KR950013390B1 - Auto control circuit of optical power - Google Patents

Abstract

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Description

Light output automatic control circuit

1 is a circuit diagram showing an example of a conventional optical output circuit.

2 is a circuit diagram showing a light output automatic control circuit according to the present invention.

* Explanation of symbols for main parts of the drawings

A20: comparator LD20: light emitting diode (light emitting device)

PT20: light receiving element Vref: reference voltage

Q20, Q22: first and second transistors.

The present invention relates to a light output automatic control circuit, and more particularly, data reading is applied to an optical pickup device to automatically control an output light amount of a laser diode emitting a light beam for reading information from an optical disk of an information recording medium. It relates to a light output automatic control circuit.

In general, a hard disk drive or a laser disk drive applied as a large-scale information recording apparatus employs an optical pickup device equipped with a laser light emitting means for generating a light beam, and irradiates the light beam generated by the laser light emitting means toward the disk. The reflected light reflected from the disk is post-processed to perform data reproduction.

FIG. 1 is a circuit diagram showing an exemplary configuration of an optical output circuit for generating such a light beam, and includes a first transistor Q1 switched by an optical beam generation signal applied through a resistor R1, and the first transistor. A second transistor Q2 having a base connected to the collector of Q1 and a collector connected to the power supply Vcc, a third transistor Q3 having a base connected to the emitter of the second transistor Q2, and The light emitting diode LD as a light emitting element connected between the collector of the third transistor Q3 and the power supply Vcc is provided.

In the conventional optical output circuit having such a configuration, when the light beam generation signal is applied to the base of the first transistor Q1 via the resistor R1, the first transistor Q1 is switched on according to the light beam generation signal. Since the second and third transistors Q2 and Q3 are switched off / on accordingly, the light emitting diode LD generates an optical beam and outputs the light beam toward the optical disk.

However, since the optical output circuit shown in FIG. 1 has a constant optical output output from the light emitting diode LD regardless of the position characteristic of the disk where the light beam reaches, precisely the information recording surface, the light output diode LD The light level incident on the light receiving element differs depending on the distance or position to the disc, i.e., the information recording surface of the disc.

Therefore, when the reflected light differs depending on the distance or position between the light emitting diode LD and the disk, a malfunction of the device or an error in the read signal occurs, and regardless of the position and distance of the information recording surface of the disk. There is a disadvantage that the power loss is increased because it always outputs a constant light.

The present invention is to solve the above-mentioned problems in the prior art, the light beam emitted from the light emitting diode to automatically adjust the light output according to the size of the light reflected to the light receiving element via the reflective surface of the disk on which the information is recorded The purpose is to provide an output automatic control circuit.

In order to achieve the above object, according to the present invention, one end is connected to a first transistor that is biased by a bias resistor with respect to an input voltage to drive a light emitting element, and a light receiving element that receives light beams reflected from the light emitting element. And a comparison means for comparing the outputs of the light receiving elements with reference voltages set at different stages, and a base bias formed by the output of the comparison means to control the base driving current of the first transistor. A control circuit is provided.

According to the photocurrent automatic control circuit according to the present invention having the above-described configuration, the reflected light of the light beam emitted from the light emitting element is detected by the light receiving element and then compared with the reference voltage in the comparison means, and the comparison output is the base bias voltage of the second transistor. Is applied to control the base driving current of the first transistor so that the light output of the light emitting device is automatically controlled.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

2 is a view showing an optical output automatic control circuit according to the present invention, in which light is emitted as a light emitting element on the collector side of a first transistor Q20 having a base bias formed by a bias resistor R20 with respect to an input voltage Vcc. The diode LD20 is connected, and the input level of the non-inverting terminal + is adjusted by the voltage divider R22 and R23 on the output side of the light receiving element PT20 that receives the reflected light of the light beam from the light emitting diode LD20. In addition, a comparator A20 as a comparison means having a reference voltage Vref set to the inverting terminal (−) is connected.

The base of the second transistor Q22 is connected to the output side of the comparator A20 via a resistor R23, and the second transistor Q22 has a current according to the light reception level compared and output from the comparator A20. It is driven to adjust the base bias of the first transistor Q20, so that the light output of the light emitting diode LD20 is automatically controlled.

Next, the operation of the light output automatic control circuit according to the present invention configured as described above will be described.

First, when an input voltage Vcc is applied to the base of the first transistor Q20 where the base bias is formed by the resistor R20, it is connected between the input voltage Vcc and the collector of the first transistor Q20. The light emitting diode LD20 emits light. When the light beam from the light emitting diode LD20 is reflected on the reflecting surface (i.e., the information recording surface of the disk), the reflected light is received by the light receiving element PT20 and leveled by the resistors R22 and R23. A20) is applied to the non-inverting terminal (+).

Therefore, the comparator A20 compares the light receiving level of the light receiving device PT20 based on the reference voltage Vref set at the inverting terminal (−), and the output level is increased according to the size of the light receiving level of the light receiving device PT20. And the output thereof is applied from the comparator A20 to the base of the second transistor Q22 via the resistor R24. That is, when the amount of light received by the light receiving element PT20 is large, since the output of the comparator A20 becomes high level, the transistor Q22 is turned on, and according to the conduction of the transistor Q22, the base current of the transistor Q20 is turned on. Since is reduced, the light emission output from the light emitting diode LD is reduced.

On the other hand, if the light receiving level output from the light receiving element PT20 is lower than the reference voltage Vref set in the inverting terminal + of the comparator A20, the output of the comparator A20 is at a low level, and accordingly the transistor Since Q22 is in a non-conductive state, the light emission output from the light emitting diode LD20 is increased by the conduction of only the transistor Q20. Therefore, in the light emitting diode LD20, the light emission output level may be constantly maintained based on the level of the reflected light, that is, the light receiving level by the light receiving element PT20.

As described above, according to the light output automatic control circuit according to the present invention, since a constant level of light output is always obtained from the light emitting diode according to the position and distance of the reflecting surface, the light emitting diode is provided adjacent to the reflecting surface of the disk, for example. Even if the light output level is automatically reduced, the malfunction of the light receiving element due to excessive incident light is reduced and power loss is reduced.

In addition, according to the present invention, if the integrated circuit (IC) of the circuit configuration for automatic control of the light emission output level can be reduced, the area occupied on the PCB can be reduced, thereby contributing to the miniaturization of the device or device.

Claims (1)

The base bias is set by the bias resistor R20 with respect to the input voltage, thereby driving the first transistor Q20 for driving the light emitting device LD20 and the light receiving element PT20 for receiving the reflected light of the light beam from the light emitting device LD20. ) Is connected to one end and a comparison means A20 for comparing the output of the light receiving element PT20 by the reference voltage Vref set at the other end, and a base bias is formed by the output of the comparing means A20. And a second transistor (Q22) for controlling the base driving current of the first transistor (Q20) so that the light output level of the light emitting element (LD20) is constantly controlled.