Thyristor dimming lamp circuit with light stabilization function (1)

The thyristor dimming lamp circuit with light stabilizing function is shown on the website 44. It is based on the ordinary bidirectional thyristor dimmer
and adds a light digging circuit, so that it has the function of automatically tracking the brightness of the surrounding environment.
    S2 in the figure is an automatic light stabilizing switch. When sz
is turned on, it is a neon bulb triggered bidirectional
thyristor dimmer. Its working principle is shown in Example
32 of this chapter, and will not be repeated here. At this time,
the potentiometer RP1 can be adjusted to adjust the brightness of the bulb E as desired
. When automatic light stabilization is required,
the switch S2 can be closed. At this time, the resistance (Chi. + RP2 +
RI.) is connected in parallel with the capacitor C, which together with (R, +
RPl) determines the charging rate of the capacitor C.
On the one hand, the charging rate of C is determined by the (R. leaf RP1)
branch, so adjusting the resistance of RP1 can still reduce the brightness of the lamp E; the charging rate of C is affected by the (R. + RP2 +
RI.) branch, where RI. It is a photoresistor, and its resistance
changes due to changes in ambient illumination. When the ambient illumination is high, RL has low resistance, so the charging rate of C slows down, the conduction angle of the gate tube VTH
becomes smaller, and the luminous brightness of the lamp E decreases; if the ambient illumination gradually decreases, the shunt function of the vertical circuit decreases
, so the charging rate of c is accelerated, the VTH conduction angle gradually increases, and the brightness of the lamp E also increases, thereby
achieving the purpose of stabilizing the illumination of the illuminated work surface.
    Car circuits are very suitable for making vision protection desk lamps, because reading and writing require appropriate and stable illumination. When
S2 is unlocked, it is an ordinary dimming desk lamp. When S2 is closed, it is an automatic light-stabilizing desk lamp. After the S2 is idle,
the RP1 can still be used to adjust the brightness. Once the illumination is set, the brightness of the desk lamp can automatically track changes in ambient light intensity
to ensure that the illumination of the reading and writing surface remains unchanged, thus achieving vision protection. On the installation day, attention should be paid to
placing the light-transmitting 7L of RL on the side of the desk lamp base so that it can feel the changes in light intensity of the surrounding environment but
cannot be illuminated by the light of the desk lamp E itself. The function of the trimming resistor RP2 is to adjust the sensitivity of the automatic light stabilization
. After the circuit is installed, use a small screwdriver to carefully adjust the RP? to ensure that the automatic light stabilization function can function normally.