JPH01102980A - Semiconductor laser controller - Google Patents

Abstract

PURPOSE:To accurately maintain an emission light intensity constant by varying a drive current and a drive current range in response to the temperature characteristic of a semiconductor laser light emitting element. CONSTITUTION:When an emission light intensity is reduced to a drive current Id, it is detected by a photodiode PD, an I/V converter 5 and a comparator 6, and data Dc counted up from reference data is supplied to a D/A converter 2. Thus, since an output current IR decreases, the base potential of a transistor Tr is reduced, the current Id is increased, and a reference emission light intensity is maintained. On the other hand, when the emission light intensity is increased to the current Id, the output current IR is increased. Accordingly, the base potential of the transistor Tr is raised, the current Id is decreased, and the reference emission light intensity is maintained.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a semiconductor laser control device, and more particularly, a semiconductor laser control device that controls the emission intensity of a semiconductor laser element so as to always maintain it constant without depending on the ambient temperature. Regarding.

(Prior Art) Conventionally, a semiconductor laser control device has basically had the configuration shown in FIG. The device includes a voltage/current converter (V/I converter) for generating a constant drive current I;
A modulation circuit is provided that controls the supply of the drive current 1d to the semiconductor laser element LD to cause it to emit or not emit light.

For example, the V/I converter uses the reference voltage source V r @f in the same figure.
The modulation circuit is connected in parallel between both ends of the semiconductor laser element LD, and is set to either high or low depending on the logic level of the video signal Svo. The transistor Q2 and the like control the supply of the drive current (2) to the semiconductor laser element LD by changing its impedance. That is, the light emission intensity of the semiconductor laser device LD is always kept at 7 constant, and the light emission amount of the semiconductor laser device LD (corresponding to the product of the light emission intensity and the light emission time ) to control the desired number of quantization steps.

(Problems to be Solved by the Invention) However, the semiconductor laser device LD has temperature dependence, and as shown in FIG. Since the rate of change in the light emission intensity (current to start) and the change in the drive current (referred to as the I/L characteristic) varies greatly depending on the ambient temperature T4, the light emission intensity should always be set to a constant value regardless of the temperature. It has been extremely difficult to obtain high-precision resolution.

To explain the problem more concretely based on the figure, when the ambient temperature T is 0°C, the drive current 2, emits light at approximately 40 mA (corresponding to the threshold value ITH) to 55 mA, and when the ambient temperature T, At 25°C, drive current ■.

emits light at approximately 50mA to 70mA, and the ambient temperature T
When 2 is 50℃, the drive current I is about 60mA to 85mA.
Light is emitted at A. Therefore, even if the drive current (■) at a specific ambient temperature T6 is set in advance, the threshold value (7) and the slope of the I/L characteristic curve will vary depending on the temperature.
There is variation in the precision of optical output control at high and low temperatures, and problems such as color unevenness and the inability to obtain the desired gradation occur in so-called facsimile machines and printers that reproduce images using semiconductor lasers as light sources. arise.

(Means for Solving the Problems) The present invention has been made in view of the above problems, and it is possible to reduce temperature dependence and obtain light emission characteristics with high precision and excellent linearity. The purpose of the present invention is to provide a semiconductor laser control device.

To achieve this object, the present invention provides a semiconductor laser control device comprising a semiconductor laser light emitting element and a current supply means for supplying a drive current to the semiconductor laser light emitting element, wherein the current supply means a light detection means for detecting the light emission intensity of the element; a control means for detecting an error between the output signal of the detection means and a set reference signal and increasing or decreasing the drive current so as to bring the error closer to zero; and an ambient temperature. and a temperature compensation means for detecting the error value and changing the error value at a predetermined ratio in accordance with temperature changes. By compensating, the emission intensity of the semiconductor laser light emitting element is always kept constant with high precision.

(Example) Hereinafter, an example of a semiconductor laser control device according to the present invention will be described based on FIG.

First, to explain the configuration, in FIG. 1, LD is a semiconductor laser light emitting device, and PD is a semiconductor laser light emitting device.・It is a diode.

T is a pnp transistor whose emitter is connected to the power supply VCC via a resistor R1, and whose collector is connected to the anode of the semiconductor laser light emitting device LD.

1 is a differential amplifier, which has an output terminal connected to the base of the transistor Tr via a resistor R2 and an inverting input terminal via a feedback resistor R3, and a non-inverting input terminal connected to a power supply VCC and a ground contact. A thermistor element Th+ having a negative temperature characteristic is connected in parallel to both ends of the resistor R3.

2 is a D/A converter, which has an output terminal connected to the inverting input terminal of the differential amplifier 1, and a setting terminal RBF and a power supply V for setting the variable range (span) of the output current Ii. A resistor R6 and a thermistor element Th2 having negative temperature characteristics are connected in parallel with each other.

Then, control data D from the fine adjustment control circuit 7, which will be described later.
, by adjusting the output current I, and setting the base potential of the transistor T, finely adjusting the drive current I to the semiconductor laser light emitting device LD.

3 is a NOR circuit, which receives the video signal svn and the synchronization signal S.

will be supplied. Here, the video signal svn consists of a rectangular signal with a time width corresponding to the quantization step. For example, when the number of quantization steps is 256 (=28), 256
This results in rectangular signals with different time widths.

4 is a modulation circuit, and the signal from NOR circuit 3 is “L”
level, the output becomes high impedance and the drive current I from the transistor T is transferred to the semiconductor laser light emitting element L.
When the signal from the NOR circuit 3 is at the "H" level, the output becomes low impedance and the drive current Id is sucked, thereby supplying the drive current I to the semiconductor laser light emitting element LD. During this period, the semiconductor laser light emitting device LD is in a non-emitting state.

5 is a current/voltage converter (1/V converter), and the current output from the photodiode PD.

is converted into V voltages that are inversely proportional to it. That is, when the current decreases, the voltage VW increases in inverse proportion to it, and conversely, when the current increases, the voltage V increases.

decreases.

6 is a comparator, which compares the set reference voltage V REF and I/V
The output voltage V of the converter 5 is compared with the voltage V.

Comparison signals S and H are output, which are at the "H'" level when the voltage is less than the reference voltage VREF, and which are at the "L" level when vice versa.

That is, the output voltage V output from the I/V converter 5 when light is emitted with the reference voltage V□ and the drive current ■ at a specific ambient temperature T.

Therefore, this temperature and drive current are set as the reference conditions.

7 is a fine adjustment control circuit which includes a microprocessor and the like. This is the synchronization signal S. When the comparison signal STH input in synchronization with K is at the "H" level, 8-bit digital data D is stored in the internal register. is counted down by 1, and in the opposite case is counted up by 1, and the digital data Do is sent to D/D in synchronization with the synchronization signal ScK.
Supplied to A converter 2. That is, the reference data D indicates when the above reference conditions are met. is stored in an internal register in advance,
When the comparison signal STH from the fine adjustment control circuit 7 is at “H” level, the data DC is counted down by 1 and the D/A
By supplying the converter 2, the semiconductor laser light emitting device L
The emission intensity of D is suppressed, while the semiconductor laser light emitting device L
When the light emission intensity of D decreases below the set value, the comparison signal STI+ from the comparator 6 becomes "L" level, so in order to prevent this decrease, the digital data Dc counted up by 1 is sent to the D/A converter 2. supply

Next, the operation of this embodiment will be explained.

When the emission intensity decreases with respect to the drive current I, this decrease in emission intensity is caused by the photodiode PD.

The data Dc detected by the I/V converter 5 and the comparator 6 and counted up from the reference data is
It is supplied to the A converter 2. As a result, the output current It decreases, so the base potential of the transistor T decreases,
The drive current I increases to maintain the reference light emission intensity.

On the other hand, when the emission intensity increases with respect to the drive current Id, this increase in emission intensity is detected by the photodiode PD, the I/V converter 5, and the comparator 6, and the data is counted down from the reference data. Dc is supplied to the D/A converter 2. As a result, the output current T increases, the base potential of the transistor T increases, the drive current I decreases, and the reference light emission intensity is maintained.

Here, the semiconductor laser light emitting device LD has temperature dependence as shown in FIG. 2, but when the thermistor element Thl detects a rise in temperature, the resistor R3
Since the parallel resistance value of is decreased and the potential of the non-inverting input terminal P of the differential amplifier l is lowered, the threshold value rto of the drive current to the semiconductor laser element LD is moved to the right side in FIG. Conversely, when the temperature decreases, the parallel resistance value of resistor R3 and thermistor element T'h+ increases, the potential of non-inverting input terminal P of differential amplifier 1 rises, and semiconductor laser light emitting element LD
This results in moving the threshold value ITH of the drive current to the left side in FIG.

On the other hand, when the thermistor element Th□ detects a rise in temperature, the parallel resistance value of the resistor R6 and thermistor element Th□ decreases, and the current flowing into the terminal REF of the D/A converter 2 increases, so that the output current ■ is variable. Conversely, when the temperature decreases, the parallel resistance value of the resistor R6 and thermistor element Th□ increases, and the current flowing into the terminal REF of the D/A converter 2 decreases, so the variable range of the output current IR is increased. Narrow down. That is, the thermistor element Th2 is the semiconductor laser light emitting element LD.
The variable range of the output current is set according to the power/L characteristics.

In this way, the thermistor elements Th, , Th2 control the driving current (2) according to the temperature characteristics of the semiconductor laser light emitting device LD shown in FIG. When the temperature T is 0°C, the range X1 is approximately 40 mA to 55 mA, and when the ambient temperature T is 25°C, the range X2 is approximately 50 mA to 70 mA.
When , is 50℃, the range X is approximately 6QmA to 85mA,
It is possible to keep the luminescence intensity constant even when the temperature changes.

FIG. 3 is a block diagram showing another embodiment, and the difference from the embodiment shown in FIG. 1 is that the thermistor element Th3. The point is that Th4 is used. That is, the thermistor element Th3 corresponds to the thermistor element Thl in FIG. 1, and lowers the potential of the non-inverting input terminal P of the differential amplifier 1 as the temperature rises, and the thermistor element Th4 corresponds to the thermistor element Thl in FIG. By lowering the amplification factor of the differential amplifier 1 as the temperature rises, the drive current I is controlled according to the characteristics shown in FIG. 2, and the emission intensity is maintained constant.

(Effects of the Invention) As explained above, according to the present invention, the drive current and drive current range are changed according to the temperature characteristics of the semiconductor laser light emitting device, so that the light emission intensity is always kept constant with high precision. This makes it possible to provide an excellent light source for image forming apparatuses and the like.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing one embodiment of a semiconductor laser control device according to the present invention, FIG. 2 is a characteristic curve diagram for explaining the operation of this embodiment, and FIG. 3 is a block diagram showing another embodiment of the present invention. 4 is a circuit diagram showing a conventional example, and FIG. 5 is a characteristic curve diagram showing temperature dependence of a semiconductor laser element. 1: Differential amplifier 2: D/A converter 3: NOR circuit 4: Modulation circuit 5: I/V converter 6: Comparator 7: Fine adjustment control circuit LD: Semiconductor laser light emitting device PD: Photo diode T, :pnp) transistors Thl, Th2. Th3. Th4: Thermistor element VREF: Reference voltage

Claims (2)

[Claims] (1) In a semiconductor laser control device having a semiconductor laser light emitting element and a current supply means for supplying a driving current to the semiconductor laser light emitting element, the current supply means is configured to provide a light source for detecting the emission intensity of the semiconductor laser light emitting element. a detection means, a control means for detecting an error between the output signal of the detection means and a set reference signal, and increasing or decreasing the drive current so as to bring the error closer to zero; and temperature compensation means for changing the error value at a predetermined ratio. (2) The temperature compensating means has a thermistor having negative or positive temperature characteristics, and by changing the error value according to a change in the output of the thermistor, the drive current is adjusted at a predetermined ratio as the temperature rises. The semiconductor laser control device according to claim 1, wherein the semiconductor laser control device increases the number of semiconductor lasers.