JPH01259585A - Automatic output control circuit for semiconductor laser - Google Patents

Abstract

PURPOSE:To enable a semiconductor laser to be driven with a low dissipation by providing a control circuit in which the semiconductor laser is driven by a current that is smoothed after a power supply current has been pulse width- modulated. CONSTITUTION:A DC voltage applied from a drive power supply 305 to a pulse width modulation circuit 302 is pulse width-modulated by the pulse width modulation circuit 302 and is supplied to drive a semiconductor laser 304 after being made to a DC having gone through a low-pass filter 303. When the optical output of the semiconductor laser 304 is decreased, the output current of a monitor photodiode 301 is decreased and the pulse width modulation circuit 302 outputs with broadened pulses to thereby increase both the DC output after the low-pass filter 303 and the optical output of the semiconductor laser. When the optical output of the semiconductor laser 304 has been increased, the DC output is decreased to thus maintain the optical output constant. The pulse width modulation circuit and the low-pass filter do not dissipate in principle. Thus, an automatic output control circuit with low dissipation can be provided.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to an automatic output control circuit for a semiconductor laser.

[Conventional technology]

Conventionally, as an automatic output control circuit for a semiconductor laser, the fourth
As shown in the figure, the optical output of the semiconductor laser 404 is detected by the monitor photodiode 401, and based on the detection result, the control circuit 402 outputs a control output to the power transistor 403, and the power transistor 403 outputs the control output to the drive power source 40.
An automatic output control circuit for controlling the current flowing from the semiconductor laser 5 to the semiconductor laser 404 is known.

[Problem to be solved by the invention]

However, the conventional automatic output control circuit
As shown in the figure, since the current is controlled by a puff transistor 403 inserted in series with a semiconductor laser 404, there is a problem in that power consumption increases.

For example, a semiconductor laser normally used in compact discs has a terminal voltage of 2V when the optical output is 3mW.
It operates with a drive current of about 70 mA, but when a power supply voltage of 12 V is used, the power consumption is 840 mW, which is six times the power consumption of 140 mW required for laser oscillation.

Therefore, in order to solve these conventional problems, the present invention aims to realize driving of a semiconductor laser with low power consumption.

[Means to solve the problem]

In order to solve the above problems, the automatic output control circuit for a semiconductor laser of the present invention includes a sensor that detects the amount of light from the semiconductor laser and outputs a signal according to the amount of light, and a sensor that detects the output of the sensor and detects the output of the sensor. An automatic output control circuit for a semiconductor laser comprising a control circuit for controlling a drive current to the semiconductor laser according to a result, the control circuit driving the semiconductor laser using a current smoothed after pulse width modulating a power supply current. It is characterized by comprising:

[For production]

FIG. 3 shows a block diagram of an automatic output control circuit for a semiconductor laser according to the present invention.

The DC voltage applied from the drive power supply 305 to the pulse width modulation circuit 302 is pulse width modulated by the pulse width modulation circuit 302, passed through a low-pass filter 303, and converted into DC voltage, which then drives the semiconductor laser 304.

Now, if the optical output of the semiconductor laser 304 decreases for some reason, the output H of the monitor photodiode 301 decreases.

Then, the output of the pulse width modulation circuit 302 is outputted with a widened pulse width, increasing the DC output after passing through the low-pass filter 303 and increasing the optical output of the semiconductor laser 304.
The light output remains constant.

Conversely, when the optical output of the semiconductor laser 304 increases, the DC output decreases and the optical output is kept constant.

Additionally, pulse width modulation circuits and low-pass filters do not consume power in principle.

In other words, an automatic output control circuit with extremely low power consumption is constructed.

〔Example〕

Embodiments of the present invention will be described below based on the drawings.

FIG. 1 shows an automatic output control circuit for a semiconductor laser according to the present invention.

Next, the circuit configuration will be explained. A triangular wave oscillation circuit (a) consisting of an operational amplifier 101, 102, a capacitor 103, and a resistor 104, 105, 106, and a monitor photodiode 1
09, an I-V conversion circuit (b) consisting of an operational amplifier 107 and a resistor 108, and resistors 110, 111.
A pulse width modulation circuit (C) consisting of 112, 113, an operational amplifier 114, 115, a diode 116, 119, and a transistor 117, 118, and a low pass filter (d) consisting of a choke coil 120 and a capacitor 121.
It consists of two blocks.

Next, the operation of the circuit will be explained. The output of the triangular wave oscillation circuit (a), the output of the I-V conversion circuit (b), and the optical output setting terminal 12
After the operational amplifier 114 adds the set value to diode 1, the operational amplifier 115 performs a comparison operation, and the diode 1
After output amplification by 16.119 and transistors 117.118, choke coil 120 and capacitor 121
The semiconductor laser 122 is driven through a low-pass filter (d) consisting of the following.

Next, the operating state will be explained using FIG. 2. Figure 2(a)
is the output waveform of the operational amplifier 114.

When the set value applied to the optical output setting terminal 123 and the optical output of the semiconductor laser 122 are equal, the output waveform of the operational amplifier 114 becomes as shown in 201, and the output waveform of the operational amplifier 115 becomes as shown in FIG. 2(b).

Here, if the optical output of the semiconductor laser 122 is reduced for some reason, the photocurrent of the monitor photodiode 109 is reduced, so the output waveform of the operational amplifier 114 is
2, and the output of the operational amplifier 115 is as shown in Fig. 2 (c
), and the pulse width is wider than that in FIG. 2(b), so the DC output after passing through the low-pass filter in FIG. 1(d) increases, and the optical output of the semiconductor laser 122 increases.

Conversely, when the optical output of the semiconductor laser 122 increases for some reason, the optical output is decreased by the opposite mechanism.

By performing pulse width modulation in this manner, optical output can be stabilized.

〔Effect of the invention〕

The automatic output control circuit for a semiconductor laser according to the present invention has the following advantages.

(i) By driving the semiconductor laser extremely efficiently, power consumption is reduced, and battery life can be increased by more than five times when powered by batteries, greatly improving battery life when applied to portable compact discs, etc. .

(ii) Since the power consumption of the control circuit is reduced, there is no need for heat radiation and the control circuit can be miniaturized.

(iii) Since the semiconductor laser is driven through a low-pass filter, it has strong surge resistance and is suitable for eA such as slow starters.
No protection circuit is required.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of an automatic output control circuit for explaining an embodiment according to the present invention. FIGS. 2(a), 2(b), and 2(C) are graphs of output waveforms for explaining an embodiment of the present invention. FIG. 3 is a block diagram for explaining the present invention in detail. FIG. 4 is a block diagram for explaining a conventional automatic output control circuit. 101.102.107.114.115...Operational amplifier 103.121...Capacitor 104.105.106.107.108.110.1
11.112...Resistor 109...Monitor photodiode 116.119...Diode 120...Choke coil 122...Semiconductor laser 123...Optical output setting terminals 201, 202...Output waveform 301 ... Monitor photodiode 302 ... Pulse width modulation circuit 303 ... Low pass filter 304 ... Semiconductor laser 305 ... Drive power supply 401 ... Monitor photodiode 402 ... Control circuit 403 ... Power Transistor 404... Semiconductor laser 405... Driving power supply and above Applicant Seiko Epson Co., Ltd. Agent Patent attorney Masayoshi Kamiyanagi (Ike 1) Ko 2) A

Claims (1)

[Claims] A semiconductor laser comprising a sensor that detects the amount of light from a semiconductor laser and outputs a signal according to the amount of light, and a control circuit that detects the output of the sensor and controls a drive current to the semiconductor laser based on the detection result. An automatic output control circuit for a semiconductor laser, characterized in that the automatic output control circuit for a semiconductor laser is provided with a control circuit that drives the semiconductor laser using a current that is smoothed after pulse width modulating a power supply current.