| 摘要 |
PURPOSE:To attain stable control, by switching the operation of an optical beam intensity control means with the output of a focus detecting means to make the photo detecting amount of a photo detector constant at focusing state. CONSTITUTION:When no focus is set at the application of power supply, a temperature characteristic compensating optical power control circuit 21 is operated by the light of a semiconductor laser 103, a switch 22 is selected to the position (a) to make the luminous amount incident to a photo diode 20 constant. When the focus is set at the reproducing state, a reflecting factor changing compensating optical control circuit 26 is operated by the intensity of the light of the laser 103, the switch 22 is selected to position (b) with an output of a focus OK detecting circuit 27 and the reflected light from the disc is controlled to be constant. When the focus is set at the recording state, a power control error signal 104 just before recording is held for a recording period by a sample-and hold circuit 24, the switch 23 is turned off via a recording gate signal 105 and an inverter 18 to prevent the attenuation of the sample value. Thus, stable control is attained. |
