JPH0452820Y2 - - Google Patents

Description

[Detailed explanation of the idea] [Industrial application field]

The present invention relates to a mounting device for an automatic power control circuit (hereinafter referred to as APC circuit) of an optical pickup used in compact disc players and the like.

[Summary of the idea]

By installing the driver stage of the laser diode on the main board side and mounting the part of the APC circuit that affects each circuit constant of the APC circuit that determines the LD power on the pickup side, it is possible to downsize the pickup.
It is possible to improve the efficiency of power adjustment at the production stage and to avoid variations after assembly. The above APC circuit basically consists of a control circuit 3 including a laser diode 1, a monitor diode 2, a resistor, and a fixed volume, as shown in FIG.
It is composed of a Zener diode, a comparison voltage 4 set by the base-emitter voltage of a transistor, and a transistor circuit 5 forming a driver stage for driving the laser diode 1. The applied current is converted into laser light by the laser diode 1, and its output is monitored by a monitor diode 2 (photodiode), converted into a current corresponding to the output, and used for servo. That is, the monitor current is converted into a voltage by a resistor and a semi-fixed volume in a circuit 3, and compared with a target voltage of a comparison voltage 4, and the deviation is amplified by a transistor circuit 5 to change the drive current of the laser diode. The servo will be applied to. Here, the optical output of the laser is adjusted by a semi-fixed volume in the control circuit 3, but ideally it is desirable that the same optical output can be obtained for all products. This allows you to obtain
It becomes possible to equalize the levels of RF signals.
Now, the question of where to mount the APC circuit on the product must be considered under the condition that two issues must be solved at the same time: miniaturization of the pickup and adjustment of the optical output at the production stage. No. Once the entire APC circuit (numbers 1 to 5 in Figure 1) is mounted on the pick-up body, if there is one board prepared for pick-up adjustment during the production stage, all the pick-up circuits can be mounted before assembly into the product. It is convenient because the laser output can be adjusted, but
The pick-up itself becomes large. In terms of downsizing the pickup itself, it is conceivable to mount the control circuit 3, comparison voltage power supply 4, and transistor circuit 5 shown in FIG. 1 on the main board. In this case, the adjustment of the laser power is
Adjustment at the production stage is troublesome because it must be done after assembling the pickup and the main board on which a portion of the APC circuit is mounted. In other words, if you want to make the pickup smaller, it is disadvantageous to mount the APC circuit there.On the other hand, if you want to increase the efficiency of adjustment at the production stage, it is disadvantageous to mount the APC circuit there. I want to implement it. Therefore, a method was also considered in which only the element for adjusting the laser output, that is, a semi-fixed volume, was mounted on the pickup side. Then, before assembling the product,
It is also possible to increase productivity by preparing a board for laser output adjustment, adjusting the output of all pickups, and then combining it with the main board. However, with this method, if there are variations in the values of each circuit constant of the APC circuit that determines the LD power between the adjustment board and the main board that is actually assembled in the pickup, the LD power is made equal for all products. Things become difficult.

[Problem that the invention attempts to solve]

This invention was made based on the above circumstances. For example, when using an APC circuit as shown in Figure 2,
The cause of the above variation is the comparison voltage Vref
Focusing on the constants that determine the target values of , that is, the Zener voltage V _ZD , the transistor base-emitter voltage V _B and the diode voltage V _D ,
By mounting this part, that is, up to the first stage of the APC circuit, on a pickup, replacing the board may cause the target value to change, the operating point to change, and the steady current to change, causing variations in the optical output. This is an attempt to provide a mounting structure for an auto power control circuit that eliminates the risk of damage.

[Means to solve the problem]

For this purpose, the present invention is characterized in that a driver stage for the laser diode is provided on the main board side, and a monitor current input stage including a semi-fixed volume for laser output adjustment is provided separately on the pickup main body side. That is.

【Example】

Hereinafter, one embodiment of the present invention will be described in detail with reference to FIG. Incidentally, in the figure, since the numbers 1 to 5 are the same as those in the conventional explanation, only the mounting situation thereof will be specifically described. As shown in the figure, in the circuit of Fig. 2, the elements to be mounted on the pickup side, namely the laser diode 1, monitor diode 2, control circuit 3, and comparison voltage 4, are gathered on the left side, and the laser diode 1 is mounted on the pickup side. The driving driver stage, ie the transistor circuit 5, is gathered on the right side. The left side will be mounted on the pickup side, and the right side will be mounted on the main board side. In this example, compared to the 14 parts needed to mount all of the APC circuits on the pickup side, only 7 parts are needed, which is half the number.
Contributes to downsizing of pickups. With this many parts (7 pieces), by assembling them with chip parts, there is no need to prepare a dedicated APC board.
It may also be possible to mount it on flexible substrates. Furthermore, if a main board for adjustment is prepared and placed in the production stage, since a variable volume is attached to each pickup, it is possible to adjust the laser output of all the pickups by combining it with the adjustment board. At the same time, when changing the board, the APC
Since the first stage of the circuit is mounted on a pickup, the target value does not change, the operating point remains constant, the steady state current is stable, and variations in optical output are avoided.

[Effect of the idea]

The present invention, as detailed above, can contribute to the miniaturization of pickups, and at the production stage,
Laser output can be adjusted for all pickups before they are combined with the main board, and variations in output can be minimized, and power adjustment after assembly is unnecessary, improving productivity.

[Brief explanation of the drawing]

Figure 1 is a block diagram of the APC circuit according to the present invention.
FIG. 2 is a circuit diagram showing an example of an actual circuit configuration, and FIG. 3 is a circuit diagram showing a mount structure according to an embodiment of the present invention. 1... Laser diode, 2... Monitor diode, 3... Control circuit, 4... Comparison voltage, 5...
transistor circuit.

Claims (1)

[Scope of utility model registration request] A mount for an auto power control circuit characterized in that a driver stage for the laser diode is provided on the main board side, and a monitor current input stage including a semi-fixed volume for laser output adjustment is provided separately on the pickup main body side. Device.