JPS63253973A - Light emission diode driving system - Google Patents

Abstract

PURPOSE:To vary the printing density without deteriorating the printing quality, by bringing a light emission diode to constant-current driving by plural transistors, and varying its light quantity. CONSTITUTION:Current limiting resistors 4-6 are connected to collectors of three pieces of transistors 1-3, these transistors 1-3 are connected in parallel to a power source Vcc, a light emission diode 7a is connected to emitters of the transistors 1-3 which are connected in parallel, and by the sum of currents from the transistors 1-3, the light emission diode 7a is brought to constant- current driving. Subsequently, the current flowing to the light emission diode 7a through each of the transistors 1-3 is limited, and an ON/OFF control of each of the transistors 1-3 is executed. In such a way, the printing density can be corrected without causing the deterioration of the printing quality, such as fog, etc.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention relates to an electrophotographic printer equipped with a group of light emitting diodes that irradiate the surface of a photoreceptor with light and form an electrostatic latent image on the surface, particularly an electrophotographic printer that emits light. This relates to a method of driving a diode.

[Conventional technology]

Conventionally, in this type of printer, in order to correct print density due to variations in photoreceptor sensitivity, changes in environmental conditions, etc., density correction has been performed by adjusting the potential applied to the developer, that is, the development bias.

[Problem that the invention seeks to solve]

However, when the density is corrected by adjusting the developing bias as described above, fogging or the like occurs at the same time as the density is changed, resulting in a deterioration in print quality.

SUMMARY OF THE INVENTION An object of the present invention is to provide a light emitting diode driving method that eliminates the above-mentioned problems.

[Means for solving problems]

The present invention provides an electrophotographic printer equipped with a group of light emitting diodes that irradiates the surface of a photoreceptor with light to form an electrostatic latent image on the surface, in which each light emitting diode included in the group of light emitting diodes is a plurality of parallel-connected transistors that drive the LED at a constant current, a resistor that limits the current flowing to the light emitting diode through each of the transistors, and a control unit that controls ON and OFF of each of the transistors. This is a light emitting diode drive system characterized by:

〔Example〕

Hereinafter, one embodiment of the present invention will be described with reference to the drawings.

In FIG. 1, the light emitting diode group installed in the electrophotographic printer according to the present invention includes a plurality of light emitting diodes arranged in a row in the width direction of the photoreceptor (the path shown in the figure),
In the figure, the circuit is shown as a circuit that drives the n-th light emitting diode 7a. It goes without saying that the first to n-1th light emitting diodes 7b are individually driven by a drive circuit having the same configuration as the drive circuit shown in FIG.

In this embodiment, current limiting resistors 4, 5.6 are connected to the collectors of three transistors 1, 2.3, and these transistors 1, 2, 3 are connected in parallel to the power supply Vce. A light emitting diode 7a is connected to the emitters of the transistors 1, 2.3, and the light emitting diode 7a is driven by the sum of currents from the transistors 1, 2.3.

At the bases of the transistors 2, 3, there is a gate circuit 8. for driving each of the transistors 2.3. The gate circuit 9 is connected to one input terminal of the gate circuit 8 and the gate circuit 9. A buffer circuit 10 opens the gate circuit 8 when the concentration is 1M', and a buffer circuit opens the gate circuit 9 when the concentration is 1H'. 11 respectively. Further, a shift register 12 for storing information printed on the n-th light emitting diode 7a is connected to the base of the transistor 1 and also connected to the other input terminals of the gate circuits 8 and 9. Here, the gate circuit 8,
9゜13, buffer circuit to, tt, shift register 12 turns transistors 1, 2.3 on and off
A control section that performs F control is configured.

In the embodiment, it is assumed that data to drive the n-th light emitting diode 7a is stored in the shift register 12 and drives the n-th light emitting diode control section through the gate circuit 13 at a certain timing. .

If the concentration is at a low level, the output from the shift register 12 is input to the transistor 1. On the other hand, since there are no output signals from the buffer circuits to and tt, the gate circuit 8. Gate circuit 9 remains closed and therefore
The light emitting diode 7a allows the minimum current to flow through the resistor 4, and the light emitting diode 7a irradiates the surface of the photoreceptor with the minimum amount of light. Therefore, the surface potential of the photoreceptor is minimized, and the amount of toner adhering to the electrostatic latent image on the photoreceptor is small, resulting in a low density.

If a higher density print output is required, input a high level M signal to the buffer circuit IO.
A signal from the shift register 12 is input to the transistor 2 via the gate circuit 8. At this time.

The sum of the currents from the two transistors 1 and 2, which is limited by the resistors 4 and 5, flows to the light emitting diode 7a, the amount of light from the light emitting diode 7a increases, and printing with higher density is performed.

If even higher density printing is required, the buffer circuit 11
A high level H signal is input to the transistor 3, and a signal from the shift register 12 is input to the transistor 3 via the gate circuit 9. At this time, resistors 4 and 5 are connected to the light emitting diode 7a.
．． The sum of the currents from the three transistors 1, 2.3 limited by 6 flows, and printing with maximum density is performed.

〔Effect of the invention〕

As explained above, by driving a light emitting diode with a constant current using multiple transistors and changing the amount of light,
This has the effect of being able to change print density without causing deterioration in print quality such as fogging.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing one embodiment of the present invention.

Claims (1)

[Claims] (1) In an electrophotographic printer equipped with a group of light emitting diodes that irradiate light onto the surface of a photoreceptor and form an electrostatic latent image on the surface, each light emitting diode included in the group of light emitting diodes is A plurality of parallel-connected transistors that drive the LED at a constant current, a resistor that limits the current flowing to the light emitting diode through each of the transistors, and a control unit that controls ON and OFF of each of the transistors. A light emitting diode drive system featuring