JPH03183175A - Light quantity regulator - Google Patents

Abstract

PURPOSE:To perform a multilevel printing by regulating the power of light with time by utilizing a pulse width modulating system. CONSTITUTION:A triangular wave and a DC voltage are inputted to the positive and negative input terminals of a comparator 8, respectively. A square wave is outputted from the comparator 8 and the pulse width of an output is changed by the voltage of the negative input terminal. Therefore, a period during which an LED is turned on is changed. A printing power for a prescribed period is represented by the product of the light quantity of the LED and the time for which the LED is turned on and changed by the pulse width because the light quantity of the LED is constant. Since voltage is controlled, a control can be relatively simply performed with an excellent accuracy and, when the frequency of the triangular wave is high, the number of pulses during a prescribed time (a printing time) is high, a multilevel printing being facilitated.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an LED printer in which the amount of light from an LED can be changed relatively easily and accurately in order to enable gradation printing.

[Conventional technology]

FIG. 3 is a schematic diagram showing a conventional device, and in the figure (1
) is an LED (light emitting diode), (2) is a current limiting resistor, (8) is a P-channel MO8 transistor, (
4) is an analog switch, (6) is a reference voltage input,
(6) is an operational amplifier, (γ) is a decoder, and (8) is a power supply.

Next, the operation will be explained. A constant current source is created by the operational amplifier (6) and the transistor (8), and this current drives the L E D (1) by >6°. By controlling the analog switch (4) connected to the gate of the transistor (8) by the decoder, the transistor is selected, the constant current value is adjusted by the resistance ratio, and the light intensity of the LED (1) is adjusted. ing.

Therefore, the density of the print is constant.

[Problem to be solved by the invention]

Conventional devices for adjusting the light intensity of LEDs are configured as described above, so the current value is constant, and even if transistors are used to create multiple gradations, there are problems such as the problem that it cannot be increased very much due to variations etc. was there.

This invention was made to solve the above-mentioned problems, and it is an object of the present invention to provide a light amount adjusting device that can relatively easily adjust the amount of light in multiple stages.

[Means to solve section Im]

The light amount adjusting device according to the present invention does not adjust the amount of light from an LED using a constant current, but uses PWM to adjust the power of the light depending on time, thereby enabling gradation printing.

[Effect]

The gradation printing according to this invention adjusts the period during which the LED is on, and if a certain period of time is maintained, it becomes equivalent to adjusting the amount of light from the LED with an electric current.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. 1st
In the figure, (1) is an LED, (2) is a resistor, (8) is a transistor, (4) and (8) are comparators, (9) is a triangular wave or sawtooth wave generator, (10 is a control voltage generator) It is a device.

Next, the operation will be explained. A triangular wave is input to the positive input terminal of the comparator (8), and a DC voltage is input to the negative input terminal. The output of the comparator is a square wave, but the pulse width of the output changes depending on the voltage at the negative input terminal, as shown in FIG. 3 (8).

Therefore, the period during which the LED is on will change.
If you look at a certain period of time, the printing power is expressed as the product of the light intensity of the LED and the time it is on, and since the light intensity of the LED is constant,
Varies depending on pulse width.

Since it is controlled by voltage, it can be controlled relatively easily and accurately, and if the frequency of the triangular wave is high, the number of pulses during a certain period (printing time) will be large, making it easy to print in multiple gradations.

By controlling a large number of devices shown in FIG. 1, it can be used as a printing device for an LED printer.

〔Effect of the invention〕

As described above, according to the present invention, the amount of light can be adjusted easily and with relatively high accuracy, making it easy to perform gradation printing using an LED printer.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing a light amount adjustment device for an LED printer according to an embodiment of the present invention, FIG. 2 is a waveform diagram showing the operation of an embodiment of this invention, and FIG. 3 is a conventional light amount adjustment device. FIG. (1) is LED, (2) is resistor, (8) is Pch MO
S transistor, (4) is analog switch, (6)
is a reference voltage input, (6) is an operational amplifier, (7) is a decoder, (8) is a power supply, (9) is a triangular wave generator, and αO is a control voltage generator. In the figures, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] A current-limiting resistor that is connected to a power supply and the other end connected to an LED (light emitting diode), an N-channel MOS transistor whose one end is grounded, and the other end connected to the other end of the LED, and an output. A light amount adjusting device comprising a comparator connected to the gate of the transistor, a triangular wave or sawtooth wave generating circuit connected to its positive input, and a control voltage generating circuit on its negative side.