Patent ID: 8907607

Claim:
A soft start circuit for a forward/reverse rotation fan includes: a forward/reverse switch unit enables to receive a high level signal or a low level signal; a soft start activation unit having a first signal transmission loop and a second signal transmission loop, when the soft start activation unit receives the high level signal, the first signal transmission loop outputs a first instantaneous signal; when the soft start activation unit receives the low level signal, the second signal transmission loop outputs a second instantaneous signal; a soft start control unit, when the soft start control unit receives the first instantaneous signal or the second instantaneous signal, the soft start control unit outputs a control signal; a Hall IC; and a driver IC having a speed control terminal, when the forward/reverse switch unit receives the high level signal, the Hall IC drives the driver IC via the forward/reverse switch unit to make the fan rotate in a second direction; when the forward/reverse switch unit receives the low level signal, the Hall IC drives the driver IC via the forward/reverse switch unit to make the fan rotate in a first direction, wherein the first instantaneous signal or the second instantaneous signal of the soft start circuit activates the soft start control unit to make the control signal varied from low level to high level, when the rotation direction of the fan is switched from the first direction to the second direction or switched from the second direction to the first direction, the fan enables to start rotation in a soft start mode owing to high level of the control signal transmitted from the soft start control unit to the speed control terminal during initial rotation of the fan.