JP5032166B2 - Light emitting element drive circuit - Google Patents

Description

  The present invention relates to a light emitting element driving circuit for driving a light emitting element such as a light emitting diode or a laser diode.

  Recent advances in the field of data transmission by optical communication are remarkable, and various light emitting elements such as light emitting diodes and laser diodes are used in such fields.

  Incidentally, in order to drive a light emitting element such as a light emitting diode or a laser diode, a voltage equal to or higher than the forward voltage Vf specific to the light emitting element is required. For example, in a general white light emitting diode, the forward voltage Vf is 3.6 V. Therefore, in order to light this white light emitting diode, a voltage source higher than this voltage is required.

  However, in a commonly used portable electronic device, a dry battery or a rechargeable battery is used as a voltage source. However, the rated voltage is 3.7 V or less, and the white light emitting diode cannot be turned on as it is. Even if it can be lit, since the battery voltage decreases with time, it cannot be lit without completing a sufficient battery life.

  Therefore, conventionally, in a portable electronic device using a dry battery or a rechargeable battery as a voltage source, a booster circuit that boosts the voltage of the voltage source to a stable voltage higher than 3.6 V is used in order to stably light the white light emitting diode. ing.

  On the other hand, when such light-emitting elements such as light-emitting diodes and laser diodes are used in the field of optical communication, it is necessary to blink at high speed in order to perform data transmission, and a modulation circuit that switches on and off is also indispensable.

  FIG. 6 shows an example of a booster circuit adopting a chopper method, in which the positive terminal of the DC power source 1 is connected to the output terminal t1 through a series circuit of the booster coil 2 and the diode 3 of the polarity shown, and the negative terminal is It is connected to the output terminal t2. A boost switch 4 is connected between the connection point of the boost coil 2 and the diode 3 and the output terminal t1, and a smoothing capacitor 5 is connected between the output terminals t1 and t2. Here, the diode 3 prevents the energy stored in the smoothing capacitor 5 from flowing backward and discharging when the boost switch 4 is turned on. The timing for turning on / off the booster switch 4 is controlled by a control circuit (not shown) based on the voltage generated between the output terminals t1 and t2. Further, the smoothing capacitor 5 is provided so that the boosted output voltage falls within a certain range, and can supply a stable voltage to the load side. In the case where the light emitting element is stably turned on as in the lighting device, the smoothing capacitor 5 functions effectively.

The booster circuit first turns on the booster switch 4 to cause a current to flow from the DC power source 1 to the booster coil 2 and charge the booster coil 2 with the energy. Next, by turning off the booster switch 4, a high voltage is generated from the booster coil 2 that is sufficiently charged with energy, and is stored in the smoothing capacitor 5 through the diode 3. Thereafter, the voltage boosted from both ends of the smoothing capacitor 5, that is, between the output terminals t1 and t2, is output by repeatedly turning on and off the boost switch 4.
A booster circuit employing such a chopper method is also disclosed in Patent Document 1, for example.

  On the other hand, FIG. 7 shows an example of a modulation circuit that causes a light emitting element to blink at high speed. A series circuit of a modulation switch 7, a light emitting element 8, and a current limiting mechanism 9 is connected between positive and negative terminals of a DC power supply 6. ing. Here, the DC power supply 6 can supply a voltage sufficient to light the light emitting element 8. The modulation switch 7 is turned on / off according to the data signal to be communicated, and the light emitting element 8 can be turned on / off. Further, the current limiting mechanism 9 is for preventing an excessive current from flowing through the light emitting element 8.

In such a modulation circuit, when the modulation switch 7 is turned on / off according to the data signal to be communicated, the light emitting element 8 is switched on / off according to the on / off of the modulation switch 7.
JP 2006-49423 A JP 2001-144597 A

  As described above, the booster circuit and the modulation circuit are conventionally prepared separately. For this reason, for example, a dry battery or a rechargeable battery is used as a voltage source as in a portable optical communication device, so a booster circuit is necessary. In addition, if a modulation circuit that blinks the light-emitting element at high speed is used to transmit the data signal, each circuit is provided independently, which increases the number of parts and increases the price. Moreover, since a circuit space is increased by arranging a plurality of circuits in parallel, there is a problem in that the size of the device is increased.

  Therefore, conventionally, a light emitting element driving circuit combining the booster circuit described in FIG. 6 and the modulation circuit described in FIG. 7 as shown in FIG. 8 has been considered. In this case, in FIG. 8, the same parts as those in FIGS. 6 and 7 are denoted by the same reference numerals, and the DC power source 1 is used in common, and the modulation switch 7, the light emitting element 8 and the current limiting are provided at both ends of the smoothing capacitor 5. A series circuit of the mechanism 9 is connected. A light emitting element driving circuit in which such a booster circuit and a modulation circuit are combined is also disclosed in Patent Document 2, for example.

  However, when the on / off operation of the boost switch 4 and the on / off operation of the modulation switch 7 are out of sync with each other, the light emitting element driving circuit shown in FIG. 8 tries to turn on the light emitting element 8 after the boost switch 4 is turned on. Even if the modulation switch 7 is turned on, the boosted output from the booster coil 2 may not be sufficiently supplied to the light emitting element 8, and the light emission of the light emitting element 8 becomes unstable, and the communication of the data signal is stabilized. The problem that it becomes impossible. Further, since the main purpose is to make the voltage across the smoothing capacitor 5 constant, a large capacitor that can store sufficient energy to supply stable energy to the booster coil 2 is used. In addition to the smoothing capacitor 5 and the booster coil 2, a large number of electronic components such as a diode 3, a booster switch 4 and a modulation switch 7 are used, which is still expensive due to the large number of components and the circuit space remains large. However, the device has not yet been downsized.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a light-emitting element driving circuit that can be reduced in size and weight and can realize a stable operation.

A light emitting element driving circuit according to the present invention includes a power source, a boosting unit that charges and discharges energy from the power source, generates a boosted output by discharging the energy, and light emission driven by an output boosted by the boosting unit. comprising a device, a charging operation of the energy from the power supply of said boosting means, and switching means for synchronously execute operation for supplying boosted output to the light emitting element by the energy discharge of said boosting means, said The switching means includes one movable contact piece, a first fixed contact piece, and a second fixed contact piece, the movable contact piece is connected to the boosting means, and the first fixed contact piece is Connected to the electrode of the power source, the second fixed contact is connected to the light emitting element, and the movable contact is alternately contacted with and separated from the first fixed contact and the second fixed contact. It is the structure which switches to .

  According to the present invention, it is possible to provide a light emitting element driving circuit which can be reduced in size and weight and can realize a stable operation.

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

(First embodiment)
FIG. 1 shows a schematic configuration of a light emitting element driving circuit according to a first embodiment of the present invention.
In FIG. 1, reference numeral 11 denotes a DC power source, and a dry battery or a rechargeable battery is used for the DC power source 11. Connected to the positive terminal of the DC power supply 11 is a changeover switch 13 as switching means for boosting and modulating via a boosting coil 12 as boosting means for boosting the power supply voltage.

  The booster coil 12 charges and discharges energy from the DC power supply 11 and generates an output obtained by boosting the power supply voltage by discharging the energy. The light-emitting diode 14 described later is driven by this boosted output. The step-up coil 12 used here has a small energy storage amount that enables charging of the light-emitting diode 14 for an extremely short time of about 1 microsecond.

  The changeover switch 13 has a movable contact piece 13a and two fixed contact pieces 13b and 13c to which the movable contact piece 13a is contacted and separated. The movable contact piece 13a is alternately brought into and out of contact with the fixed contact pieces 13b and 13c. In addition to the switching operation, a neutral state in which neither of the fixed contact pieces 13b and 13c is in contact is obtained. FIG. 1 shows a case where the movable contact piece 13a is positioned in a neutral state.

  The negative terminal of the DC power supply 11 is connected to the fixed contact 13 b of the changeover switch 13. The negative terminal of the DC power supply 11 is connected to the fixed contact piece 13c of the changeover switch 13 through a series circuit of a plurality of light emitting diodes 14 of the illustrated polarity as light emitting elements and a resistor 15 as current limiting means.

In this case, when the data signal is not modulated , the changeover switch 13 is positioned in a neutral state in which the movable contact piece 13a is not in contact with any of the fixed contact pieces 13b and 13c. Further, during the communication of the data signal, the movable contact piece 13a is alternately switched to the fixed contact pieces 13b and 13c, and the boosting coil 12 is charged with energy by switching the movable contact piece 13a to the fixed contact piece 13b. The operation of discharging the energy of the booster coil 12 and supplying the boosted output (high voltage) to the light emitting diode 14 by switching the movable contact 13a to the fixed contact 13c is executed in synchronization.

  Further, the change-over switch 13 is used to change the movable contact piece 13a to the fixed contact piece 13b side when the light-emitting diode 14 is turned on for a longer time than the light-emitting diode 14 whose turn-on / off pattern is determined by the data signal. (ON time) is increased to increase the energy charged in the booster coil 12, and the switching time (ON time) of the movable contact piece 13a to the fixed contact piece 13c is lengthened to increase the output from the booster coil 12. When the voltage is supplied to the light emitting diode 14 over time, and when the lighting time of the light emitting diode 14 is shortened, the switching time (ON time) of the movable contact 13a to the fixed contact 13b is shortened. While boosting the coil 12 with less energy, the switching time (ON time) of the movable contact 13a to the fixed contact 13c is shortened to increase the boost coil. Only a short time a high voltage output from the 2 supplied to the light emitting diode 14.

In such a configuration, when the data signal is not modulated , it is assumed that the movable contact piece 13a of the changeover switch 13 is in a neutral state where it does not contact any of the fixed contact pieces 13b and 13c. When communication of the data signal is started from this state, the movable contact piece 13a is alternately switched to the fixed contact pieces 13b and 13c by the data signal at this time.

  In this case, when the movable contact piece 13a is first switched to the fixed contact piece 13b side and contacted (ON) between them (period A1 in FIG. 2A), a current flows from the DC power supply 11 to the booster coil 12, The energy is charged in the booster coil 12.

  Next, when the movable contact piece 13a is switched to the fixed contact piece 13c side and contacted (turned on) between them (period B1 in FIG. 2B), the energy charged in the booster coil 12 is released and boosted. High voltage is generated. The high voltage of the booster coil 12 is supplied to the light emitting diode 14. As a result, a sufficient voltage equal to or higher than the inherent forward voltage is applied to the light emitting diode 14 to light up (emit light). Further, when the output of the booster coil 12 decreases with time and becomes equal to or lower than the forward voltage of the light emitting diode 14, the light emitting diode 14 is turned off.

  Thereafter, similarly, the movable contact piece 13a of the changeover switch 13 is alternately switched to the fixed contact pieces 13b and 13c according to the data signal, whereby the light emitting diode 14 can be turned on and off.

  In this case, when the lighting time of the light emitting diode 14 is lengthened in accordance with the data signal to be communicated, the switching time of the movable contact piece 13a to the fixed contact piece 13b side is lengthened as shown in the period A2 in FIG. As a result, the amount of energy charged in the booster coil 12 is increased, and the switching time of the movable contact piece 13a to the fixed contact piece 13c side is lengthened as shown in the period B2 in FIG. The applied high voltage is supplied to the light emitting diode 14 over time. Conversely, when shortening the lighting time of the light emitting diode 14, the switching time (ON time) of the movable contact 13a to the fixed contact 13b is shortened to reduce the amount of energy charged in the booster coil 12, and the movable contact 13b is movable. The switching time of the contact piece 13a to the fixed contact piece 13c side is also shortened, and the high voltage output from the booster coil 12 is supplied to the light emitting diode 14 for a short time.

  Therefore, in this way, when the movable contact 13a of the changeover switch 13 is switched to the fixed contact 13b, a current flows from the DC power source 11 to the booster coil 12, the energy is charged in the booster coil 12, and then When the movable contact piece 13a is switched to the fixed contact piece 13c, charging energy is discharged to the booster coil 12, a high voltage is supplied to the light emitting diode 14, and the light emitting diode 14 is driven. The light-emitting diode 14 is turned on and off by alternately switching the movable contact piece 13a of the changeover switch 13 to the fixed contact pieces 13b and 13c according to the signal. That is, the light emitting element driving circuit of the present invention is designed to turn on and off the light emitting diode 14 while the conventional circuit configuration shown in FIG. 8 focuses on making the voltage across the smoothing capacitor constant. It was aimed. This eliminates the need for the light-emitting diode 14 to emit light stably in the first place, and therefore it is not necessary to make the supplied voltage constant, so that the smoothing capacitor can be omitted from the circuit elements of FIG. Further, since the smoothing capacitor is omitted, a diode for preventing unnecessary discharge from the smoothing capacitor is also unnecessary, and can be omitted from the circuit elements of FIG. Further, in the circuit configuration shown in FIG. 8, a boost switch and a modulation switch are provided, respectively. However, in the circuit of the present embodiment, these can be combined into one so that a desired switch operation can be obtained by the changeover switch 13. Therefore, the number of switches can be reduced from the circuit elements of FIG. Further, as described above, conventionally, the focus has been on making the voltage across the smoothing capacitor constant, and the booster coil has also been required to be sufficiently large in order to supply stable energy. In the light emitting element driving circuit, it is only necessary to charge the energy for an extremely short time of about 1 microsecond only when the light emitting diode 14 is turned on. Therefore, a small-sized one with a small energy storage amount is used. be able to. As described above, according to the circuit of the present invention, the reduction and common use of circuit elements have been actively realized, so that the device can be reduced in size and weight by being incorporated in a portable optical communication device. Can do.

  Further, the charging of the booster coil 12 by switching the movable contact 13a to the fixed contact 13b of the changeover switch 13 and the discharging of the energy of the booster coil 12 by switching to the fixed contact 13c of the movable contact 13a are performed. By performing each operation in synchronism, the charging energy of the booster coil 12 can be reliably and sufficiently supplied to the light emitting diode 14, so that the light emission of the light emitting diode 14 is always stable and data signal communication is possible. It can be performed stably.

  In the above description, the resistor 15 as the current limiting means has been described. However, the resistor 15 is not limited as long as it takes the form of current limiting, and the resistor 15 can be omitted depending on the operating conditions of the circuit.

(Second Embodiment)
Next, a light emitting element driving circuit according to a second embodiment of the present invention will be described with reference to FIG.

  In FIG. 3, the changeover switch 13 is replaced with two step-up switches and a modulation switch. In this case, the first bipolar transistor 16 is connected as a boost switch between the boost coil 12 and the negative electrode end of the DC power supply 11, and the second bipolar transistor is used as a modulation switch between the boost coil 12 and the light emitting diode 14. Transistor 17 is connected.

  The first bipolar transistor 16 has a collector connected to the booster coil 12 and an emitter connected to the negative terminal of the DC power supply 11. A control signal 16 a is supplied to the base and is turned on, whereby a current is supplied from the DC power supply 11 to the booster coil 12. The boosting coil 12 is charged with the energy. The second bipolar transistor 17 has a collector connected to the booster coil 12 and an emitter connected to the light emitting diode 14, respectively, and the base is supplied with a control signal 17a to turn on, thereby discharging the energy of the booster coil 12 and boosting the voltage. The output is supplied to the light emitting diode 14 to light it.

In this case, the first and second bipolar transistors 16 and 17 are both turned off when the data signal is not modulated, and are turned on and off in synchronization during the modulation of the data signal. The operation of charging the boosting coil 12 by turning on 16 and the operation of supplying the light emitting diode 14 with the output (high voltage) of the boosted coil 12 discharged and boosted by turning on the second bipolar transistor 17. Run synchronously.

  Further, the first and second bipolar transistors 16 and 17 have a first bipolar transistor 16 when the lighting time of the light emitting diode 14 is made longer than the light emitting diode 14 whose lighting and extinguishing patterns are determined by the data signal. The on-time of the second bipolar transistor 17 is increased by increasing the on-time of the second booster coil 12, and the high voltage output from the booster coil 12 is increased over time by the light-emitting diode 14 On the contrary, when the lighting time of the light emitting diode 14 is shortened, the on-time of the first bipolar transistor 16 is shortened to reduce the energy charged in the booster coil 12, and the second bipolar transistor 17 The high voltage output from the booster coil 12 is reduced for a short time by shortening the ON time. Supplied to the photodiode 14.

  Others are the same as those in FIG. 1, and the same parts are denoted by the same reference numerals.

In such a configuration, when the data signal is not modulated , the first and second bipolar transistors 16 and 17 are both turned off. When the communication of the data signal is started from this state, as shown in FIGS. 4A and 4B, the control signal 16a corresponding to the data signal is applied to the bases of the first and second bipolar transistors 16 and 17, respectively. 17a is provided, and the first and second bipolar transistors 16 and 17 are operated alternately.

  In this case, when the first bipolar transistor 16 is first turned on by the control signal 16a (period C in FIG. 4A), a current flows from the DC power source 11 to the booster coil 12, and the energy is charged in the booster coil 12. The Next, when the second bipolar transistor 17 is turned on by the control signal 17a (period D in FIG. 4B), the fully charged energy is released to the booster coil 12, and a boosted high voltage is generated. The high voltage of the booster coil 12 is supplied to the light emitting diode 14. As a result, a sufficient voltage equal to or higher than the inherent forward voltage is applied to the light emitting diode 14 to light up (emit light). Further, when the output of the booster coil 12 decreases with time and becomes equal to or lower than the forward voltage of the light emitting diode, the light emitting diode 14 is turned off.

  Thereafter, similarly, the first and second bipolar transistors 16 and 17 are alternately turned on and off according to the data signal, whereby the light emitting diode 14 can be turned on and off.

  Therefore, even in this case, the same effect as that of the first embodiment can be obtained. In the second embodiment, since the first and second bipolar transistors 16 and 17 are used as the boost switch and the modulation switch, a high-speed operation of about 1 MHz, for example, is possible with respect to the data signal. Further practical application of portable optical communication equipment can be expected.

  In the second embodiment, bipolar transistors are used as the boost switch and the modulation switch. However, the transistors are not limited to bipolar transistors as long as they actually take the form of switches. Also in this embodiment, the resistor 15 is used as current limiting means. However, the resistor 15 is not limited as long as it takes the form of current limiting, and the resistor 15 can be omitted depending on the operating conditions of the circuit. It is.

(Third embodiment)
Next, a light emitting element driving circuit according to a third embodiment of the present invention will be described with reference to FIG.

  In FIG. 5, as in the second embodiment, the first bipolar transistor 16 is used as a boost switch and the second bipolar transistor 17 is used as a modulation switch, and the second bipolar transistor 17 is connected to the light emitting diode 14. The resistor 15 is connected. In this case, the second bipolar transistor 17 has a collector connected to the light emitting diode 14 and an emitter connected to the resistor 15, and a control signal 17 a is supplied to the base to be turned on to generate a high voltage from the boost coil 12 and emit light. The light is supplied to the diode 14 and the light emitting diode 14 is turned on. Further, a transistor 18 is connected as a current limiting switching element between the base of the second bipolar transistor 17 and the negative terminal of the DC power supply 11. In this case, the transistor 18 has a collector connected to the base of the second bipolar transistor 17, an emitter connected to the negative terminal of the DC power supply 11, and a base connected to the emitter of the second bipolar transistor 17.

  Others are the same as those in FIG. 3, and the same portions are denoted by the same reference numerals.

  According to such a configuration, when the current flowing through the light-emitting diode 14 is small and the voltage across the resistor 15 is low, the transistor 18 remains off, and the current flowing through the light-emitting diode 14 passes through the second bipolar transistor 17 and the resistor. Flows through 15. Further, when the current flowing through the light emitting diode 14 becomes very large and the voltage across the resistor 15 increases, a part of the current supplied to the base of the second bipolar transistor 17 flows into the transistor 18, and accordingly, the second The current flowing through the bipolar transistor 17 is suppressed. In this way, the current flowing through the light emitting diode 14 is limited by the action of the transistor 18 and is controlled so that an appropriate current always flows through the light emitting diode 14.

  Therefore, even if it does in this way, the effect similar to 1st Embodiment can be acquired, Furthermore, since the electric current which flows into the light emitting diode 14 can always be controlled to an appropriate state, the light emitting diode 14 can be light-emitted stably. Can do.

  In the third embodiment, bipolar transistors are used as the boost switch and the modulation switch. However, the transistors are not limited to bipolar transistors as long as they actually take the form of switches.

  In addition, this invention is not limited to the said embodiment, In the implementation stage, it can change variously in the range which does not change the summary. For example, in the above-described embodiment, the light-emitting diode 14 is described as the light-emitting element. However, the present invention can be similarly performed when a laser diode is used instead of the light-emitting diode. In the above-described embodiment, the light emitting diodes are turned on and off for signal data communication. However, the light emitting diodes 14 are turned on and off at an extremely high speed without feeling flickering. It can also be used as a lighting device.

  Furthermore, the above embodiments include inventions at various stages, and various inventions can be extracted by appropriately combining a plurality of disclosed constituent elements. For example, even if some constituent requirements are deleted from all the constituent requirements shown in the embodiment, the problem described in the column of the problem to be solved by the invention can be solved, and is described in the column of the effect of the invention. If the above effect is obtained, a configuration from which this configuration requirement is deleted can be extracted as an invention.

1 is a diagram showing a schematic configuration of a light emitting element driving circuit according to a first embodiment of the present invention. The figure which shows the operation | movement sequence of 1st Embodiment. The figure which shows schematic structure of the light emitting element drive circuit concerning the 2nd Embodiment of this invention. The figure which shows the operation | movement sequence of 2nd Embodiment. The figure which shows schematic structure of the light emitting element drive circuit concerning the 3rd Embodiment of this invention. The figure which shows schematic structure of an example of the conventional booster circuit. The figure which shows schematic structure of an example of the conventional modulation circuit. The figure which shows schematic structure of the drive circuit of the light emitting element which combined the conventional booster circuit and the modulation circuit.

Explanation of symbols

11 ... DC power supply, 12 ... Boost coil 13 ... Changeover switch, 13a ... Movable contact piece 13b. 13c: fixed contact 14: light emitting diode, 15: resistor 16 ... first bipolar transistor 17 ... second bipolar transistor 18 ... transistor

Claims (2)

Power supply,
Boosting means for charging / discharging energy from the power source and generating boosted output by discharging the energy;
A light emitting element driven by an output boosted by the boosting means;
Charging means for charging energy from the power source of the boosting means, and switching means for synchronously executing an operation of supplying an output boosted by energy discharge of the boosting means to the light emitting element ,
The switching means includes
Including one movable contact piece, a first fixed contact piece, and a second fixed contact piece,
The movable contact piece is connected to the boosting means;
The first fixed contact piece is connected to the electrode of the power source;
The second fixed contact piece is connected to the light emitting element;
The light emitting element driving circuit according to claim 1, wherein the movable contact piece is switched so as to be alternately contacted with and separated from the first fixed contact piece and the second fixed contact piece . The switching means includes
During the data communication by the blinking of the light emitting element, the movable contact piece is switched so as to alternately contact and separate from the first fixed contact piece and the second fixed contact piece according to a data signal. The light emitting element drive circuit according to claim 1.

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