| 摘要 |
PURPOSE:To simplify circuit constitution, by a method wherein an optical isolator is directly driven by a specified DC power source out of a plurality of DC power sources whose voltages are different and whose polarity is not uniform, the other DC power sources are switched in thereby, and a sequence between a plurality of the DC power sources is given. CONSTITUTION:The semiconductor laser driving circuit 2, etc. of a laser printer applying a semiconductor laser 1 are supplied with voltages from electric power sources 3-5. Until all the output voltages of the power sources rise up higher than threshold levels V1-V3, optical switches 10 and 12 are not in the state of ON, and the output level of an inverter 13 is low. Accordingly, the state of an AND-gate 15 is OFF and keeps the semiconductor laser driving circuit 2 in the disable state. When all the output voltages of the power sources 3-5 rise up higher than the respective threshold levels V1-V3. the optical switches 30 and 12 turn ON, and the output level of the inverter 13 becomes high. Thus the AND-gate 15 is opened and the enable state is kept. |
