tinska.h
Junior Member level 2
Greetings,
I'm building an obscuration meter which uses multiple high power IR LED to illuminate sample, then a photodiode is used to measure transmittance. Since external IR-sources and noise are distorting results significantly, I've utilized phase sensitive detection to minimize errors. However due to this I've got to drive IR LEDs in sine(actually half sine).
Now the problem is that I can't think of any ways to drive these IR LEDs without distorting sine waveform. Also I don't have any idea how to set a maximum peak voltage level for the signal.
IR LEDs are consuming 400mA at 1.8V Vf, and I'm using 5 of them to achieve sufficient radiating power. Sine wave comes from a function generator, actually audio output from my PC and frequency is 1kHz. I'm using a diode to remove negative sine, so resulting is 0V to 1V half sine. I thought I use high current amplifier, but amps that I found usually had stable gain at over 10. Also I thought using audio amplifier, but their output current are rather small and output voltage rather high. MOSFETs and BJTs I've played with usually distorts the signal.
Another problem with audio output as function generator is that I've experienced some fluctuations with input signal in terms of Vpk-pk. Amplitude fluctuations weights quite a lot in the final results. Maybe some automatic gain control or voltage controlled resistor? Zener diodes would just clip the signal if it exceeds threshold.
Could anybody give me some ideas that I could investigate?
Thanks
I'm building an obscuration meter which uses multiple high power IR LED to illuminate sample, then a photodiode is used to measure transmittance. Since external IR-sources and noise are distorting results significantly, I've utilized phase sensitive detection to minimize errors. However due to this I've got to drive IR LEDs in sine(actually half sine).
Now the problem is that I can't think of any ways to drive these IR LEDs without distorting sine waveform. Also I don't have any idea how to set a maximum peak voltage level for the signal.
IR LEDs are consuming 400mA at 1.8V Vf, and I'm using 5 of them to achieve sufficient radiating power. Sine wave comes from a function generator, actually audio output from my PC and frequency is 1kHz. I'm using a diode to remove negative sine, so resulting is 0V to 1V half sine. I thought I use high current amplifier, but amps that I found usually had stable gain at over 10. Also I thought using audio amplifier, but their output current are rather small and output voltage rather high. MOSFETs and BJTs I've played with usually distorts the signal.
Another problem with audio output as function generator is that I've experienced some fluctuations with input signal in terms of Vpk-pk. Amplitude fluctuations weights quite a lot in the final results. Maybe some automatic gain control or voltage controlled resistor? Zener diodes would just clip the signal if it exceeds threshold.
Could anybody give me some ideas that I could investigate?
Thanks