7 in a portion having a high gradation of 8 or more. Control to be longer. In this way, the length of the lighting time of the LED 7 can be controlled by the cycle of the clock signal supplied to the counter 12. Therefore, it is possible to adjust the lighting time of the LED 7 in accordance with the γ characteristic without reducing the number of gradations.

The LED drive circuit in this embodiment is
Since the ON / OFF control of the LED 7 is performed only on the basis of the comparison result, a clock signal of a non-equidistant cycle is supplied to the counter to control the turning on / off of the LED 7, as shown in FIG.
Unlike the conventional LED driving device, it is not necessary to provide the flip-flop circuit 10, and naturally, a circuit for a set signal supplied to the flip-flop circuit 10 is also unnecessary. The circuit scale of the comparison circuit 11 is smaller than that of the flip-flop circuit 10 and the circuit related to the set / reset signal. Therefore, in an LED drive device that supplies a clock signal with a non-equidistant period to a counter and controls the turning on and off of the LED by the clock signal, the circuit scale can be reduced by about 20% compared to the conventional device. For example, in the A0 size LED drive circuit, the number of flip-flop circuits can be reduced by 15,000.

Further, as described above, since the control of turning on and off the LED 7 is performed by the comparison result data of the comparison circuit 11, the increase / decrease direction of the count value sent from the counter 12 is not a problem, and therefore the counter 12 does not have a problem. The type does not matter. That is, the counter 12 may be an up counter, a down counter, or an up / down counter. In this way, the counter 12
The following effects can be obtained regardless of the type. For example, when the counter 12 is composed of an up-counter, it is similar to the conventional LED driving device, and as shown in FIG. 4 (a), LEDa or LEDa is supplied by the clock signal of the non-equidistant cycle supplied to the up-counter. LEDg is turned on at the same time and turned off sequentially in accordance with the clock signal, as shown in FIG.
As shown in 1, the toner can be attached to the photosensitive drum. Incidentally, the number of LEDs is not limited to the above seven of a to g. Next, when the counter 12 is composed of a down counter, as shown in FIG. 5A, the LEDs 7 are sequentially turned on and turned off at the same time in accordance with the lighting control to attach toner to the photosensitive drum. You can Incidentally, FIG.
The illustration method of (a) and (b) is the same as the illustration method described in FIG.

Further, when the counter 12 is composed of an up / down counter, as shown in FIG. 4 (b),
A clock signal is supplied to the up-down counter, and the counter first performs a down-counting operation to sequentially lighten the LEDs from LEDg to LEDa. For example,
In the driving device of LEDg, the count value decreases sequentially from 15,
When it becomes 7, a signal of 0 is transmitted from the comparison circuit 11 and L
The EDg is turned on, and when the count value reaches 6 in the LEDf driving device, a signal of 0 is sent from the comparison circuit 11 and LEDf
Is lit up, and then LEDa is lit up in sequence.

Next, the counter performs an up-counting operation and controls to turn off the LEDs from LEDa to LEDg in the reverse order of lighting. For example, in the driving device of LEDa, when the count value becomes 1, the signal of 1 is transmitted from the comparison circuit 11 to turn off the LEDa, and in the driving device of LEDb, when the count value becomes 2, the signal of 1 from the comparison circuit 11 is sent. The sent LEDb is turned off, and then the LEDs g are turned off sequentially.

When the up / down counter is used in this way, as shown in FIG. 5 (b), the range of toner adhering to the rotating drum at each LED 7 is targeted to the center line 13 as if it were. It can be arranged. Therefore, the centers of the dots forming the print character can be made to coincide with each other, and thus the print quality can be improved.

In order to control the lighting time of each LED as shown in FIG. 4B, the up / down counter for 4-bit data cannot process, and for example, the up / down counter for 5-bit data is required. Become. When the above operation is performed with the 4-bit data up / down counter, the timing chart showing the lighting time of each LED is as shown in FIG. 4 (c), and as shown in FIG. 4 (b), Although it is not symmetrically left and right with respect to a line, it is almost symmetrical with respect to the center line, and in comparison with the conventional LED drive device, it is not possible to perform printing on the left and right sides with respect to the center line. The LED driving device can improve print quality even if the number of bits of processed data is 4 bits.

As described above, in the LED driving apparatus of the present embodiment, (1) the lighting time of the LED 7 can be controlled by the clock signal of the non-equidistant cycle supplied to the counter 12, (2) the non-equidistant interval. In the LED driving device of the type in which the clock signal of the cycle is supplied to the counter, the circuit scale of the entire printing device can be significantly reduced as compared with the conventional one. (3) Regardless of the type of the counter, the up-down When the counter is used, there is a remarkable effect that the print quality can be improved.

In the above description, the number of bits of data processed by the LED drive circuit device is 4 bits, but it is not limited to this.

[0028]

As described in detail above, according to the present invention, the counting means counts the supplied clock signal and sends the count value to the comparison circuit, and the comparison circuit outputs the count value sent by the counting means. And the data sent from the storage means are compared, and the switch means controls ON / OFF of the LED based on the comparison result data sent from the comparison circuit.
The on / off control of the LED can be controlled according to the cycle of the clock signal supplied to the counting means. Further, according to the present invention, since the operation of the switch means for controlling the ON / OFF of the LED is directly controlled by the output data of the comparison circuit, the conventional LED drive circuit does not require an auxiliary circuit for controlling the switch means. The circuit scale of the entire circuit can be reduced as compared with the circuit device. Further, according to the present invention, the counting operation in the counting means may be performed in any of the increasing, decreasing, increasing and decreasing directions. Therefore, it is possible to improve the print quality by arbitrarily setting the lighting and extinguishing timings of the LEDs.

[Brief description of drawings]

FIG. 1 is a block diagram showing an overall configuration of a printing apparatus including an LED drive circuit device of the present invention.

FIG. 2 is a block diagram showing the configuration of an embodiment of the LED drive circuit device of the present invention.

FIG. 3 is a logic circuit diagram showing an example of a configuration of a comparison circuit.

4A is a timing chart showing a lighting time of an LED when a down counter is used as the counter shown in FIG. (b) is a timing chart showing the lighting time of the LED when the up-down counter is used as the counter shown in FIG. 2. (c) is a timing chart showing the lighting time of the LED when an up-down counter is used as the counter shown in FIG. 2.

5A is a diagram showing a range of toner adhering to the photosensitive drum when a down counter is used as the counter shown in FIG. FIG. 3B is a diagram showing a range of toner adhering to the photosensitive drum when a down counter is used as the counter shown in FIG.

FIG. 6 is a graph showing a γ characteristic.

FIG. 7 is a block diagram showing a circuit configuration in a conventional LED drive circuit device.

FIG. 8 is a block diagram showing a circuit configuration in a conventional LED drive circuit device.

9 is a timing chart for explaining the operation of the LED drive circuit device shown in FIG.

10 is a timing chart for explaining an inconvenience when a clock signal having a non-equidistant cycle is supplied to the LED drive circuit device shown in FIG.

FIG. 11 is a diagram showing a range of toner attached to a photosensitive drum when a conventional LED drive circuit device is used.

[Explanation of symbols]

 11 ... Comparison circuit, 12 ... Counter.

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[Procedure amendment]

[Submission date] June 16, 1993

[Procedure Amendment 1]

[Document name to be corrected] Drawing

[Name of item to be corrected] Fig. 4

[Correction method] Change

[Correction content]

[Figure 4]

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI Technical indication H04N 1/036 A 9070-5C

Claims (3)

[Claims] 1. A storage unit for storing data for controlling lighting and extinguishing of a light emitting element and a control of a lighting time, a counting unit for performing a counting operation with a clock signal supplied, and data sent by the counting unit. And a comparison circuit for performing a magnitude comparison between the data sent by the storage means and the data sent by the storage means, and a switch means for controlling lighting and extinguishing of the light emitting element based on an output signal of the comparison circuit. LED drive circuit device with adjustment control. 2. The LED drive circuit device with gradation control according to claim 1, wherein the clock signals supplied to the counting means have unequal intervals. 3. The LED drive circuit device with gradation control according to claim 1, wherein the counting means is an up counter, a down counter, or an up / down counter.