As a light source of the optic sensor

the stability of output power of the semiconduct laser has a direct effect on the accuracy of the sensor.A driving circuit is designed according to the working principle and output characteristic of the light source for fiber-optic sensor applied in the low temperature.The driving circuit based on the automatic power controller（APC） is fabricated by slow-start circuit avoiding noise from power supply and prolonging the using time of the laser.The testing results show that the output power is very stable and the stability is superior to 0.5 %.