Hi everybody
I am an unexperienced hobbyist in electronics. Recently I have build a sunrise lamp, based on triac switching. The PWM scwitching has been accomplished by a linear 30 min voltage ramp and a 100 Hz sawtooth voltage, which are combined to a variable duty cycle rectangular voltage by a comparator. The system works fine, but the increase in brightnes is not linear with the voltage ramp: at first the brighthess increases slowly, it is most rapidly increased at about 15 minutes, and the brightening slows again at the end of the (linear) voltage ramp.
I am not sure, but I think the reason for this unlinear increase is the sine waveform of AC, which seems to cause the increase in voltage to follow an "S-shape" allthough the increase of the duty cycle of the triggering singnal is linear.
How to solve this unlinearity? Is it possible to construct an "inverted S" voltage ramp to compensate the unlinearity. Bellow is a crude modell as a character graphics.
Voltage x
I x
I x
I x
I x
I x x x
I x
I x
I x
I x
I x
__________________________________> Time
Mikko
I am an unexperienced hobbyist in electronics. Recently I have build a sunrise lamp, based on triac switching. The PWM scwitching has been accomplished by a linear 30 min voltage ramp and a 100 Hz sawtooth voltage, which are combined to a variable duty cycle rectangular voltage by a comparator. The system works fine, but the increase in brightnes is not linear with the voltage ramp: at first the brighthess increases slowly, it is most rapidly increased at about 15 minutes, and the brightening slows again at the end of the (linear) voltage ramp.
I am not sure, but I think the reason for this unlinear increase is the sine waveform of AC, which seems to cause the increase in voltage to follow an "S-shape" allthough the increase of the duty cycle of the triggering singnal is linear.
How to solve this unlinearity? Is it possible to construct an "inverted S" voltage ramp to compensate the unlinearity. Bellow is a crude modell as a character graphics.
Voltage x
I x
I x
I x
I x
I x x x
I x
I x
I x
I x
I x
__________________________________> Time
Mikko