JP2692629B2 - Light emitting element drive circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light emitting element drive circuit for driving a light emitting element such as a laser diode, and more particularly to a light emitting element drive circuit for driving a plurality of light emitting elements in parallel.

[0002]

2. Description of the Related Art As a circuit using a light emitting element such as a laser diode, there is an optical transmitter often used in the field of optical communication. Normally, one laser diode is used as the light source in an optical transmitter. However, when high optical power is required, the output light of the two laser diodes is polarized and combined to increase the intensity of the output light. In such a case, in order to prevent the size of the drive circuit for supplying the current to the laser diode from increasing, 1
Often, two laser diodes are operated in parallel by one driving circuit.

FIG. 4 shows a conventional light emitting device.
The outline of the configuration of the light-emitting element drive circuit that operates the
I gave it away. First and second light emitting element 11₁,
11 _TwoIs the corresponding analog switch 1
2₁, 12_TwoConnected to a power source (not shown)
You. In addition, the first and second light emitting elements 11₁, 11_TwoIs it
Each resistor 13₁, 13_TwoIs grounded through. Pa
The pulse generator 14 has a set constant duty ratio.
It is a circuit that outputs the loose signal 15. The pulse signal 15 is
Analog switch 12₁, 12_TwoTo control its continuity
Is input as a control signal.

FIG. 5 shows an example of a signal waveform output from the pulse generator shown in FIG. The pulse signal 15 output from the pulse generator 14 has a constant cycle, and the ratio of the pulse output period to the pulse non-output period in one cycle can be arbitrarily set.

Returning to FIG. 4, the description will be continued. The analog switches 12 ₁ and 12 ₂ are made conductive only while a pulse is being input. As a result, the corresponding light emitting elements 11 ₁ and 11 ₂ emit light only during this period. Therefore, the average optical output power of the light emitting elements 11 ₁ and 11 ₂ can be changed by the time during which the analog switches 12 ₁ and 12 ₂ are conducting, that is, the duty ratio of the pulse signal 15. Since the pulse signal 15 output from the pulse generator 14 is commonly applied to the _two analog switches 12 ₁ and 12 ₂ , their conduction times are the same,
If the characteristics of the two light emitting elements are the same, the average amount of current flowing through them becomes equal to each other.

A light emitting element drive circuit in which the conduction time of the switching element is controlled by the pulse width of the pulse generator as described above is also disclosed in Japanese Patent Application Laid-Open No. 1-223789. In this circuit, the switching element is controlled by pulse width modulation and the pulse width thereof is shortened to supply a small amount of current to the light emitting element even during idling.

[0007]

In the conventional circuit for controlling the conduction of the analog switch by the same pulse signal, if the characteristics of the two light emitting elements are the same, the average current amounts of the two light emitting elements are the same. However, in this circuit,
Since it is not possible to adjust the ratio of the currents flowing in the two light emitting elements, variations in the characteristics of the light emitting elements cause a difference in the amount of current flowing. The more current that flows, the faster the deterioration of the light emitting element. Therefore, the life of one of the two light emitting elements, which has the most current, becomes shorter than that of the other. As a result, there is a problem that the reliability of a device using a plurality of light emitting elements is reduced. Further, even if the characteristics of the light emitting elements are temporarily different from each other due to changes in ambient conditions such as temperature and humidity, the conventional circuit cannot correct the difference, resulting in a difference in element deterioration. There is a problem.

It is also possible to provide one pulse generator for one light emitting element and adjust the amount of current flowing individually to equalize the amount of current flowing through the two light emitting elements. However, in this case, there is a problem that two pulse generators are required and the circuit scale becomes large. Further, when the pulse generators are provided independently, there is a problem that the configuration of the control circuit for adjusting the current amount of each of the two light emitting elements while keeping the total light emission amount constant becomes complicated. is there.

SUMMARY OF THE INVENTION An object of the present invention is to provide a light emitting element drive circuit having a simple circuit configuration capable of keeping the amounts of currents flowing in a plurality of light emitting elements connected in parallel equal to each other.

[0010]

According to a first aspect of the present invention, a plurality of light emitting elements, a total current amount setting means for setting a total amount of currents flowing through these light emitting elements, and a current for which a total amount is set are set. Current distribution means for distributing to these light emitting elements,
The light emitting element drive circuit includes a current amount detecting means for detecting the amount of current flowing through the light emitting element and a distribution ratio changing means for changing the current distribution ratio by the current distributing means so that the current amounts flowing through the light emitting element are equal to each other. It is equipped.

That is, according to the first aspect of the invention, the total amount of current flowing through the plurality of light emitting elements is set by the total current amount setting means, and the total amount of current flowing through the respective light emitting elements is equal to each other. The amount is distributed. By distributing the current for which the sum total is set, the amount of current flowing through each light emitting element can be adjusted without changing the total amount.

In a second aspect of the present invention, a plurality of light emitting elements, a sum total application time setting means for setting a total time for applying a constant voltage to these light emitting elements within a predetermined unit time, and a constant voltage The total time distribution means for distributing the total time applied to these light emitting elements, the current amount detection means for detecting the amount of current flowing through each light emitting element, and the average amount of current flowing through each light emitting element in a predetermined unit time are The light emitting element drive circuit is provided with a distribution ratio changing unit for changing the distribution ratio of the total time by the total time distribution unit so as to be equal to each other.

That is, in the second aspect of the invention, the total current amount is set by the total time for applying a constant voltage to the light emitting element during a predetermined unit time. The average current amount flowing through each light emitting element is made equal to each other by adjusting the distribution ratio of the total time of applying the voltage.

According to the third aspect of the invention, a plurality of light emitting elements, a plurality of switches each of which is connected in series with each of the light emitting elements and one end of which is connected to a predetermined voltage source, and which has a constant width and a predetermined width. A pulse generating means for outputting a pulse signal having repeated pulses and a switch to which this pulse signal is inputted as a conduction control signal for controlling conduction are selectively switched and a switch to which a pulse signal is not inputted is made non-conductive. Continuity control signal input destination switching means, current amount detecting means for detecting the amount of current flowing through each light emitting element, and the switch to which a pulse signal is input are sequentially changed so that the average amount of current flowing through each light emitting element becomes equal to each other. And an input destination changing means for controlling the light emitting element.

That is, according to the third aspect of the invention, the total conduction time in a unit time is set by the pulse width of the pulse signal output from the pulse generating means. Therefore, the total amount of current flowing through the plurality of light emitting elements is adjusted by the pulse width. The switches to which this pulse signal is input as the conduction control signal are sequentially switched. The longer the pulse signal is input, the longer the time the switch is conducting, and the larger the average current amount of the light emitting element. On the other hand, if the pulse signal is input for a short time, the amount of current flowing through the light emitting element also decreases. Therefore, the average current amount flowing in each light emitting element is adjusted to be equal by sequentially switching the switches to which the pulse signals are input.

According to another aspect of the present invention, there are provided two light emitting elements, a switch connected to each of the light emitting elements in series and having one end connected to a predetermined voltage source, and a pulse having a predetermined width and a predetermined period. First pulse generating means for outputting a repeating first pulse signal, and second pulse generating means for outputting a second pulse signal in which a pulse having an arbitrary width is repeated at a predetermined cycle longer than the fixed cycle, This second
The first pulse signal is input to one of the switches as a conduction control signal for controlling the conduction of the pulse signal while the pulse of the pulse signal is being output, and the switch is set to the non-conduction state while the pulse is not being output. The first conduction control signal input switching means and the other switch during the period in which the pulse of the second pulse signal is not output are the first conduction control signal as the conduction control signal.
Second conduction control signal input switching means for making the switch non-conductive during the period in which the pulse signal is input and the pulse is output, and current amount detection means for detecting the amount of current flowing through the light emitting element, respectively. Pulse width changing means for changing the pulse width of the second pulse signal output from the second pulse generating means so that the average current amounts of the second pulse signals flowing through the respective light emitting elements in one cycle become equal to each other. And are provided in the light emitting element drive circuit.

That is, in the fourth aspect of the invention, the total amount of the currents flowing through the two light emitting elements is set by the pulse width of the first pulse signal output from the first pulse generating means. Then, by changing the pulse width of the second pulse signal, the time distribution in which a constant voltage is applied to the light emitting element is changed to equalize the average amount of current flowing.

According to the fifth aspect of the invention, the current flowing through each light emitting element is smoothed by the capacitor.

That is, according to the fifth aspect of the present invention, even if the switch is intermittently conducted, the current flowing through the capacitor is smoothed by the capacitor, so that the light emitting element can continuously output light.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to embodiments.

FIG. 1 shows a luminescent element according to an embodiment of the present invention.
It is a diagram showing an outline of a configuration of a child drive circuit. With Figure 4
The same parts are designated by the same reference numerals and the description thereof will be omitted as appropriate.
You. The pulse signal 15 output from the pulse generator 14 is the first
And the second AND circuit 21 ₁, 22_TwoThrough the first
Analog switch 12₁And the second analog switch 12
_TwoHas been entered. First light emitting element 11₁And resistor 1
3₁Connection point 22₁And the second light emitting element 11_TwoAnd resistance
Bowl 13_TwoConnection point 22_TwoAre the pulse width modulators 23
Is connected to Resistor 13₁, 13_TwoAre identical to each other
Has become the resistance value of. And connection point 22₁, 22_TwoTo
Is an electric current corresponding to the amount of current flowing through the corresponding light emitting element
Pressure V₁, V_TwoIs to appear.

The pulse width modulator 23 includes a pulse generator 14
The ratio control signal 24, which is a pulse signal having a period sufficiently longer than the period of the pulse signal 15 output by the above, is generated. The duty ratio of the ratio control signal 24 changes according to the ratio of the voltages V ₁ and V ₂ appearing at the connection points 22 ₁ and 22 ₂ . For example, the second light emitting element 1
If the average amount of current flowing through 1 ₂ is larger than the average amount of current flowing through the first light emitting element 11 ₁ , the ratio control signal 2
The output period of the pulse signal in No. 4 is shortened to change the duty ratio. On the other hand, the average amount of current flowing through the second light emitting element 11 ₂ is
When it becomes smaller than that flowing in the light emitting element 11 ₁ , the duty ratio is increased and the output period of the pulse signal is lengthened. In this way, the light emitting device 1
The duty ratio of the ratio control signal 24 is changed so that the average current amounts flowing through 1 ₁ and 11 ₂ are equal to each other.

The ratio control signal 24 has its logical value inverted by the inversion circuit 25 and then input to the _first AND circuit 21 ₁ . The signal output from the inverting circuit 25 will be referred to as an inverting control signal 26. Second AND circuit 21 ₂
The ratio control signal 24 is input as it is without being inverted. When the value of the ratio control signal 24 is high level, the pulse signal 15 passes through the second AND circuit 21 ₂ and is input to the _second analog switch 12 ₂ . On the other hand, when the value of the ratio control signal 24 is low level, the pulse signal 15 passes through the first AND circuit 21 ₁ and is input to the _first analog switch 12 ₁ . Therefore, the pulse generator 14
The pulse signal 15 output from the first analog switch 12 ₁ and the second analog switch 12 corresponds to the duty ratio of the ratio control signal 24 output from the pulse width modulator 23.
Divided into _two . That is, the first light emitting element 11 ₁ and the second light emitting element 11 ₁ in one cycle of the ratio control signal 24.
The total sum of the currents flowing in ₂ is adjusted by the duty ratio of the pulse signal 15 output from the pulse generator 14. On the other hand, the first light emitting element 11 ₁ and the second light emitting element 11
The ratio of the amount of current flowing through ₂ is adjusted by the duty ratio of the ratio control signal 24 output from the pulse width modulator 23.

FIG. 2 shows a signal waveform in each part of the light emitting element drive circuit shown in FIG. The duty ratio of the pulse signal 15 (a in the figure) output from the pulse generator 14 is set to 50% here. The output signal of the second AND circuit 21 ₂ (c in the figure) is
While the ratio control signal 24 (b in the figure) output from the pulse width modulator 23 is at the high level, it becomes equal to the pulse signal 15. On the other hand, the output signal of the first AND circuit 21 ₁ (d in the figure) becomes equal to the pulse signal 15 while the proportional control signal 24 is at low level. The sum of the conduction times of the analog switches 12 ₁ and 12 ₂ in one period 31 of the ratio control signal 24, that is, the sum of the amounts of current flowing through the first and second light emitting elements 11 ₁ and 11 ₂ is It is controlled by the duty ratio. On the other hand, the total current amount is calculated as the first light emitting element 11 ₁
The ratio to be distributed to the second light emitting element 11 ₂ corresponds to the duty ratio of the ratio control signal 24.

For example, the six pulses existing during the period 31 are the first light emitting element 11 ₁ and the second light emitting element 11 ₁ .
3 pieces are distributed to ₂ each. Up to time T ₁₁ , by equally distributing the pulses in this way, it is assumed that the average amount of current flowing through the first and second light emitting elements 11 ₁ and 11 ₂ was equal. However, after time T _11, the current amount of the _first light emitting element 11 ₁ becomes larger than the current amount of the second light emitting element 11 ₂ in the state where the pulses are equally distributed due to the influence of the ambient temperature and the secular change. It is assumed that there is an imbalance in the amount of flowing current. At this time, the pulse width modulator 2
3, two pulses in cycle 32 first to the light emitting element 11 ₁ in order to equalize the amount of current flowing through the first and second light emitting elements 11 _1, 11 _2, the second to the light emitting element 11 ₂ Four
The duty ratio of the ratio control signal 24 is changed so that the individual pulses are distributed. Even if the pulse distribution ratio is changed in this way, the first and second light emitting elements 11 ₁ , 1
Since the total amount of current flowing through 1 ₂ does not change, the distribution ratio and the total amount can be controlled independently.

FIG. 3 shows a structure of a high power laser diode light source using a light emitting element drive circuit according to an embodiment of the present invention. The same circuit parts as those in FIG. 1 are designated by the same reference numerals and the description thereof will be omitted as appropriate. This high-power laser diode light source uses two laser diodes 41 ₁ and 41 ₂ as light emitting elements. The optical outputs of the laser diodes 41 ₁ and 41 ₂ are the optical fibers 4 respectively.
It is guided to the polarization combiner 42 through 3 ₁ and 43 ₂ .
The polarization combiner 42 includes two laser diodes 41 ₁ , 4
1 ₂ optical outputs coupled to the respective polarization-maintaining optical fiber, those light coupled into one optical path by the polarization separation film and outputs to the optical fiber 43 _3.

This high-power laser diode light source can obtain a high optical output by polarization-combining the optical outputs of the _two laser diodes 41 ₁ and 41 ₂ . Also, two laser diodes 41 ₁ , 4
By taking the sum of the optical outputs of 1 ₂ to reduce the amount of current flowing to each, the deterioration of the laser diode is reduced, and the reliability as a light source is improved.

As the analog switch, a MOS type electric switch is used.
Field effect transistor 44₁, 44 _TwoIs used. M
OS type field effect transistor 44₁, 44_TwoIs 5
A gate voltage as low as a volt can produce a few amperes of electricity.
The laser diode can be switched at high speed.
It is suitable for the drive circuit. MOS field effect transistor
Dista 44₁, 44_TwoThe source is grounded at one end
Condenser 45₁, 45_TwoIs connected. Con
Densa 45₁, 45_TwoIs the current flowing through the laser diode
Has the function of smoothing. Time constant is pulse width modulation
More than the period of the ratio control signal 24 output from the instrument 23
It's getting longer. Capacitor 45₁, 45_TwoIs a pulse
Pulse signal 15 and ratio control signal output from genital organ 14
The intermittent flow of current due to 24 is smoothed and the current is continuously supplied.
It is designed to flow. As a result, the laser diode
Do 41₁, 41_TwoLight output is continuous light.

Since it is smoothed by the capacitors 45 ₁ 45 ₂ , a voltage corresponding to the smoothed current amount flowing in the laser diodes 41 ₁ and 41 ₂ continuously appears at the connection points 22 ₁ and 22 ₂ . The pulse width modulator 23 has a connection point 2
The duty ratio of the ratio control signal 24 is changed so that the voltages appearing at 2 ₁ and 22 ₂ become equal. For example, two laser diodes 41 ₁ , 41 ₂
Even if an imbalance occurs in the currents flowing due to the variation in the characteristics of, the pulse width modulator 23 adjusts so that the ratios of the currents flowing in the laser diodes 41 ₁ and 41 ₂ become equal. As a result, two laser diodes 41
The degree of deterioration of ₁ and 41 ₂ can be made uniform, and a highly reliable high-power laser diode light source can be obtained.

[0030]

As described above, according to the invention described in claim 1, since the total amount of current is set and distributed so that the amounts of current flowing through the respective light emitting elements are equal to each other, the total sum is obtained. The amount of current flowing through each light emitting element can be easily adjusted without changing the amount.

According to the second aspect of the invention, the total current amount is set by the total time for applying a constant voltage. Also, by distributing the total time, the average amount of current flowing through each light emitting element is made equal. The distribution of the voltage application time can be easily adjusted by, for example, opening and closing a switch, so that the circuit configuration of the light emitting element drive circuit can be simplified.

Further, according to the third aspect of the invention, since the switches to which the pulse signals are input are sequentially switched to distribute the total current amount, each light emitting element can be changed without changing the total current amount. The ratio of the amount of current flowing through can be easily adjusted.

According to the invention described in claim 4, the amount of current flowing through the two light emitting elements can be changed by the pulse width of the second pulse signal output from the second pulse generating means. The circuit configuration for distribution is simplified, and the light emitting element drive circuit can be simplified.

Further, according to the invention of claim 5, the current flowing through the capacitor is smoothed even when the switch is intermittently conducted, so that the light emitting element can continuously output light.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an outline of a configuration of a light emitting element drive circuit in an embodiment of the present invention.

FIG. 2 is various waveform charts showing signal waveforms in respective parts of the light emitting element drive circuit shown in FIG.

FIG. 3 is a block diagram showing a configuration of a high-power laser diode light source using a light emitting element drive circuit according to an embodiment of the present invention.

FIG. 4 is a block diagram showing an outline of a configuration of a light emitting element drive circuit that operates conventionally used light emitting elements in parallel.

5 is a waveform diagram showing a waveform of a signal output from a pulse generator of the light emitting element drive circuit shown in FIG.

[Explanation of symbols]

 11 Light-Emitting Element 12, 44 Analog Switch 13 Resistor 14 Pulse Generator 21 AND Circuit 23 Pulse Width Modulator 25 Inversion Circuit 41 Laser Diode 45 Capacitor

Claims (5)

(57) [Claims] 1. A plurality of light emitting elements, a total current amount setting means for setting a total amount of currents flowing through these light emitting elements, and a current distributing means for distributing the currents having the set total amount to these light emitting elements. The light emitting device includes a current amount detecting unit that detects the amount of current flowing in each of the light emitting devices, and a distribution ratio changing unit that changes the current distribution ratio of the current distributing unit so that the amounts of current flowing in the light emitting devices become equal to each other. A light emitting element drive circuit characterized by the above. 2. A plurality of light emitting elements, a sum total application time setting means for setting a total time for applying a constant voltage to these light emitting elements within a predetermined unit time, and a total sum of the constant voltages applied. The total time distribution means for distributing time to these light emitting elements, the current amount detection means for detecting the amount of current flowing through each of the light emitting elements, and the average amount of current flowing through each light emitting element in the predetermined unit time are equal to each other. And a distribution ratio changing unit for changing the distribution ratio of the total time by the total time distribution unit. 3. A plurality of light emitting elements, a plurality of switches each of which is connected to each of the light emitting elements in series and one end of which is connected to a predetermined voltage source, and a pulse signal in which a pulse of a predetermined width is repeated at a constant cycle. A pulse generation means for outputting and a switch for inputting the pulse signal as a conduction control signal for controlling conduction thereof are selectively switched and a switch for inputting a conduction control signal for making a switch to which the pulse signal is not input nonconductive Means, a current amount detection means for detecting the amount of current flowing through each of the light emitting elements, and an input destination change for sequentially changing the switches to which the pulse signals are input so that the average amount of current flowing through each light emitting element becomes equal And a light emitting element drive circuit. 4. A light emitting element, a switch connected to each of these light emitting elements in series and having one end connected to a predetermined voltage source, and a first pulse signal in which a pulse of a predetermined width is repeated at a constant cycle. And a second pulse generating means for outputting a second pulse signal in which a pulse having an arbitrary width is repeated at a predetermined cycle longer than the fixed cycle, and the second pulse signal. The first pulse signal is input to one of the switches as a conduction control signal for controlling the conduction of the switch during the period in which the pulse is output, and the switch is turned off during the period in which the pulse is not output. Of the conduction control signal input switching means and the other switch while the pulse of the second pulse signal is not being output, the first pulse signal is inputted to the other switch as the conduction control signal. The second conduction control signal input switching means for making the switch non-conductive during the output period of, the current amount detecting means for detecting the amount of current flowing through the light emitting element, and the current flowing through each light emitting element. The second pulse signal is adjusted so that the average current amounts in one cycle become equal to each other.
And a pulse width changing means for changing the pulse width of the second pulse signal output from the pulse generating means. 5. The light emitting element drive circuit according to claim 2, wherein a current flowing through each light emitting element is smoothed by a capacitor.