Lamp Power Control

The Implantable Sensor with Lamp (A3030D) provides 0-100% control of the lamp power in steps of 20% by means of modulation of the lamp current, as we describe elsewhere. The 1-MHz modulation frequency is so high as to have no effect upon the activity of neurons nor our EEG amplifier. We connected an EZ500C470 470-nm blue LED to the lamp leads of an A3030D. At 100% power, the LED current is 35 mA. We varied the output power from 1-100% and measured battery current and optical output power of the LED at each step.


Figure: Optical Output Power and Battery Current versus Lamp Modulation Duty Cycle. Switching transistor is the NTR4003N. Compare to this measurement of modulation current in ISL5/6, which used the NDS355AN switching transistor.

The average ISL7 head fixture couples 44% of the LED light to the tip of its fiber. At 100% power, the LED produces 30 mW and we expect 13 mW at the fiber tip. The battery current and light intensity scale almost linearly with power setting. If anything, the 40% power setting is slightly more efficient in its conversion of battery energy into light energy than the 100% setting.