Advanced Light Dimmer

  
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.
Advanced Light Dimmer - schematic

Besides generating the ramp signal the sampl generator circuit works as a power supply comaprator part of the dimmer. The 13.5V unstabilized output is used to power the comparator section (that putput can be loaded up to 100 mA). The 10V stabilized voltage is used only for internal use in ramp generator (that stabilized 10V voltage can be also used for some extra low power circuitry which need 10V voltage, for example local dimmer controls if such thign are needed). The circuit works so that the comparator output in low when the input voltage is higher than the ramp voltage. When the ramp signal voltage gets lower than the input voltage the comparator output goes high which causes that current starts to flow through resistor to optocoupler which causes the triac to cnoduct. Because the ramp signal starts at every zero crossing from 10V and goes linearly to 0V at the time of one half cycle the input voltage controls the time when the triac is triggered after every zero crossing. This effectively means that the control voltage controls the ignition phase of the triac. The output of the comparator is a pulse width modulated signal is is syncronized to mains voltage. The start of every PWM pulse changes the position depending on control voltage and the end is at zero crossing of mains votlage. The start of the pulse is used to trugger the output triac. The triac card contains four controlling circuits similar to circuit...



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