JPH03281267A - Led driving circuit of led printer - Google Patents

Abstract

PURPOSE:To finely express the gradation of printing without increasing the number of LEDs by changing LED driving pulse width according to printing gradation data to change density in an one dot unit. CONSTITUTION:A printing gradation register 3 is a register holding printing gradation data and outputs the printing gradation data to a microprocessor 4. The microprocessor 4 sets the time driving an LED 12 to a timer 5 according to the printing gradation data. A drive circuit 6 outputs the time pulse set by the timer 5 to an AND circuit 8 to drive the LED 12. When the driving pulse width of the LED 12 is set to A, B, C, the luminous intensity of the LED changes to D, E, F. When the luminous intensity of the LED 12 changes, density also changes in proportion to the change of said luminous intensity and, therefore, gradation is carried out in three stages in this case by the setting of the pulse widths A, B, C. As mentioned above, by setting the time of a drive pulse to the timer 5 according to printing gradation data, gradation printing can be easily carried out.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an LED printer using an LED array as a light source.
This invention relates to an ED drive circuit.

[Prior Art] FIG. 3 is a circuit diagram of a conventional example of an LED drive circuit for an LED printer.

Power supply! There is a resistor 9 between Q7 and ground. NPN transistor 10. LEDs 12 are connected in series, and a capacitor 11 is connected between the power supply line 7 and ground. The print information register 1 is a shift register and holds the print information sent from the logic section 2. This print information register 1 consists of bits equal to the number of print digits, and each bit corresponds to each LE.
D, and print information "1" means "print".

In this case, the seventh bit from the top of the print information register 1 corresponds to LED 12. Drive circuit 5 is LED
When the printer's print switch (not shown) is pressed,
Outputs a pulse signal with a constant pulse width. If the pulse signal is sent from the drive circuit 5 and "1" is set in the upper 7th bit of the print information register 1, the AND circuit 8 outputs a "1" signal to turn on the transistor 10 and turn on the LED 12. light up.

[Means to be Solved by the Invention] The conventional LED printer described above controls the LED with a fixed pulse width and turns on the LED for a fixed period of time. Therefore, in order to delicately express the gradation of printing, it is necessary to increase the number of LEDs. The resolution can be increased by increasing the resolution, but this has its limits and the structure becomes complicated, so it has the disadvantage that it is not easy to express delicate gradations.

An object of the present invention is to provide an LED drive circuit for an LED printer that can delicately express the gradation of printing without increasing the number of LEDs.

[Means for Solving the Problems] The LED drive circuit of the LED printer of the present invention has the following features:
A print information register that holds print information on whether to turn on D, a print gradation information register that holds print gradation information of the relevant LED, a timer for each LED, and a time corresponding to the print gradation information. means for setting and activating the timer, and a drive unit that turns on the LED until the timer times out if print information for turning on the LED is held in a print information register. .

[Function] By changing the print gradation information set in the print gradation information register, the illuminance of the LED changes, and the LED
It is expressed subtly every time.

[Example] Next, an example of the present invention will be described with reference to the drawings.

FIG. 1 is a circuit diagram of an LED drive circuit of an LED printer according to an embodiment of the present invention.

This embodiment is constructed by adding a print gradation register 3, a microprocessor 4, and a timer 5 to the conventional example shown in FIG. The print gradation register 3 is a register that holds print gradation information, and the print gradation information is sent to the microprocessor 4.
Output to. The microprocessor 4 sets the time for driving the LED 12 in the timer 5 according to the print gradation information. The drive circuit 6 outputs a time pulse set by the timer 5 to the AND circuit 8. From then on, as before, L
ED 12 is driven.

In FIG. 2, the driving pulse widths of LE D 12 are A and B.

When set to C, it is shown that the illuminance of L E D 12 changes corresponding to E and F according to the set value. When the illuminance of L E D 12 changes, the density also changes proportionally, so in this case, the pulse widths A, B, C
The settings result in three-level gradation printing.

In this way, by setting the driving pulse time in the timer 5 according to the printing gradation information, gradation printing can be easily performed.

[Effects of the Invention] As explained above, the present invention provides LE
By changing the D drive pulse width and changing the density in units of one dot, it is possible to express subtle and clear gradations.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram of an LED drive circuit of an LED printer according to an embodiment of the present invention, and Fig. 2 shows the LED drive pulse width and LED.
FIG. 3 is a circuit diagram of an LED drive circuit of a conventional LED printer. 1...Print information register, 2...Logic section, 3...
Print gradation register, 4...Microprocessor, 5...Timer, 6...Drive circuit, 7...
・Power supply line, 8...AND circuit, 9...
Resistor, 10...NPN transistor,

Claims (1)

[Claims] 1. In an LED printer using an LED array as a light source, a print information register that holds print information indicating whether to turn on the LED, and a print gradation register that holds print gradation information of the LED. An information register, a timer for each LED, a means to set the time according to the print gradation information in the timer and start it, and if the print information to turn on the LED is held in the print information register. , a drive unit that turns on the LED until the timer times out.
D drive circuit.