4 channel dimmer

Remotely controlled light dimmers in theatrical and architechtural applications use 0-10V control signal for controlling the lamp brightness. In this case 0V means that the lamp is on and 10V signal means that the lamp in fully on. A voltage between those values adjust the average voltage which is applied to the ligh bulb. This average voltage controlling is made by
4 channel dimmer - schematic

controlling the position in which phese the output triac fires (sooner it fires more power is applied to lamp). The the phase when the TRIAC will fire is controlled by the input voltage which is compared to an internal ramp signal generated by the dimmer. In this arrangement the input voltage linearly controls the time delay between mains zero crossing and the triac triggering. This circuit is a real core of the dimmer system. This circuit generates ramp 100 Hz signal which is syncronized to the incoming mains voltage. The ramp signal which is generated will start form 10V and go linearly down to 0V in 10 milliseconds. At the next mains voltage zero crossing the ramp signal will again immediatly start from 10V and go down to 0V. This same ramp signal is fed to all of the 4 comparators in the dimmer. The following ramp signal generator is quite simple ramp generator based on discrete transistors which do some switching, capacitor and a constant current source made by using one transistor. The idea of the circuit is taken from N-channel light dimmer design made by Kari Hautio. Trimmer R5 is used in controlling the ramp signal. If you have an oscilloscope, then it is best to use it to look at the situation so that the signal send by the circuit is what is described eariler. A good approximation is so start at position that R5 is set to it`s center position. Besides generating the ramp signal the sampl generator circuit works...

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