JPH02119193A - Laser driver circuit - Google Patents

Abstract

PURPOSE:To avoid destruction of information by a method wherein a laser light source can be operated only when a supply source is normal. CONSTITUTION:If one or both of source voltages +V and -V is abnormal, an electric source level detector 23 outputs an L-level detection signal 23a or 23b even if an H-level light emission instruction signal 5a is outputted by a CPU 5. A switching signal generator 25, therefore, outputs an L-level light emission instruction signal 25a. In accordance with the instruction signal 25a, a switching circuit 3 prohibits an electric source supply to a semiconductor laser 7. If the source voltage is not normal, therefore, the operation of the semiconductor laser 7 can be discontinued securely. This constitution prevents the damage to a light emission source and the destruction of optical information.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a laser drive circuit that supplies driving power to a laser emission source to drive a laser.

(Prior Art) Laser light is used as a light source for optical information processing because it is more monochromatic than other lights, has a uniform phase, and has good straightness. In particular, semiconductor lasers using semiconductors are highly reliable, and output light can be modulated quickly and directly by flowing current, so they are used for reading information stored in optical information storage media such as optical disks.

As a conventional laser drive circuit for driving such a semiconductor laser, the one shown in FIG. 3 is known. The laser power source 101 outputs a predetermined voltage 1,=indenter V to the switching circuit 103.

As shown in FIG. 4, the switching circuit 103 includes a Zener diode ZD1, resistors R1, R2, R3, and R4.
It is composed of transistors TR1 and TR2, and C
When the H level light emission command signal 105a is input from the PU 105, the transistors TR1 and TR2 are turned on and the power supply voltage V from the laser power supply 101 is applied to the semiconductor laser 10.
Supply to 7.

The monitor diode 109 is built into the same package as the semiconductor laser 107, receives part of the light emitted by the semiconductor laser 107, and outputs a signal corresponding to the received light m, that is, a monitor signal, to the monitor light detection circuit 111. do.

The monitor light detection circuit 111 and the light output error generation circuit 113 constitute an APC (AUTOPOWERC0NTR0L) circuit, which compares the value of the monitor signal with a preset reference value and outputs the error signal. Adjustment is made so that the optical output from the laser 107 is constant. The switch 115 operates under control from the CPU 105, for example, in synchronization with the light emission command signal 105a. The semiconductor laser drive circuit 117 is connected to A via the switch 115.
When an error signal from the PC circuit is input, the optical output of the semiconductor laser 107 is corrected in accordance with this error signal.

(Problems to be Solved by the Invention) However, in the conventional semiconductor laser drive circuit, the CPU1
The switching circuit 103 is controlled only by the light emission command signal 105a from the CPU 105, and if noise or the like is mixed into the power supply voltage, for example, the CPU 105 may perform erroneous control. Also, the semiconductor laser 1
If the power supply is suddenly interrupted while the 07 is being driven, or if the power supply voltage fluctuates, various circuit sections will malfunction. As a result, if a large current flows to the semiconductor laser 107, there is a risk that the semiconductor laser 107 will be damaged or the optical information recorded on the optical disc or the like will be destroyed due to the large optical output from the semiconductor laser 107.

The present invention has been made in view of the above problems, and even if an abnormality occurs in the supplied power, it will not damage the semiconductor laser or damage the optical information recorded on an optical storage medium such as a laser disk. The aim is to reliably prevent damage and provide a highly reliable laser drive circuit.

[Structure of the Invention] (Means for Solving the Problems) In order to achieve the above object, a laser drive circuit provided by the present invention includes a power supply means for supplying power for driving a laser light source in accordance with an input light emission command; determining means for determining whether or not the power supplied from the power supply means is normal; and outputting a light emission command to the power supply means when the determination means determines that the power supply is normal. and a light emission command control means.

(Function) The present invention has a determining means for determining whether or not the power supplied from the power supply means is normal, and when the determining means determines that the power is normal. The light emission command control means outputs the light emission command to the power supply means. Therefore, the power supply means inputs the light emission command only when the power supply is normal, and drives the laser light emitting source based on this light emission command. In addition, if the power supply is abnormal, the emission command will not be input to the power supply means, resulting in damage to the laser emission source or destruction of information on the optical recording medium when the power supply is abnormal. can be reliably prevented.

(Embodiment) An embodiment of the present invention will be described in detail below with reference to the drawings.

First, the configuration will be explained with reference to FIG.

A laser power source 1 is connected to a switching circuit 3 and outputs a predetermined core EA voltage of 10 V to the switching circuit 3. The switching circuit 3 is connected to the switching signal generation circuit 21, and is also connected to the semiconductor laser 7 and the monitor diode 9, respectively. switching circuit 3
is the light emission command signal 2 from the switching signal generation circuit 21
5a, a switching operation is performed based on this light emission command signal 25a, and a predetermined power supply voltage +V from the laser power supply 1 is supplied to the conductive laser 7 and the monitor diode 9. As described later, the light emission command signal 258+ is a signal created based on the light emission command signal 5a from the CPU 5, which is the section 4, and the switching circuit 3 is activated when the light emission command from the control section is input. This is a power supply means for supplying power to the semiconductor laser 7, which is a laser emission source.

Next, the internal structure of the switching circuit 3 and its connection structure with peripheral devices will be explained in detail with reference to FIG.

The emitter of the transistor TR2 is connected to the laser power source 1, and the power source voltage +V is applied from the laser core source 1. A resistor R4 is connected between the emitter and base of the transistor TR2, and the collector of the transistor TR2 is connected to the semiconductor laser 7. Also, transistor TR2
The base of is connected to the collector of the transistor TR1 via a resistor R3. ]・The base of the Raran jitter TR is connected to the ground via resistors R2 and R1, and the base of the resistor R
The connection point between 1 and R2 is connected to the output terminal of an AND circuit forming the switching signal generating circuit 25 via a Zener diode ZD1. Therefore, transistors TR1 and TR2 are turned on in response to the light emission command signal 25a, which is an AND output from the switching signal generation circuit 25, and supply the power supply voltage + to the semiconductor laser 7.

Referring again to FIG. 1, the semiconductor laser 7 and the monitor diode 9 are enclosed in a single package in a facing state, and the emitted light from the semiconductor laser 7 is output to the outside of the package, and the emitted light is A part of the signal is supplied to the monitor diode 9. The monitor diode 9 is connected to the monitor light detection circuit 11, and when it receives part of the light emitted by the semiconductor diode 7, it outputs a current corresponding to the received light ω to the monitor light detection circuit 11 as a monitor signal. When the monitor light detection circuit 11 receives a monitor signal from the monitor diode 9, it converts it into a voltage signal and outputs it.

The optical output error generation circuit 13 is connected to the monitor light detection circuit 11, and inputs the monitor signal converted into the voltage signal described above. Further, the optical output error generation circuit 13 has a built-in comparator and the like, and compares the voltage value of the monitor signal inputted from the monitor light detection circuit 11 with a preset reference voltage value, and outputs the resulting error signal. The semiconductor laser drive circuit 17 is connected to the optical output error generation circuit 13 via the switch 15 and is also connected to the semiconductor laser 7 .

The switch 15 operates under control from the CPU 5, for example, in synchronization with the light emission command signal 5a. Specifically, the optical output error generation circuit 13 and the semiconductor laser drive circuit 17 are connected at the timing when the H level light emission command signal 5a is output. When the semiconductor laser drive circuit 17 receives the error signal from the optical output error generation circuit 13 via the switch 15, it corrects the optical output of the semiconductor laser 7 in accordance with this error signal. This adjusts the optical output from the semiconductor laser 7 to be constant.

Also, the monitor light detection circuit 11. Optical output error generation circuit 13.
Each of the semiconductor laser drive circuits 17 operates in response to supply of power supply voltage V and ~2 from a power supply circuit (not shown).

Next, the internal configuration of the switching signal generation circuit 21 and its connection configuration with peripheral devices will be explained with reference to FIG.

The switching signal generation circuit 21 is the power level detection circuit 2
3 and a switching signal generating circuit 25. The power level detection circuit 23 includes a detection circuit 23A for detecting an abnormality in the power supply voltage +V, a detection circuit 23B for detecting an abnormality in the power supply voltage -2, a resistor R14, and an inverter 29.

The input terminal P1 of the detection circuit 23A is connected to a power supply circuit (not shown), and is also connected to the collector of the transistor TR11 via a resistor R12. Also, input terminal P
A Zener diode ZD11 and a resistor R11 are connected in series between 1 and ground.
The connection point between D11 and resistor R11 is connected to the base of transistor TR11 via resistor R13. As soon as the emitter of the transistor TR11 is connected to the ground via the resistor R14, the switching
It is connected to the input terminal of 5. Therefore, when a predetermined power supply voltage +V is input to the input terminal P1, the transistor TR1
1 is turned on and outputs an H level detection signal to the input terminal of the switching signal generation circuit 25. Further, when the value of the power supply voltage 10 V input to the input terminal P1 decreases to a predetermined value or less, the transistor TR11 is turned off and outputs an L level detection signal to the input terminal of the switching signal generation circuit 25.

An input terminal P2 of the detection circuit 23B is connected to a power supply circuit (not shown) and receives a power supply voltage +V. Also, the detection circuit 23B
The input terminal P3 is connected to a power supply circuit (not shown) and receives a power supply voltage -■. Input terminal P2 is resistor R17, R18
and is connected to an input terminal of the switching signal generation circuit 25 via an inverter 29. Resistors R17 and R18
The connection point with the input terminal P3 is connected to the input terminal P3 via the Zener diode ZD12. Further, a connection point between the resistor R18 and the two inverters is connected to ground via a diode D11.

Therefore, input terminal P2. Power supply voltage input to P3 +V, -
When the value of V is a normal value, an L level detection signal is applied to the inverter 29, and an H level detection signal inverted by the inverter 29 is output to the input terminal of the switching signal generation circuit 25. Also, input terminal P3
When the value of the power supply voltage -■ input to changes to the positive side, L
The level detection signal is output to the input terminal of the switching signal generation circuit 25.

The switching signal generation circuit 25 outputs the AND output of the light emission command signal 5a from the CPU 5, the detection signal from the detection circuit 23A, and the detection signal from the detection circuit 23B to the switching circuit 3 as a light emission command signal 25a.

Next, the operation will be explained.

First, the operation when the power supply voltages +V and -V are both normal values will be explained. When the power supply voltage terminals V and -V are both normal values, the power supply level detection circuit 23 detects that the power supply voltage +V is normal and outputs an H level detection signal 23a, and also detects that the power supply voltage +V is normal. detects that it is normal and outputs an H level detection signal 23b. When the CPU 5 outputs the light emission command signal 5a at the H level in this state, the switching signal generation circuit 25 outputs the light emission command signal 25a at the H level to the switching circuit 3. As a result, the power supply voltage V from the laser power supply 1 is applied to the semiconductor laser 7, and the monitor diode 9. Monitor light detection circuit 11. Optical output error generation circuit 13. Each of the semiconductor laser drive circuits 17 operates to adjust the optical output from the semiconductor laser 7 to a constant value.

Next, the operation will be described when either the power supply voltage +V or -■ is abnormal, or when both the power supply voltages V and -V are abnormal. Even if the CPU 5 outputs the light emission command signal 5a at the H level during such a power abnormality, the power level detection circuit 23 outputs the L level detection signal j% 23a or 23b. is L level light emission command signal 2
5a is output. As a result, the switching circuit 3 prohibits the supply of power to the semiconductor laser 7. Therefore, if the power supply voltage is not normal, the operation of the semiconductor laser 7 is reliably stopped.

In the embodiment shown in FIG. 2, the power level detection circuit 23
has tried to detect whether the values of both the power supply voltage terminals V and -V are normal or not, but it is necessary to detect whether the value of either power supply voltage is normal or not. With this configuration, the circuit configuration can be simplified.

[Effects of the Invention J As explained above, according to the present invention, the laser emission source can be operated only when the supplied power is normal, so the laser emission does not occur when the power supply is abnormal. By reliably stopping the operation of the laser source, damage to the laser source and destruction of recorded optical information can be prevented.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a circuit diagram showing the main parts of FIG. 1, FIG. 3 is a block diagram showing a conventional example, and FIG. FIG. 2 is a circuit diagram showing the switching circuit shown in the figure and its peripheral devices. 1...Laser power supply 3...Switching circuit 5...CPU 7...Semiconductor laser 23...Power level detection circuit 25...Switching signal generation circuit

Claims (1)

[Scope of Claims] A power supply means for supplying power for driving a laser light emitting source according to an input light emission command; a determining means for determining whether or not the power supplied from the power supply means is normal; A laser drive circuit comprising: a light emission command control means for outputting a light emission command to the power supply means when the determination means determines that the power supply is normal.