DETECTOR OF CROSSING FOR ZERO:
To be able to detect the crossing for zero of the sign of the line of 120Vac to 60Hz there isdesigned a simple circuit based on a transformer that reduces the sign of 120VAC to 12VAC. The sign is rectified using a bridge of diodes and it removes to an operational amplifier working likecomparator. The wave is compared with a value understood between 0 and 1V that is generated by the dimmer RV14 GIVES 100K?. This way when the sign of 12VAC is minor that the voltage provided from the dimmer,the operational amplifier will produce a pulse and his extent will be equal to the time in which the crossing lasts for zero.
GENERATOR OF RAMP:
The sign of ramp is generated by the linear load ofthe capacitor C2 of 1uF. This is obtained stabilizing, with a Zener diode, the voltage and consequently the current of the base of the transistor Q2 (2N3906). This way the issuer's current remainsalso stabilized and the capacitor meets obliged to be loaded on the same speed always, that adjusts with the dimmer RV2 placed in the issuer of this transistor. With the pulse of the crossing forresultant zero of the comparison of the wave without stabilizing with a value near zero, we manage to do the cut to the load in the wished point doing that the capacitor disburdens immediately generatingthis way the sign of ramp.
VOLTAGE OF REFERENCE OR SET POINT:
This circuit allows us to fix the point of work of the load of controlling Delivering a voltage of component DC that is obtained from asource of 15 V and a divisor of simple voltage between the resistance R5 and the dimmer RV3, the diode located between the third terminus of the dimmer and the connection to land us takes chargeproviding a voltage of 0.6 volts when the dimmer is in his maximum range and thus to support the circuit in functioning. This voltage of reference we send it to the stage comparadora of the system.