This is a simple TRIAC AC load dimmer used to
control the power of a resistive load such as
incandescent lamp or heater element. The max load it
can handle is 400VA. Such a circuit is often found
on cheap commercial light dimmers and is proven to
work reliable for the rated power.
The circuit is working
by controlling the phase of the 220VAC voltage
allowing the load to be powered for less than 360º
of the full sine wave. Powering the load for smaller
period than full sine wave delivers less power, so
it has a dimming effect on the load.
Control is done throught R2 potentiometer
which controls the time needed for the C2 to be
charged through R1-R2. C2 is charging until it
reaches the breakdown voltage of DIAC D1 which then
fires the TRIAC T1. Once the TRIAC is contacting the
circuit is closed and the load receives power.
The rate which C2 charges determinates the point
on 220VAC sinewave where it reaches the breadown
voltage of DIAC. So, slow C2 charging means that the
DIAC conducts at the end of AC period and fast C2
charging means that DIAC conducts at the beggining
of AC sine.
Components L1 and C1 act as interference suppression
filter reducing RF emmitions.
Circuit is directly
connected to mains voltage, so lethal voltages
present all over the board. Take care!
should have a plastic spindle to provide sufficient
3D PCB renderings
||3.9K - 1/4W
||33nF / 400V
||19 turns of
0.8mm enamel wire on 4mm ferrite core
files in Eagle format