Dimming light circuit with gradual brightening and dimming function

It is a novel
thyristor dimming light circuit. It
can not only dim the light, but
also change the light from dark to bright every time the light is turned on
; when the light is turned off, the light
gradually changes from bright to dark.
    220V AC mains power (that is,
alternating current, loosely called) is stepped down by G
, rectified by VD1 and VD2, vs. regulated and C. After filtering, the 12V stable DC voltage is output for use by the control circuit
. The single-junction transistor vu forms an oscillator to excite the bidirectional thyristor VTH. Its oscillation frequency is determined by the
collector current of VT2. The current is controlled by the potentiometer RP2 on the one hand and the collector
potential of VT1 on the other hand.
    When switch S is closed, G passes through R. Start charging, C. As the voltage at both ends gradually increases, VTI
gradually changes from the original cut-off state to the amplified state, and its collector potential gradually decreases, so that the base current of VT2 gradually
increases, and the charging current of the capacitor G also gradually increases. As a result, the oscillation frequency of vU gradually increases from low to high
, and the lamp E changes from dark to bright. When the voltage across the island rises to the point where VT1 is saturated and turned on, the collector current of VT2
is no longer controlled by VT1, but is only controlled by potentiometer RP2
. At this time, adjusting RP2 can continuously dim the lamp F. This is the process of gradually turning on the light.
    When switch s is turned off, Cz passes through R. When the emitter junction of VT1 discharges, its terminal voltage gradually decreases, and VT1
transitions from the original saturated state to the amplified state. At this time, the collector current of VT2 is controlled by VT1 and decreases
, causing the vu oscillation frequency to gradually decrease, thus causing the light to gradually dim from the originally set brightness. When VT1
is completely cut off, VT2 is also cut off because there is no base bias, which causes vu to stop oscillating, thyristor VT4 is turned off, and the lamp E
goes out. This is the fade-out process when the lights are turned off.
    The trimming resistor RP1 is used to adjust the gradual transition time of the light from dark to bright and from bright to dark. Using
the data shown in the figure, the transition time can be adjusted within 3-5s. G and R. It is an overvoltage protection network for thyristor VTH
and can also absorb high-frequency interference pulses.