Touch type electric fan speed regulating circuit

Circuit working principle: The core device of this circuit is a KH1668. Its internal
circuit is mainly composed of three parts: synchronous oscillator, frequency division counter and control logic circuit
. The internal oscillation circuit starts from the synchronization pulse. When the power is first turned on, the internal circuit
automatically resets, and pin 7 has no pulse output and is in a low level state. When pin 2 is touched for the first time
, the frequency division counting circuit counts the oscillation pulses. When the 7th pulse arrives, pin 7
jumps to high level until the synchronization pulse is close to the zero-crossing point and returns to low level, and vs is turned on.
The horns are small. When touched for the second time, when the frequency division counting circuit counts the oscillation to the fifth pulse
, pin 7 jumps to high level, and the conduction angle of vs is larger. When touched for the third time, the frequency division
counting circuit counts the first pulse of the oscillation, and pin 7 jumps to high level , and maintains it
until the synchronization pulse is close to the zero-crossing point, and the conduction angle of vs is the largest, which can reach 150. above.
When touched for the fourth time, the frequency division counting circuit stops counting and pin 7 has no pulse output, which is equivalent to
shutting down. The speed adjustment program is carried out according to the above four-level cycle action. If pin 4 of the IC is connected to
the positive terminal of the power supply, only the third and fourth triggers mentioned above will alternately complete the on/off function.