JP2008112950A - Lasar diode luminescent circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a laser diode luminescent circuit capable of limiting excessive light by DC driving of a laser diode and suppressing excessive current to achieve stable operation when a photodiode detection signal ceases. <P>SOLUTION: The laser diode luminescent circuit consists of: a driving circuit unit comprising a first NPN transistor connected to a laser diode, a first operational amplifier for driving the transistor, a first reference voltage, a current detecting resistor, and two resistance dividing circuits disposed between output of the first operational amplifier and input of the first NPN transistor; a photodiode signal amplifying circuit unit; a first comparison deciding unit comprising a second operational amplifier for determining a comparison between output of the amplifying circuit unit and a second reference voltage in response to out of the amplifying circuit; and a second comparison deciding unit comprising a third operational amplifier for configuring an integrator. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

Detailed Description of the Invention

Industrial application fields

  The present invention relates to a light emitting circuit of a laser diode, and more particularly to a circuit for use in a laser pointer or the like that obtains stable light emission by direct current.

  FIG. 3 is a circuit diagram showing an example of a conventional laser diode light emitting circuit.

  FIG. 3 is a circuit described as a conventional example of Japanese Patent No. 2340667 (Japanese Patent Publication No. 08-031649), in which 1 is a laser diode, 2 is a photodiode for detecting the optical output of the laser diode, 3 is a pulse signal source, 4 Reference numeral 5 denotes a positive power source. The resistor 11 converts the signal of the photodiode 2 into a voltage. Reference numeral 6 denotes an operational amplifier, which inputs the difference between the voltage signal produced by the photodiode resistor 11 and the voltage produced by the duty comparator 7 and amplifies the difference to obtain the drive current of the laser diode 1. It has a configuration.

  In this conventional laser diode light emitting circuit, the output signal of the pulse signal source 3 is received by the duty comparator 7, and the AC signal with the pulse width obtained here is a reference signal for driving the laser diode 1. Therefore, the light emission amount is mainly determined by the pulse width, and the drive current has a pulsation peculiar to alternating current.

Problems to be solved by the invention

  The laser diode circuit described above uses a pulse signal generator as a reference voltage source and is driven by alternating current, so that there is a drawback that brightness pulsation occurs when this circuit is used as a laser pointer. Since the conventional circuit configuration is replaced with a DC drive circuit, a stable DC drive operation cannot be obtained even if the pulse signal generator 3 is replaced with a DC voltage source and the duty comparator 8 is replaced with a voltage comparator. Switching from conventional pulse width control to amplitude control requires that the amplitude be stable, and therefore detects abnormal conditions such as temperature changes at laser diode operating points and transient phenomena during light emission. However, a circuit that returns to the operation is necessary.

  An object of the present invention is to obtain a stable operation of a laser diode by direct current drive. Specifically, to provide a circuit that suppresses the drive current when excessive light output occurs and prevents the laser diode from being damaged by continuously increasing the laser diode drive current when the detection signal at the photodiode stops. It is in.

Means for solving the problem

  The present invention includes a laser diode, a first NPN transistor connected to the laser diode, a first operational amplifier that drives the transistor, a first reference voltage that is set at an input terminal of the operational amplifier, and the first A laser diode driving circuit unit (hereinafter referred to as a driving circuit) comprising a resistor connected to an NPN transistor and detecting a current, and two resistance dividing circuits located between the output of the first operational amplifier and the input of the first NPN transistor A photodiode that receives the light emitted from the laser diode, a photodiode signal amplifier circuit section that receives and amplifies and outputs the signal of the photodiode (hereinafter referred to as an amplifier circuit section), and an output of the amplifier circuit section A first comparison / determination circuit unit (hereinafter referred to as a first comparison / determination circuit unit) comprising a second operational amplifier for comparing and determining the magnitude of the second reference voltage. A second comparison / determination having a third operational amplifier that receives the output of the amplifier circuit and compares the magnitude with a third reference voltage and integrates and outputs the determined signal. Part (hereinafter referred to as a second comparison / determination circuit part).

  Next, the present invention will be described in detail with reference to the drawings. 1 and 2 are circuit diagrams showing an embodiment of the present invention.

  The laser diode 101 is connected to and driven by the first NPN transistor 102. A voltage is generated across the resistor 104 by the current that drives the laser diode 101, and this voltage is input to the operational amplifier 103 and compared with the first reference voltage. When the voltage is lower than the reference voltage, a higher voltage is output from the operational amplifier. This output voltage is voltage-divided by the resistors 501 and 502 and supplied to the base electrode of the first NPN transistor 102. When the voltage at both ends becomes equal to the first reference voltage value, the drive current of the laser diode 101 becomes constant. FIG. 1 shows a configuration in which the supply current to the laser diode 101 is limited by connecting the NPN transistor 202 of the limiting circuit unit to the connection point between the resistor 501 and the resistor 502. That is, in FIG. 1, when the current value supplied to the laser diode 101 is determined by the first reference voltage and an abnormality occurs in the optical signal monitored by the photodiode 107, the second NPN transistor 202 The base of one NPN transistor 102 is cut off. The photodiode 107 detects an optical signal of the laser diode 101 to be an electric signal, and becomes a voltage signal by the resistor 503. Since this signal is weak, it is once amplified by the amplifier circuit section. In FIG. 1 showing an embodiment of the present patent, a first comparison / determination circuit unit comprising a second operational amplifier 303 that receives the output voltage of the amplification circuit unit and compares and determines the magnitude of the output voltage with the second reference voltage. (Hereinafter referred to as a first comparison / determination circuit unit) and a third operational amplifier that receives the output of the amplifier circuit unit, compares the magnitude with a third reference voltage, and integrates and outputs the determined signal. And a second comparison / determination unit (hereinafter referred to as a second comparison / determination circuit unit). The time constant of the integrator for the second comparison / determination circuit is determined by the resistor 506 and the capacitor 601. The output of the first comparison / determination circuit unit and the output of the second comparison / determination circuit unit are wired-OR connected to become the input of the second NPN transistor 202. The NPN transistor 202 is the first of the drive circuit unit. It serves as a limiting circuit that outputs a control signal to the base of the NPN transistor. The NPN transistor 202 is in parallel with the resistor 502 of the driving circuit unit. When the NPN transistor 202 is completely turned on, the resistor 502 is short-circuited, that is, the driving voltage is 0 V, and the base of the NPN transistor 102 is cut off. The At this time, the resistor 501 prevents the output of the operational amplifier from directly grounding.

  In the present invention, two comparison / determination circuits, that is, two feedback systems in a steady state and a feedback system in an instantaneous state, are provided to stabilize the DC operation. The first comparison / determination circuit unit constitutes an instantaneous feedback system from the photodiode 107, and the second comparison / determination circuit unit constitutes a feedback system in a steady state. For example, an excessive voltage of the photodiode 107 is transmitted to the limiting circuit unit, the current of the driving circuit unit is limited by the NPN transistor 202, and at the same time, the disconnection of the photodiode 107 is detected by the second comparison / determination circuit unit. Normally, the disconnection state is irreversible, and is held once it occurs. Therefore, by delaying the output signal to the limiting circuit unit with an integrator, malfunction is less likely to occur. Since the signal of the photodiode 107 is usually a small signal and becomes extremely small at the time of disconnection, since the disconnection detection is easily buried in noise, the time-varying noise is removed by inserting an integrator, and the previous instantaneous Stable operation can be obtained in combination with a simple feedback system (first comparison / determination circuit).

  In the embodiment of the present invention shown in FIG. 2, the output of the first comparison / determination circuit unit and the output of the second comparison / determination circuit unit are divided by resistors 507 and 508 to obtain the first reference voltage of the drive circuit unit. To do. In the embodiment of FIG. 1, the maximum value of the drive current of the laser diode 101 is determined by the first reference voltage, but in FIG. 2, the maximum value of the drive current is determined by the output voltage values of the first and second comparison / determination circuit units. The value is determined. In a steady state, it is determined by the second comparison / determination unit, and the limitation during the transient phenomenon is performed by the first comparison / determination unit in principle in the same manner as the operation of FIG. In FIG. 1 and FIG. 2, Vcc is a power supply symbol for the operational amplifier.

The invention's effect

  As described above, the laser diode light emitting circuit of the present invention has two comparison / determination circuits, that is, a feedback system in a steady state and a feedback system in an instantaneous state. The system has an integrator to eliminate time-varying noise, and the drive circuit unit is limited to a single output from the previous instantaneous feedback system (first comparison / determination circuit). It is possible to obtain a stable operation. Further, in the embodiment of FIG. 1, the maximum current value is determined by the first reference voltage, and thus safe operation is ensured by setting this value within the safe operation range regardless of malfunction of the feedback system from the photodiode 107. There is an effect that can be done. The embodiment of FIG. 2 does not have this effect, but has the effect that the number of parts is smaller than that of FIG. 1. When the maximum current value is limited, the input terminal on the reference voltage side of the operational amplifier 103 and the ground By inserting a Zener diode between them, the same effect as in FIG. 1 can be obtained.

  It is a circuit diagram which shows one Example of the laser diode light emission circuit of this invention.   It is a circuit diagram which shows one Example of the laser diode light emission circuit of this invention.   It is a circuit diagram which shows an example of the conventional laser diode light emission circuit.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1,101 Laser diode 3 Pulse signal source 2,102,202 NPN transistor 6,103,203,303,403 Operation amplifier 104,501,502,503, Resistor 504,505,506,507,
508,11
7 Duty Comparator 107 Photodiode 12,601 Capacitor 4, 5,110 Positive Power Supply

Claims (3)

  A laser diode, a first NPN transistor connected to the laser diode, a first operational amplifier driving the transistor, a first reference voltage set at an input terminal of the operational amplifier, and the first NPN transistor A resistor for detecting a current, and a laser diode driving circuit unit (hereinafter referred to as a driving circuit unit) comprising two resistance dividing circuits located between the output of the first operational amplifier and the input of the first NPN transistor; A photodiode that receives light emitted from the laser diode, a photodiode signal amplifier circuit section (hereinafter referred to as an amplifier circuit section) that receives and amplifies and outputs a signal of the photodiode, and a second circuit that receives the output of the amplifier circuit section. A first comparison / determination circuit unit (hereinafter referred to as a first comparison / determination circuit) comprising a second operational amplifier for comparing and determining the magnitude of the reference voltage. A second comparison / determination unit having a third operational amplifier that receives the output of the amplification circuit unit and compares the magnitude with a third reference voltage and integrates and outputs the determined signal. A laser diode light emitting circuit comprising: a second comparison / determination circuit unit. The output of the first comparison / determination circuit unit and the output of the second comparison / determination circuit unit are connected, and this is used as an input to output a control signal to the base of the first NPN transistor of the drive circuit unit. 2. The laser diode light emitting circuit according to claim 1, further comprising an output limiting circuit section (hereinafter referred to as a limiting circuit section) of the NPN transistor driving circuit. 2. The laser according to claim 1, wherein the output of the first comparison / determination circuit unit and the output of the second comparison / determination circuit unit are connected and connected to the input terminal of the first operational amplifier of the drive circuit unit. Diode light emitting circuit.

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