JP2011108778A - Laser diode driving device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve a problem which arises in a breakdown voltage when using a miniaturized semiconductor element for a laser diode driving device of a high operating voltage such as a short wavelength laser, since the breakdown voltage tends to lower while high frequency characteristics are improved by the miniaturization of the semiconductor element. <P>SOLUTION: The laser diode driving device includes: a variable current source (1) capable of adjusting a current to be made to flow to a laser diode; a current driving circuit (2) capable of amplifying the output current of the variable current source; operation detection means (6, 7, 8) for detecting the operating state of the laser diode (5); a protective circuit (3) operated so as to secure the breakdown voltage of the current driving circuit (2) when not making the laser diode (5) perform a light emitting operation; and a protective voltage generation circuit (4) for generating a voltage capable of securing the breakdown voltage of the current driving circuit (2) and the protective circuit (3) and transmitting it to the protective circuit (3). <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a laser diode driving device including a circuit for current driving a laser diode.

  In recent years, devices equipped with a short-wavelength laser diode used for an optical head for Blu-ray Disc have become widespread. Since short-wavelength laser diodes tend to have a higher operating voltage than red or infrared laser diodes, it is necessary to set the power supply voltage of the laser diode drive device to be higher according to the operating voltage of the laser diode. was there. However, with the progress of miniaturization of the semiconductor element structure, when such a miniaturized semiconductor element is used in the laser diode driving device, there may be a problem in terms of breakdown voltage for preventing dielectric breakdown. Therefore, when using a low breakdown voltage semiconductor element, it is necessary to ensure a breakdown voltage depending on the circuit configuration.

  Hereinafter, a conventional laser diode driving device will be described with reference to FIG. FIG. 9 is a circuit diagram showing a configuration of a conventional laser diode driving device. As shown in FIG. 9, in the conventional laser diode driving apparatus, the cathode of the laser diode 94 is grounded, and a resistor 92 is connected between the anode of the laser diode 94 and the power supply voltage (Vcc) terminal. A resistor 93 is connected between the anode and the ground. The laser diode driving device is provided with a transistor 91 that allows a light emission current to flow through the laser diode 94 (see, for example, Patent Document 1 and FIG. 4).

The operation of the conventional laser diode driving apparatus configured as described above will be described below.
In the laser diode driving device shown in FIG. 9, in a non-operating state, a voltage Vce = Vcc−Vb is applied between the collector and emitter of the transistor 91 (a band gap voltage Vb is set in the laser diode 94). Yes.) On the other hand, in the operating state, a control voltage Va is applied between the base and emitter of the transistor 91 and a reverse current flows between the emitter and collector, whereby a collector current flows between the emitter and collector. The laser diode 94 is driven by this collector current, and laser light is emitted from the laser diode 94. Therefore, for example, when performing a recording operation, a reproducing operation, and an erasing operation on an optical disc, the output level of the laser light from the laser diode 94 is changed by controlling the signal level of the control voltage Va, Laser light having an output level corresponding to each operation is emitted.

  As described above, in the conventional laser diode driving apparatus, a resistance circuit including the resistor 92 connected between the anode of the laser diode 94 and the power supply voltage terminal and the resistor 93 connected between the anode of the laser diode 94 and the ground is used. The band gap voltage Vb is always applied to the non-operating laser diode 94, and a voltage lower than the power supply voltage Vcc (Vce = Vcc−Vb) is applied between the collector and the emitter of the transistor 91. Therefore, a breakdown voltage margin corresponding to the band gap voltage Vb is set in the transistor 91. For this reason, in the transistor 91, the withstand voltage condition is relaxed by the band gap voltage Vb, and it becomes possible to use a miniaturized semiconductor integrated circuit having excellent high frequency characteristics. Therefore, it is possible to perform high-density recording on, for example, a Blu-ray Disc by emitting laser light having a shorter wavelength to the laser diode 94.

JP 2002-232072 A JP 2003-101129 A

However, in the configuration of the conventional laser diode driving device described above, the withstand voltage of the transistor 91 that supplies current to the laser diode 94 is ensured, but two resistors 92 and 93 are connected in series between the power supply voltage terminal and the ground. Therefore, current always flows between the power supply voltage terminal and the ground. Further, the anode voltage (Vb) of the laser diode 94 is always determined, and even when the laser diode 94 is not operated to emit light, a current always flows through the laser diode 94. However, there are problems of increase in power consumption, progress of deterioration of the laser diode 94, and danger due to minute light emission during standby.
The present invention solves the above-mentioned problems in the conventional laser diode driving device, and prevents the laser diode from emitting light while ensuring the withstand voltage of the circuit element that drives the laser diode when the laser diode is not operated to emit light. Then, it aims at providing the laser-diode drive device which can reduce an idling electric current.

In order to achieve the above object, a laser diode driving apparatus according to a first aspect of the present invention is a laser diode driving apparatus that drives a laser diode by a current driving circuit,
A protection circuit for outputting a voltage for fixing the output of the current driving circuit;
An operation detecting means for detecting an operating state of the laser diode;
A control voltage generation circuit for determining a control voltage input to the protection circuit according to a signal from the operation detection unit, and controlling an output voltage of the protection circuit interlocked with the control voltage;
The protection voltage generation circuit controls a control voltage to the protection circuit when the laser diode is not emitting light, so that a voltage applied to the current drive circuit is within a withstand voltage range of the current drive circuit. It is configured to be set. The laser diode driving apparatus according to the first aspect of the present invention configured as described above causes a breakdown to a semiconductor element used in the protection circuit by a voltage set by the protection voltage generation circuit when the laser diode is not operated to emit light. It is possible to operate so as to ensure the withstand voltage for prevention and to ensure the withstand voltage of the semiconductor element used in the current driving circuit in the protection circuit.

  According to a second aspect of the present invention, there is provided a laser diode driving apparatus according to the first aspect, further comprising a variable current source that adjusts a current flowing through the laser diode and transmits the current to the current driving circuit. Also good.

  According to a third aspect of the present invention, in the laser diode driving device according to the first aspect or the second aspect, the protection circuit generation circuit detects a control signal for controlling the variable current source, and The output voltage of the protection circuit may be controlled.

  According to a fourth aspect of the present invention, there is provided the laser diode driving device according to the first aspect or the second aspect, wherein the protection voltage generation circuit is configured to output an output voltage of the protection circuit based on an anode voltage of the laser diode. May be controlled.

  According to a fifth aspect of the present invention, there is provided a laser diode driving apparatus according to the first or second aspect based on a control signal for adjusting the current flowing through the laser diode by the operation detecting means. The operating state of the laser diode may be detected.

  According to a sixth aspect of the present invention, there is provided the laser diode driving apparatus according to the first aspect or the second aspect, wherein the operation detecting means compares a current corresponding to a current flowing through the laser diode with a threshold value. A comparator that detects an operating state of the laser diode and outputs a state signal indicating the operating state to the protection voltage generation circuit.

  According to a seventh aspect of the present invention, there is provided a laser diode driving device according to any one of the first to sixth aspects, wherein the laser diode is a cathode common type, and the protection circuit includes a P-channel FET. The FET may have a gate connected to an output of the protection voltage generation circuit, a source of the FET connected to the current driving circuit, and a drain of the FET connected to an anode of the laser diode.

  According to an eighth aspect of the present invention, in the laser diode driving apparatus according to the first to sixth aspects, the laser diode is configured as an anode common type, and the protection circuit includes an N-channel FET. The gate of the FET may be connected to the output of the protection voltage generation circuit, the source of the FET may be connected to the current driving circuit, and the drain of the FET may be connected to the cathode of the laser diode.

  As described above, in the laser diode driving apparatus according to the present invention, the variable current source capable of adjusting the current flowing through the laser diode, the current driving circuit capable of amplifying the output current of the variable current source, and the laser Operation detection means for detecting the operating state of the diode, a protection circuit that operates to ensure the withstand voltage of the current drive circuit when the laser diode is not emitting light, and a voltage that can ensure the withstand voltage of the current drive circuit and the protection circuit are generated In addition, with the configuration having the protection voltage generation circuit that transmits to the protection circuit, the breakdown voltage of each component can be reliably ensured even when a miniaturized low breakdown voltage semiconductor element is used.

  The laser diode driving device of the present invention prevents idling of the laser diode while preventing a minute emission of the laser diode while ensuring a withstand voltage for preventing a dielectric breakdown with respect to a circuit element that drives the laser diode when the laser diode is not operated to emit light. The current can be reduced. Further, the laser diode driving device according to the present invention has a miniaturized structure because the breakdown voltage of the protection circuit and the current driving circuit is secured by the voltage set by the protection voltage generation circuit when the laser diode is not operated to emit light. It becomes possible to use a low-breakdown-voltage semiconductor element for a laser diode driving device.

1 is a block diagram showing a configuration of a laser diode driving apparatus according to a first embodiment of the present invention. FIG. 3 is a circuit diagram showing a specific example of the laser diode driving apparatus according to the first embodiment. The block diagram which shows the structure using the anode common type laser diode which is another structure of the laser-diode drive device of Example 1. FIG. FIG. 3 is a circuit diagram showing a specific example using an anode common type laser diode of the laser diode driving device shown in FIG. FIG. 3 is a block diagram showing a configuration of a laser diode driving apparatus according to a second embodiment of the present invention. The circuit diagram which shows a specific example of the laser-diode drive device of Example 2. The block diagram which shows the structure using the anode common type laser diode which is another structure of the laser-diode drive device of Example 2. FIG. FIG. 7 is a circuit diagram showing a specific example using an anode common type laser diode of the laser diode driving device shown in FIG. Circuit diagram showing the configuration of a conventional laser diode driving device

  Hereinafter, embodiments showing the best mode for carrying out the present invention will be described with reference to the accompanying drawings. In addition, the component which attached | subjected the same code | symbol in description of the Example performs the same function, a structure, and operation | movement, The description may be abbreviate | omitted when description overlaps.

  A laser diode driving apparatus according to a first embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a block diagram showing the configuration of the laser diode driving apparatus according to the first embodiment, and FIG. 2 is an example of a specific circuit configuration of the laser diode driving apparatus shown in FIG.

  As shown in FIG. 1, the laser diode driving apparatus of the first embodiment amplifies the variable current source 1 capable of adjusting the current for driving the laser diode 5 and the output current of the variable current source 1. A current driving circuit 2 capable of generating a current, and a protection circuit 3 that operates to ensure the withstand voltage of the current driving circuit 2 when the laser diode 5 is not operated to emit light, and that transmits an output current of the current driving circuit 2 to the laser diode 5; Protection voltage generation for generating a voltage that can secure the withstand voltage of the laser diode 5 whose anode is connected to the output of the protection circuit 3 and whose cathode is grounded, and the current driving circuit 2 and the protection circuit 3, and transmitting the voltage to the protection circuit 3 And a circuit 4. In the description of the present invention, the meaning of “transmission” includes the meaning of electrical operation of “application” and “input” in addition to the original meaning of transmission.

The operation of the laser diode driving apparatus of the first embodiment configured as described above will be described below.
In the laser diode driving apparatus according to the first embodiment, the variable current source 1 can adjust the current flowing through the laser diode 5, and the adjustment operation is controlled by a control signal X input to the variable current source 1. ing. Thus, the variable current source 1 can adjust the light emission power of the laser diode 5 according to the control signal X input from the variable current control line 6. Therefore, the control signal X is a signal that indirectly indicates the light emission operation state that is the operation state of the laser diode 5.
The current determined in the variable current source 1 to which the control signal X is input is transmitted to the current driving circuit 2. The current drive circuit 2 can amplify and output the transmitted current, and the amplified output current drives the laser diode 5 through the protection circuit 3. In the laser diode driving apparatus of the first embodiment, since the protection circuit 3 is provided, the output voltage of the current driving circuit 2 is fixed (determined) by the output voltage of the protection circuit 3 and the laser diode 5 is not operated to emit light. The withstand voltage for the current drive circuit 2 is ensured.

In the laser diode driving apparatus according to the first embodiment configured as described above, if the protection circuit 3 is not provided, the output of the current driving circuit 2 and the anode of the laser diode 5 are directly connected. Become. In the case of such a configuration, when the laser diode 5 is not operated to emit light, the anode voltage of the laser diode 5, that is, the output voltage of the current drive circuit 2 is a voltage substantially close to the GND potential. When the power supply of the circuit to be operated is 8 to 10 V, the current drive circuit 2 is configured by configuring the current drive circuit 2 with a low breakdown voltage semiconductor element (here, the low breakdown voltage means a voltage of about 7 V or less, for example). There is a problem that the withstand voltage cannot be secured.
Therefore, in the laser diode driving device of the first embodiment, the protection circuit 3 and the protection voltage generation circuit 4 are provided. For this reason, it becomes possible to fix (determine) the output voltage of the current drive circuit 2 with the output voltage of the protection circuit 3, and when the laser diode 5 is not operated to emit light, the current drive circuit configured with a low breakdown voltage semiconductor element 2 withstand voltage can be secured.

The protection voltage generation circuit 4 in the laser diode driving apparatus according to the first embodiment generates a control voltage for the protection circuit 3 so that the withstand voltage of the current driving circuit 2 can be secured when the laser diode 5 is not operated to emit light. Yes. The protection voltage generation circuit 4 generates a control voltage based on the control signal X from the variable current control line 6, and transmits the generated control voltage to the protection circuit 3.
On the other hand, when the laser diode 5 is in a light emitting operation, the protection voltage generation circuit 4 generates a control voltage that maximizes the anode voltage of the laser diode 5 in accordance with the control signal X from the variable current control line 6. In addition, a control voltage capable of normally operating the current driving circuit 2 and the protection circuit 3 is generated, and the generated control voltage is transmitted to the protection circuit 3.

Next, a specific circuit configuration example of the laser diode driving apparatus according to the first embodiment shown in the block diagram of FIG. 1 will be described with reference to FIG.
The variable current source 1 can adjust the current by the control signal X of the variable current control line 6, and the current set by the variable current source 1 constitutes a current driving circuit 2 connected to the power supply terminal 9. The laser diode 5 is driven via the transistor 31 constituting the protection circuit 3 by being transmitted to the mirror circuit constituted by the transistor 21 and the transistor 22.

  Further, the control signal X of the variable current control line 6 is input to the variable current circuit 43 of the protection voltage generation circuit 4. The protection voltage generation circuit 4 is configured by connecting a resistance connection body configured by connecting a resistor 41 and a resistor 42 in series, and a variable current circuit 43 in series. A connection point between the resistor 41 and the resistor 42 serves as an output terminal of the protection voltage generation circuit 4 and is connected to the gate terminal of the transistor 31.

  When the laser diode 5 is not operated to emit light, the withstand voltage of the transistor 22 of the current drive circuit 2 is ensured by the transistor 31 of the protection circuit 3. The gate voltage of the transistor 31 of the protection circuit 3 is generated at the connection point of the resistor connection body in which the resistor 41 and the resistor 42 are connected in series in the protection voltage generation circuit 4. This gate voltage is adjusted by the variable current circuit 43 in the protection voltage generation circuit 4 so as to have a voltage value that can ensure the breakdown voltage of the transistor 22 and the transistor 31.

  On the other hand, when the laser diode 5 is caused to emit light, the gate voltage of the transistor 31 of the protection circuit 3 becomes a voltage at which the anode voltage of the laser diode 5 becomes maximum, and the transistors 22 and 31 can operate normally within the breakdown voltage. The voltage is adjusted by the variable current circuit 43 in the protection voltage generation circuit 4 so as to be a voltage. The protection voltage generation circuit 4 having the variable current circuit 43 controls the gate voltage of the transistor 31 based on the control signal X of the variable current control line 6 so that the laser diode 5 does not perform the light emission operation and the light emission operation. Can be selected. Therefore, when the laser diode 5 is not operated to emit light, the variable current circuit 43 controlled by the control signal X from the variable current control line 6 ensures the breakdown voltage of each component.

  As described above, in the laser diode driving apparatus according to the first embodiment, the laser diode 5 is switched by switching the control voltage from the protection voltage generation circuit 4 to the protection circuit 3 in accordance with the state of the current flowing through the laser diode 5. Even when the light emitting operation is not performed, the breakdown voltage of each component can be ensured. In the laser diode driving apparatus according to the first embodiment, a configuration capable of driving a laser diode having a high operating voltage, such as a short-wavelength laser diode, even when a circuit is configured using a low-breakdown-voltage semiconductor element. It becomes.

  In the laser diode driving apparatus according to the first embodiment shown in FIGS. 1 and 2, the driving of the cathode common type laser diode 5 has been described. However, according to the configuration shown in FIGS. 3 and 4, the anode common type is used. The same effect can be obtained in driving the laser diode 5. FIG. 3 is a block diagram showing a configuration of a laser diode driving apparatus using the anode common type laser diode 5. FIG. 4 is a circuit diagram showing a specific configuration example of the laser diode driving device shown in FIG. The configuration and operation of the laser diode driving device shown in FIGS. 3 and 4 are substantially the same as those of the laser diode driving device shown in FIGS. 1 and 2 described above, and therefore the description thereof is omitted here.

  In the laser diode driving apparatus of the first embodiment, as shown in FIG. 2, the transistor element of the constituent circuit has been described as a P-channel FET. However, a PNP transistor may be used, and the same effect can be obtained. In the laser diode driving device shown in FIG. 4, the transistor elements of the constituent circuits are shown as N-channel FETs. However, NPN transistors may be used, and the same effect is obtained.

  Next, a laser diode driving apparatus according to a second embodiment of the present invention will be described with reference to FIGS. 5 and 6. FIG. 5 is a block diagram showing a configuration of the laser diode driving apparatus of the second embodiment, and FIG. 6 is an example of a specific circuit configuration of the laser diode driving apparatus shown in FIG.

  As shown in FIG. 5, the laser diode driving apparatus according to the second embodiment amplifies the variable current source 1 that can adjust the current for driving the laser diode 5 and the output current of the variable current source 1. A current driving circuit 2 capable of generating a current, and a protection circuit 3 that operates to ensure the withstand voltage of the current driving circuit 2 when the laser diode 5 is not operated to emit light, and that transmits an output current of the current driving circuit 2 to the laser diode 5; The anode is connected to the output of the protection circuit 3, the cathode is grounded, and the voltage on the anode side of the laser diode 5 is input, and the operating voltage of the laser diode 5 is detected and the status signal Y is output. The operating state of the laser operating voltage detecting circuit 7 which is the operating detecting means to output and the laser diode 5 obtained from the laser operating voltage detecting circuit 7 is shown. Based on the status signals Y, configured to include a protective voltage generating circuit 4 for transmitting and generates a control voltage that can secure the withstand voltage of the current drive circuit 2 and the protection circuit 3 to the protection circuit 3, a. In the protection voltage generation circuit 4, when the laser diode 5 is not operated to emit light based on the state signal Y, the protection voltage generation circuit 4 outputs to the protection circuit 3 a control voltage that can ensure the withstand voltage of the current drive circuit 2 and the protection circuit 3. When the light emission operation is performed, a control voltage set in advance so as to maximize the anode voltage of the laser diode 5 is output to the protection circuit 3.

  The laser diode driving device according to the second embodiment is different from the laser diode driving device according to the first embodiment in that a laser operating voltage detection circuit 7 is provided, and the protection voltage generation circuit 4 is changed from the laser operating voltage detection circuit 7. The control signal is generated and transmitted to the protection circuit 3 by the state signal Y.

The operation of the laser diode driving apparatus of the second embodiment configured as described above will be described below.
In the laser diode driving apparatus according to the second embodiment, the variable current source 1 can adjust the current flowing through the laser diode 5, and the adjustment operation is controlled by a control signal X input to the variable current source 1. ing. Thus, the variable current source 1 can adjust the light emission power of the laser diode 5 according to the control signal X input from the variable current control line 6. Therefore, the control signal X is a signal that indirectly indicates the light emission operation state that is the operation state of the laser diode 5.

  The current determined in the variable current source 1 to which the control signal X is input is transmitted to the current driving circuit 2. The current drive circuit 2 can amplify and output the transmitted current, and the amplified output current drives the laser diode 5 through the protection circuit 3. In the laser diode driving apparatus of the second embodiment, since the protection circuit 3 is provided, the output voltage of the current driving circuit 2 is fixed (determined) by the output voltage of the protection circuit 3 and the laser diode 5 is not operated to emit light. The withstand voltage of the current drive circuit 2 is ensured.

  In the laser diode driving apparatus of the second embodiment configured as described above, if the protection circuit 3 is not provided, the output of the current driving circuit 2 and the anode of the laser diode 5 are directly connected. Become. In the case of such a configuration, when the laser diode 5 is not operated to emit light, the anode voltage of the laser diode 5, that is, the output voltage of the current drive circuit 2 is a voltage substantially close to the GND potential. In the case where the power supply of the circuit to be operated is 8 to 10 V, there is a problem that the withstand voltage of the current drive circuit 2 cannot be secured if it is composed of low withstand voltage semiconductor elements.

  Therefore, in the laser diode driving apparatus of the second embodiment, the protection circuit 3, the protection voltage generation circuit 4, and the laser operating voltage detection circuit 7 are provided. For this reason, it becomes possible to fix (set) the output voltage of the current drive circuit 2 with the output voltage of the protection circuit 3, and to ensure the withstand voltage of the current drive circuit 2 when the laser diode 5 is not operated to emit light. .

  In the laser diode driving apparatus according to the second embodiment, the laser operating voltage detection circuit 7 that detects the operating voltage of the laser diode 5 can detect whether or not the laser diode 5 is in a light emitting operation state. A certain state signal Y is transmitted to the protection voltage generation circuit 4 through the laser operating voltage detection line 8.

  The protection voltage generation circuit 4 in the laser diode driving apparatus of the second embodiment generates a control voltage for the protection circuit 3 so that the withstand voltage of the current driving circuit 2 can be secured when the laser diode 5 is not operated to emit light. Yes. The protection voltage generation circuit 4 generates a control voltage corresponding to the state signal Y from the laser operating voltage detection line 8 and transmits the generated control voltage to the protection circuit 3.

  On the other hand, when the laser diode 5 is operating to emit light, the protection voltage generation circuit 4 generates a control voltage that maximizes the anode voltage of the laser diode 5 in accordance with the status signal Y from the laser operating voltage detection line 8. In addition, a control voltage capable of normally operating the current driving circuit 2 and the protection circuit 3 is generated, and the generated control voltage is transmitted to the protection circuit 3.

Next, a specific circuit configuration example of the laser diode driving apparatus according to the second embodiment shown in the block diagram of FIG. 5 will be described with reference to FIG.
The variable current source 1 can adjust the current by the control signal X of the variable current control line 6, and the current set by the variable current source 1 constitutes a current driving circuit 2 connected to the power supply terminal 9. The laser diode 5 is driven via the transistor 31 constituting the protection circuit 3 by being transmitted to the mirror circuit constituted by the transistor 21 and the transistor 22.

  When the laser diode 5 is not operated to emit light, the withstand voltage of the transistor 22 of the current drive circuit 2 is ensured by the transistor 31 of the protection circuit 3. The gate voltage of the transistor 31 of the protection circuit 3 is generated at the connection point of the resistor connection body in which the resistor 41 and the resistor 42 are connected in series in the protection voltage generation circuit 4. This gate voltage is adjusted by the variable current circuit 43 in the protection voltage generation circuit 4 so as to have a voltage value that can ensure the breakdown voltage of the transistor 22 and the transistor 31.

  On the other hand, when the laser diode 5 is caused to emit light, the gate voltage of the transistor 31 of the protection circuit 3 is a voltage at which the anode voltage of the laser diode 5 is maximized, and a voltage at which the transistors 22 and 31 can operate normally. As described above, the adjustment is made by the variable current circuit 43 in the protection voltage generation circuit 4. The status signal Y from the laser operating voltage detection circuit 8 is transmitted to the variable current circuit 43 of the protection voltage generation circuit 4 via the laser operation voltage detection line 8, and the protection voltage generation circuit 4 generates a control voltage for the protection circuit 3. And transmitted to the protection circuit 3.

  As shown in FIG. 6, the laser operating voltage detection circuit 7 includes a series connection body of a resistor 71 and a resistor 72 connected in series between the anode of the laser diode 5 and GND, and a comparator 74. A connection point between the resistors 71 and 72 is connected to one input terminal of the comparator 74, and a variable voltage circuit 73 is connected to the other input terminal of the comparator 74. The voltage output from the variable voltage circuit 73 is set to a voltage that becomes a threshold value for identifying whether or not the laser diode 5 is emitting light. The state signal Y that is the output of the comparator 74 is transmitted to the variable current circuit 43 of the protection voltage generation circuit 4 via the laser operating voltage detection line 8. Therefore, it is possible to reliably detect whether the laser diode 5 is in a light emitting operation state or not in a light emitting operation state based on the state signal Y output from the laser operating voltage detection circuit 7. It is.

  As described above, in the laser diode driving apparatus according to the second embodiment, the laser operating voltage detection circuit 7 detects the operating state of the laser diode 5 to generate the state signal Y, and the protection voltage generation circuit 4 has the laser operating voltage detection circuit. 7, the gate voltage of the transistor 31 is controlled by switching the amount of current of the variable current circuit 43 based on the state signal Y from 7 to select whether the laser diode 5 does not perform the light emission operation or when the laser diode 5 performs the light emission operation. be able to. For this reason, when the laser diode 5 is not operated to emit light, the breakdown voltage of each component element is reliably ensured.

  As described above, in the laser diode driving apparatus according to the second embodiment, the operating voltage indicating the operating state of the laser diode 5 is detected, and the protection voltage generating circuit 4 is controlled according to the detected operating state of the laser diode 5. By switching the voltage, the breakdown voltage of each component can be reliably ensured even when the laser diode 5 is not emitting light. In the laser diode driving apparatus according to the second embodiment, a configuration capable of driving a laser diode having a high operating voltage, such as a laser diode having a short wavelength, even when a circuit is configured by using a low breakdown voltage semiconductor element. It becomes.

  In the laser diode driving apparatus of the second embodiment shown in FIGS. 5 and 6, the driving of the cathode common type laser diode 5 has been described. However, according to the configuration shown in FIGS. The same effect can be obtained in driving the laser diode 5. FIG. 7 is a block diagram showing a configuration of a laser diode driving device using the anode common type laser diode 5. FIG. 8 is a circuit diagram showing a specific configuration example of the laser diode driving device shown in FIG. Since the configuration and operation of the laser diode driving device shown in FIGS. 7 and 8 are substantially the same as those of the laser diode driving device shown in FIGS. 5 and 6, the description thereof is omitted here.

  In the laser diode driving apparatus of the second embodiment, as shown in FIG. 6, the transistor element of the constituent circuit has been described as a P-channel FET. However, a PNP transistor may be used, and the same effect can be obtained. In the laser diode driving apparatus shown in FIG. 8, the transistor elements of the constituent circuits are shown as N-channel FETs. However, NPN transistors may be used, and the same effect is obtained.

  In the laser diode driving device of the present invention, the control signal X input to the variable current source 1 described in the first embodiment and the laser diode described in the second embodiment are used as signals indicating the operating state of the laser diode. It is also possible to select both signals of the state signal Y obtained from the operating voltage or one of the signals to generate an appropriate control voltage for the protection circuit 3. With this configuration, it is possible to provide a highly versatile laser diode driving device that can support various specifications.

  In the present invention, as the operation detecting means for detecting the operating state of the laser diode, for example, in the first embodiment, the control signal X that indirectly indicates the operating state of the laser diode is supplied to the protection voltage generating circuit 4 through the variable current control line 6. And a status signal Y directly indicating the operating state of the laser diode in the second embodiment is generated by the laser operating voltage detection circuit 7, and the laser operating voltage detection line 8 is connected to the protection voltage generating circuit 4. The configuration input via is included.

  As described above, as described in the above embodiments, in the present invention, even when the laser diode is not operated to emit light, a breakdown voltage for preventing dielectric breakdown of the circuit element that drives the laser diode is secured. However, it is possible to reduce the idling current by preventing minute emission of the laser diode. In addition, the laser diode drive device of the present invention is miniaturized because the breakdown voltage of the protection circuit and the current drive circuit is secured by the voltage set by the protection voltage generation circuit when the laser diode is not operated to emit light. A low-breakdown-voltage semiconductor element having a structure can be used for a laser diode driving device.

  The present invention is not limited to the configurations of the above-described embodiments, and various modifications based on the same technical idea are possible, and those modified configurations are also included in the scope of the present invention. Needless to say.

  Since the laser diode driving device of the present invention has excellent effects such as reduction of power consumption and deterioration of the laser diode while ensuring a breakdown voltage for a miniaturized low breakdown voltage semiconductor element, It is useful for products in a wide range of fields such as information recording / reproducing field, information communication field, and office equipment field.

DESCRIPTION OF SYMBOLS 1 Variable current source 2 Current drive circuit 3 Protection circuit 4 Protection voltage generation circuit 5 Laser diode 6 Variable current control line 7 Laser operation voltage detection circuit 8 Laser operation voltage detection line 9 Power supply terminal 21 Transistor 22 Transistor 31 Transistor 41 Resistance 42 Resistance 43 Variable current circuit 71 Resistor 72 Resistor 73 Variable voltage circuit 74 Comparator

Claims (8)

A laser diode driving device for driving a laser diode by a current driving circuit,
A protection circuit for outputting a voltage for fixing the output of the current driving circuit;
An operation detecting means for detecting an operating state of the laser diode;
A control voltage generation circuit for determining a control voltage input to the protection circuit according to a signal from the operation detection unit, and controlling an output voltage of the protection circuit interlocked with the control voltage;
The protection voltage generation circuit controls a control voltage to the protection circuit when the laser diode is not emitting light, so that a voltage applied to the current drive circuit is within a withstand voltage range of the current drive circuit. A laser diode drive configured to be set.   The laser diode driving apparatus according to claim 1, further comprising a variable current source that adjusts a current flowing through the laser diode and transmits the current to the current driving circuit.   The laser diode driving device according to claim 1, wherein the protection circuit generation circuit is configured to detect a control signal for controlling the variable current source and to control an output voltage of the protection circuit.   The laser diode driving apparatus according to claim 1, wherein the protection voltage generation circuit is configured to control an output voltage of the protection circuit based on an anode voltage of the laser diode.   3. The laser diode drive device according to claim 1, wherein the operation detection unit is configured to detect an operation state of the laser diode based on a control signal for adjusting a current flowing through the laser diode. 4. .   The operation detection means includes a comparator that compares a current corresponding to the current flowing through the laser diode with a threshold value, detects an operation state of the laser diode, and protects a state signal indicating the operation state The laser diode driving device according to claim 1, wherein the laser diode driving device is configured to output to a voltage generation circuit.   The laser diode is configured as a common cathode type, the protection circuit includes a P-channel FET, the gate of the FET is connected to the output of the protection voltage generation circuit, and the source of the FET is connected to the current drive circuit. 7. The laser diode driving device according to claim 1, wherein a drain of the FET is connected to an anode of the laser diode.   The laser diode is configured as an anode common type, the protection circuit includes an N-channel FET, a gate of the FET is connected to an output of the protection voltage generation circuit, and a source of the FET is connected to the current driving circuit. 7. The laser diode driving device according to claim 1, wherein a drain of the FET is connected to a cathode of the laser diode.

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