JP2005142449A - Laser driving device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a laser driving device which can operate a laser light emitting element reliably at power-on, and can protect the laser light emitting device when disconnection or the like occurs. <P>SOLUTION: The laser driving device comprises a monitor voltage monitoring circuit block C which is constituted of a second power element 4 for turning on/off an operating current I1 which lights the laser light emitting device of a semiconductor laser block A; and a comparator 5 which, when a monitor current I2 in accordance with an amount of emitted lights of the laser light emitting device is converted by a current-voltage converter 3 and the resultant monitor voltage Vmo is less than a minimum monitor voltage Vmin, outputs an output stop signal S2 which turns off the operating current I1 to the second power element 4, and also comprises a circuit which is caused to flow the operating current I1 so that the monitor voltage Vmo is equal to or more than the minimum monitor voltage Vmin. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

    The present invention relates to a laser driving device that maintains a light emission amount of a semiconductor laser at a predetermined value.

Conventionally, as this type of laser diode protection circuit, the laser output control circuit 103 is driven to the laser diode 102 by a detection signal corresponding to the light amount of the light beam output from the laser diode 102 obtained from the light amount detection diode 101. In the circuit configured to make the light quantity of the light beam output from the laser diode 102 constant by controlling the operation of the driving transistor 104 that supplies current, the detection signal from the light quantity detection diode 101 is For example, when a short circuit of a wiring pattern or a contact failure of a connector occurs and the laser output control circuit 103 is not input, a driving transistor that supplies a driving current to the laser diode 102 by bringing the control transistor 105 into a conductive state. 104 By changing the bias to the non-conducting direction, the laser diode 102 by excessive current flow through the laser diode 102 is provided which prevents the destruction (Patent Document 1).
JP-A-8-330656 (FIG. 1)

  The above-described laser diode protection circuit causes the driving transistor 104 to become non-conductive as described above when a detection signal cannot be obtained from the light quantity detection diode 101 due to an accident such as a short circuit in the wiring pattern or a poor contact of the connector. By interrupting the flow of the drive current of the laser diode 102, the laser diode 102 is protected from excessive supply of the drive current.

  However, if the detection signal cannot be obtained from the light quantity detection diode 101, the flow of the drive current is cut off. Even if the laser diode 102 immediately after the power is turned on, the light detection diode 101 also detects the detection signal. Cannot be obtained, and thus the operation target of the protection circuit described above is obtained.

  In such a case, when the above-described protection circuit operates, the flow of the drive current of the laser diode 102 is interrupted despite the occurrence of an accident such as a short circuit of the wiring pattern or a poor contact of the collector, and the laser diode 102 Cannot be emitted.

  Therefore, such a laser diode protection circuit is set so as not to malfunction as described above in the initial operation when the power is turned on, but since this operation setting is complicated, the initial operation is unstable, There was a problem of lack of certainty of operation.

  The present invention has been made in view of the above points, and an object of the present invention is to provide a laser driving apparatus that can reliably operate the light emitting element when the power is turned on and can protect the light emitting element when a disconnection or the like occurs. Is to provide.

  In order to solve the above problems, in the invention of claim 1, a semiconductor laser block comprising a laser light emitting element and a light receiving element that receives light emitted from the laser light emitting element and outputs a current corresponding to the amount of light emitted. A first power element connected in series with the laser light-emitting element and energized with an operating current for causing the laser light-emitting element to emit light, and a current-voltage converter that converts the current from the light-receiving element into a voltage, And a light quantity control element unit that outputs a control signal for controlling the first power element so that the voltage converted by the current-voltage conversion unit matches a predetermined reference voltage. A drive control circuit block, a second power element connected in series with the first power element, and for turning on and off the operation current passing through the first power element; and the current − The voltage converted by the voltage converter is compared with the minimum monitor voltage that is a criterion for determining whether or not the current path of the current output from the light receiving element is disconnected, and is converted by the current-voltage converter. A monitor voltage monitoring circuit block comprising a comparator for outputting an output stop signal for turning off the second power element when the detected voltage is less than the minimum monitor voltage, and conversion by the current-voltage converter And a circuit section for supplying an operating current for causing the laser light emitting element to emit light so that the measured voltage becomes equal to or higher than the minimum monitor voltage.

  According to the first aspect of the present invention, the voltage obtained by converting the current obtained by the light receiving element according to the light emission amount of the laser light emitting element by the current-voltage conversion unit is compared with the minimum monitor voltage, and the current -When the voltage converted by the voltage converter is less than the minimum monitor voltage, the monitor voltage monitoring circuit block that cuts off the flow of the operating current that causes the laser light emitting element to emit light is provided. In some cases, it is possible to prevent an excessive output of the laser light emitting element, which is caused when the light amount control element unit increases the light emission amount of the laser light emitting element. In addition, since it has a circuit section for supplying an operating current for causing the laser light emitting element to emit light so that the voltage converted by the current-voltage conversion section is equal to or higher than the minimum monitor voltage, immediately after turning on the power supply The laser light emitting element can be turned on even if the function of the monitor voltage monitoring circuit block described above is activated.

  According to a second aspect of the present invention, in addition to the configuration of the first aspect of the invention, the circuit section operates with the laser drive control circuit block until the laser light emitting element emits light. A driving device was used.

  According to the second aspect of the present invention, the laser light emitting element emits light in the circuit section for supplying an operating current for causing the laser light emitting element to emit light so that the voltage converted by the current-voltage conversion section is equal to or higher than the minimum monitor voltage. In the meantime, since it operates with the laser drive control circuit block, power saving can be achieved in addition to the effect of the invention of the first aspect.

  According to a third aspect of the present invention, in addition to the configuration of the first or second aspect of the present invention, the circuit section includes at least a bypass circuit connected in parallel to the second power element and bypassing the operating current. It was set as the characteristic laser drive device.

  According to a third aspect of the present invention, at least the second power element includes a circuit section for supplying an operating current for causing the laser light emitting element to emit light so that the voltage converted by the current-voltage conversion section is equal to or higher than the minimum monitor voltage. By providing a bypass circuit that is connected in parallel to bypass the operating current, the same effect as that of the first aspect of the invention can be obtained.

  According to a fourth aspect of the present invention, in addition to the configuration of the first aspect of the invention, the circuit unit includes a forced on circuit that turns on the second power element for a certain period of time after power-on and the second power element. The laser drive device is characterized by this.

  According to the fourth aspect of the present invention, the circuit unit for supplying the operating current for causing the laser light emitting element to emit light so that the voltage converted by the current-voltage conversion unit is equal to or higher than the minimum monitor voltage is provided for a certain period of time after the power is turned on. Since the second power element is constituted by the forced on circuit that turns on the second power element, the effect similar to the effect of the invention of claim 1 can be obtained.

  The voltage obtained by converting the current obtained by the light receiving element according to the light emission amount of the laser light emitting element by the current-voltage conversion unit and the minimum monitor voltage, and the voltage converted by the current-voltage conversion unit Is provided with a monitor voltage monitoring circuit block that cuts off the flow of the operating current that causes the laser light emitting element to emit light when the laser power is less than the minimum monitor voltage. It is possible to prevent an excessive output of the laser light-emitting element caused by increasing the light emission amount of the light-emitting element. In addition, since it has a circuit section for supplying an operating current for causing the laser light emitting element to emit light so that the voltage converted by the current-voltage conversion section is equal to or higher than the minimum monitor voltage, immediately after turning on the power supply The laser light emitting element can be turned on even if the function of the monitor voltage monitoring circuit block described above is activated.

  As shown in FIG. 1, the laser drive device of the present invention mainly includes a semiconductor laser block A, a laser drive control circuit block comprising a first power element 1, a light quantity control element section 2, and a current-voltage conversion section 3. B, a monitor voltage monitoring circuit block C composed of the second power element 4 and the comparison unit 5, and a circuit unit (not shown) for reliably operating the semiconductor laser block A.

  The semiconductor laser block A has a laser light-emitting element and a light-receiving element that receives light emitted from the laser light-emitting element and outputs a current corresponding to the light emission amount. The laser light-emitting element emits light and emits light. The operating current I1 that changes the power is supplied to a series circuit composed of the first power element 1 and the second power element 4. Further, the monitor current I2 that is the current output from the light receiving element is converted into a voltage by the current-voltage converter 3 to be a monitor voltage Vmo. The light quantity control element unit 2 outputs a control signal S1 that controls the first power element 1 and changes the energization amount of the operating current I1 so that the monitor voltage Vmo matches the predetermined reference voltage Vst. To do.

  At this time, the comparison unit 5 compares the monitor voltage Vmo with the minimum monitor voltage Vmin set as a criterion for determining whether or not the conducting path of the monitor current I2 is disconnected, and the monitor voltage Vmo is the minimum monitor voltage Vmin. If it is less, the second power element 4 is controlled to output an output stop signal S2 for cutting off the operation current I1. As described above, when disconnection occurs in the energization path of the monitor current I2, the operation of interrupting the energization path of the operating current I1 is shown.

  As a result, when the monitor voltage Vmo is disconnected due to the disconnection of the monitor current I2 and the light amount control element unit 2 increases the monitor voltage Vmo, the operating current I1 is supplied to the first power element 1. By instructing to increase the energization amount of the laser, it is possible to prevent a problem that the laser output from the semiconductor laser block A becomes excessive in output.

  The embodiments of the laser driving device will be described below with reference to FIGS.

(Embodiment 1)
FIG. 2 shows a circuit diagram of the laser driving apparatus according to the first embodiment of the present invention. The semiconductor laser block A is composed of a laser diode 6 which is a light emitting element for laser and a photodiode 7 which is a light receiving element, and both the anode of the laser diode 6 and the cathode of the photodiode 7 are connected to a power source Vcc. .

  The cathode of the laser diode 6 is connected to the ground via a series circuit composed of first and second power elements 1 and 4 each composed of a power transistor. In this series circuit, a bypass circuit including a resistor R5 that bypasses the operating current I1 of the laser diode 6 is formed.

  The anode of the photodiode 7 is connected to the ground via a resistor R8 that constitutes the current-voltage converter 3. The photodiode 7 and the resistor R8 are connected to one input unit of the light quantity control element unit 2 made of an operational amplifier and one input unit of the comparison unit 5 made of a comparator.

The other input part of the light quantity control element part 2 is connected between resistors R3 and R7 of a reference voltage circuit 8 described later, and the output part of the light quantity control element part 2 is connected to the first power element 1 via the resistor R4. Connected with the base. The reference voltage circuit 8, a reference power supply V ₀ is formed by connecting a variable resistor VR, and the ground through a series circuit comprising resistors R3, R7, variable resistor VR, and by the resistance R3, R7 reference by dividing the power source _{V 0,} which generates a reference voltage Vst in between the resistors R3, R7.

  The other input unit of the comparison unit 5 is connected between the resistors R2 and R6 of the series circuit including the resistors R2 and R6 that connect the power source Vcc to the ground, and the output unit of the comparison unit 5 supplies the power source Vcc to the second power. The resistor 4 is connected between resistors R1 and R9 of a series circuit including resistors R1 and R9 connected to the base of the element 4. The series circuit composed of the resistors R2 and R6 divides the power supply Vcc and generates a minimum monitor voltage Vmin between the resistors R2 and R6.

  As described above, the laser driving device of the present embodiment is configured, and the operation thereof will be described below using the timing chart shown in FIG.

  When the power supply Vcc is turned on, the operating current I1 for causing the laser diode 6 to emit light starts to flow, the current value rises as shown in FIG. 3A, and the laser diode 6 emits light eventually. The photodiode 7 receives this light emission and outputs a monitor current I2 that is a current corresponding to the amount of light emission. The output monitor current I2 is converted to the monitor voltage Vmo by the current-voltage conversion unit 3 and input to the light quantity control element unit 2 and the comparison unit 5.

  The light quantity control element unit 2 controls the energization amount of the operating current I1 that energizes the first power element 1 so that the reference voltage Vst generated as described above and the predefined reference voltage Vst coincide with the monitor voltage Vmo. The signal S1 is output, and the control signal S1 is energized to the base of the first power element 1. Eventually, the operating current I1 becomes constant as shown in FIG. 3 (a), whereby the monitor voltage Vmo can be made to coincide with the reference voltage Vst defined in advance as shown in FIG. 3 (b).

  The comparison unit 5 compares the monitor voltage Vmo with the minimum monitor voltage Vmin that is generated as described above and serves as a criterion for determining whether or not the energization path of the monitor current I2 is disconnected, and the monitor voltage Vmo is the minimum monitor voltage. An output stop signal which is an L level control signal Sc as shown in FIG. 3C in order to cut off the flow of the operating current I1 energized on the second power element 4 when it becomes less than Vmin. S <b> 2 is output and the output stop signal S <b> 2 is energized to the base of the second power element 4.

  This operation should be performed only when a disconnection occurs in the energization path of the monitor current I2, which will be described later, but immediately after the power supply Vcc is turned on, the light emission amount of the laser diode 6 is small, as shown in FIG. Before the time t1 shown, the monitor voltage Vmo falls below the minimum monitor voltage Vmin, so that the output stop signal S2 shown in FIG. 3C is output. As a result, the second power element 4 cuts off the supply of the operating current I1, so that the operating current I1 does not pass through the laser diode 6, and the laser diode 6 cannot emit light.

  Therefore, in the present embodiment, the circuit section is constituted by a bypass circuit that bypasses the operating current I1 to the laser diode 6, and is connected as described above. The resistor R5 provided in the bypass circuit is set to a resistance value at which the operating current I1 at which the monitor voltage Vmo is at least the minimum monitor voltage Vmin can be passed. Therefore, even when the output stop signal S2 is output from the comparison unit 5 as described above, the laser diode 6 can emit light so that the light emission amount is at least the minimum monitor voltage Vmin.

  As described above, the laser driving device according to the present embodiment has an effect of keeping the light emission amount of the laser output from the semiconductor laser block A constant by the laser driving control circuit block B if there is no abnormality.

  Next, the operation when the current path for the monitor current I2 is disconnected will be described with reference to the timing chart shown in FIG. 4A is a timing chart of the operating current I1, FIG. 4B is a timing chart of the monitor voltage Vmo, and FIG. 4C is a timing chart of the control signal Sc output from the comparison unit 5. Also, time t2 shown in FIG. 4 is the time when the disconnection occurs.

  Before the time t2 when the disconnection occurs, the monitor voltage Vmo exceeds the minimum monitor voltage Vmin as shown in FIG. 4B, and the control signal Sc of H level shown in FIG. Thus, the operating current I1 flows at a value determined by the light quantity control element unit 2 as shown in FIG. Thereafter, at time t2, since the disconnection has occurred, the monitor voltage Vmo rapidly decreases and falls below the minimum monitor voltage Vmin as shown in FIG. 4B. An output stop signal S2, which is a control signal Sc, is output. In accordance with this output stop signal S2, the second power element 4 cuts off the operating current I1, and the operating current I1 passes only through the bypass circuit described above. It decreases as shown in FIG.

  According to the present embodiment, the amount of laser light emitted from the laser diode 6 is detected by the photodiode 7 as the monitor current I2, and the monitor current I2 is converted to the monitor voltage Vmo using the resistor R8. When the monitor power Vmo is lower than the minimum monitor voltage Vmin by comparing with the minimum monitor voltage Vmin, the flow of the operating current I1 is cut off, and the light emission amount of the laser diode 6 is reduced to a very low light emission amount by the resistor R5. Can be made. Therefore, it is possible to prevent the output of the laser diode 6 from being excessive when the light quantity control element unit 2 attempts to increase the light emission amount of the laser diode 6 when disconnection or the like occurs.

  Since the laser diode 6 is connected to the bypass circuit having the resistor R5 in addition to the series circuit composed of the power elements 1 and 4, the function of the monitor voltage monitoring circuit block C described above immediately after the power supply Vcc is turned on. Even if is activated, the laser diode 6 can be turned on. In this case, if the power supply Vcc is on, the laser diode 6 is always turned on, but the resistance value of the resistor R5 is set so that only the operating current I1 exceeding the minimum monitor voltage Vmin flows through the laser diode 6. Therefore, the laser diode 6 is lit with a very low light amount. Therefore, it hardly affects the operation of the laser drive circuit control block B described above.

(Embodiment 2)
In the first embodiment described above, the resistor R5 is disposed on the bypass circuit parallel to the series circuit composed of the two power elements 1 and 4 connected to the laser diode 6, but in this embodiment, the resistor R5 is shown in FIG. As described above, the second power element 4 is arranged on a bypass circuit parallel only to the second power element 4, and the other configurations are the same as those of the first embodiment, and thus the description thereof is omitted.

  Here, the relationship between the operating current I1 and the reference voltage Vst when the second power element 4 is in a state where the flow of the operating current I1 is blocked by the output stop signal S2 will be described with reference to FIG. FIG. 6A is a timing chart of the reference voltage Vst, and FIG. 6B is a timing chart of the operating current I1.

Operating current I1 and the reference voltage Vst is, for example, a reference power supply V ₀ at time t3 shown in FIG. 6 becomes reduced initially, 0 both at time t4 turns off. When turning on the reference supply V ₀ at time t4, indicating the behavior of the operating current I1 and the reference voltage Vst both increased initially, back to the value before decreasing at time t5. That is, the first power element 1 can be turned off by turning off the reference power source V _{0 and} setting the reference voltage Vst to 0V. As a result, the energization of the operating current I1 can be cut off.

  According to the present embodiment, the following effects can be obtained in addition to the effects of the first embodiment. That is, in the above-described first embodiment, the bypass circuit having the resistor R5 is connected to the laser diode 6 in parallel with both the power elements 1 and 4, so that the laser diode that is always lit when the power supply Vcc is on. In this embodiment, since the bypass circuit having the resistor R5 is connected to the laser diode 6 only in parallel with the second power element 4, the reference voltage Vst is set to 0 V as described above and the first power element 4 is connected. By turning off the power element 1, the flow of the operating current I1 to the laser diode 6 can be cut off, the laser diode 6 can be turned off, and current consumption can be suppressed. Thereby, not only can the power supply Vcc be turned on and the laser diode 6 can be turned on, but also after the power supply Vcc is turned on, the laser diode 6 can be turned on arbitrarily without being turned on and turned off. .

(Embodiment 3)
In the present embodiment, instead of the bypass circuit having the resistor R5 described in the first embodiment, as shown in FIG. 7, a forced on circuit 9 composed of a time constant circuit including a capacitor 10 and a resistor R5 is used as a power source. Connected between Vcc and the base of the second power element 4, the forced ON circuit 9 and the second power element 4 emit the laser diode 6 so that the monitor voltage Vmo is equal to or higher than the minimum monitor voltage Vmin. The circuit part which supplies the operating current I1 to make is comprised. Other configurations are almost the same as those of the first embodiment, and the description thereof is omitted.

  Next, the operation of the laser driving device of this embodiment will be described with reference to FIG. 8A is a timing chart of the base voltage Vb applied to the base of the second power element 4, FIG. 8B is a timing chart of the monitor voltage Vmo, and FIG. 8C is a timing chart of the control signal Sc output from the comparison unit 5. A timing chart is shown.

  Immediately after the power supply Vcc is turned on, the monitor voltage Vmo is lower than the minimum monitor voltage Vmin as shown in FIG. 8B, so that the control signal Sc is at the L level as shown in FIG. 8C. is there. Therefore, in Embodiment 1 described above, the second power element 4 is turned off with no voltage applied to the base. However, in this embodiment, since the forced on circuit 9 is provided, the voltage from the power supply Vcc is second. As shown in FIG. 8A, the base voltage Vb rises and the operating current I1 can be applied. In this way, the laser diode 6 is turned on. Eventually, as shown in FIG. 8B, the monitor voltage Vmo exceeds the minimum monitor voltage Vmin at time t6, and the control signal Sc is changed to that shown in FIG. 8C at time t7. As shown, the second power element 4 is held in the ON state. Further, the base voltage Vb decreases as shown in FIG. 8 (a) until it reaches the time t7 after showing the peak immediately before the time t6. This is the capacitor provided in the forced-on circuit 9. This is because 10 is charged.

  According to the present embodiment, even if the output stop signal S2, which is the L level control signal Sc, is output from the comparison unit 5, the forced on circuit that turns on the second power element 4 for a certain period of time after the power source Vcc is turned on. Since 9 is provided, substantially the same effects as those of the first and second embodiments can be obtained.

It is a block diagram of the laser drive device of this invention. It is a circuit diagram of the laser drive device of Embodiment 1 of the present invention. (A) is a timing chart of the operating current I1, (b) is a timing chart of the monitor voltage Vmo, and (c) is a timing chart of the control signal Sc. (A) is a timing chart of the operating current I1, (b) is a timing chart of the monitor voltage Vmo, and (c) is a timing chart of the control signal Sc. It is a circuit diagram of the laser drive device of Embodiment 2 of the present invention. (A) is a timing chart of the reference voltage Vst, and (b) is a timing chart of the operating current I1. It is a circuit diagram of the laser drive device of Embodiment 3 of this invention. (A) is a timing chart of the base voltage Vb of the second power element, (b) is a timing chart of the monitor voltage Vmo, and (c) is a timing chart of the control signal Sc. It is a circuit diagram of the conventional laser drive device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 1st power element 2 Light quantity control element part 3 Current-voltage conversion part 4 2nd power element 5 Comparison part A Semiconductor laser block B Laser drive control circuit block C Monitor voltage monitoring circuit block I1 Operating current I2 Monitor current S1 Control Signal S2 Output stop signal Vst Reference voltage Vmo Monitor voltage Vmin Minimum monitor voltage

Claims (4)

  A semiconductor laser block comprising: a laser light emitting element; and a light receiving element that receives light emitted from the laser light emitting element and outputs a current corresponding to the light emission amount; and is connected in series with the laser light emitting element. A first power element that supplies an operating current for causing the light emitting element to emit light, a current-voltage conversion unit that converts the current from the light receiving element into a voltage, and a voltage converted by the current-voltage conversion unit are defined in advance. A laser drive control circuit block including a light amount control element unit that outputs a control signal for controlling the first power element, and is connected in series with the first power element so that the reference voltage matches A second power element that turns on / off the operation current passing through the first power element, a voltage converted by the current-voltage converter, and a light output from the light receiving element. The current monitor is compared with a minimum monitor voltage, which is a criterion for determining whether or not the current flow path is disconnected, and the voltage converted by the current-voltage converter is less than the minimum monitor voltage. A monitor voltage monitoring circuit block comprising a comparator for outputting an output stop signal for turning off the two power elements, and the laser so that the voltage converted by the current-voltage converter is not less than the minimum monitor voltage. And a circuit section for supplying an operating current for causing the light emitting element to emit light.   The laser driving apparatus according to claim 1, wherein the circuit unit operates together with the laser driving control circuit block until the laser light emitting element emits light.   3. The laser driving device according to claim 1, wherein the circuit unit includes a bypass circuit that is connected in parallel to at least the second power element and bypasses the operating current. 4.   2. The laser driving apparatus according to claim 1, wherein the circuit unit includes a forced-on circuit that turns on the second power element for a predetermined time from power-on and the second power element.

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