Time base circuit AC dimmer circuit

It is a NE5 55 time base circuit that can achieve zero-crossing triggering of the AC multi-channel fluorescent lamp. The NE5 55
time base circuit is connected into a non-
steady-state self-excited polynomial oscillator .
When switch S is opened, capacitor
C cannot be charged, pins ② and ⑥
are low power, r, the oscillator
stops, the time base circuit is in the set
state, pin ③ outputs high level , and
VD3 is cut off. At this time, the positive power supply
passes through R. ,R. When the voltage is divided, the three-switch
tube VT1 is turned on, so the thyristor
VTH can get the trigger current
to turn on, and the lamp E is fully lit. After closing the switch, the oscillator composed of NE555 starts to vibrate, and pin ③ outputs
high/low level alternately. When pin ③ outputs high level, the thyristor WrH is turned on; when pin ③ outputs low level
. VD3 is turned on-wri is cut off because the base is clamped at a low level, the thyristor VTH loses the trigger current, and
turns off when the alternating current crosses zero. Therefore, the average value of the current flowing through the bulb E becomes smaller and the brightness becomes darker. In an
oscillation cycle, the output low level time of pin O/ is fixed, which is determined by the discharge time constant of R:, t,
while the time of outputting Imu level is determined by (R-+ Rl'), C. Determined by the charging time constant. Therefore, depending on the size of the segment RP
, the brightness of the bulb E can be continuously and steplessly changed.