Abstract: The application provides a gear control circuit and system for an alternating current motor. The gear control circuit includes: a plurality of controllable switches; a detection unit, configured to detect switching statuses corresponding to the controllable switches; a gear input unit, configured to receive a target gear m inputted from outside; and a control unit, connected to the gear input unit and configured to obtain the target gear m. The application also provides a switch controller and an electronic device. The switch controller includes a signal modulation circuit, a signal follower circuit, a comparison circuit, and a switch control circuit. The switch controller may perform digital-to-analog conversion by using the signal modulation circuit, to modulate a first PWM signal being a digital signal into a second PWM signal being an analog signal, and then the signal follower circuit performs load amplification on the modulated second PWM signal.

Abstract: The application provides a driving circuit. The circuit includes: a segment display, including a plurality of light-emitting units; a controller, configured to generate a control instruction for the segment display according to a configuration signal; a digital driver, connected to the controller, and configured to generate a pulse driving signal according to the control instruction from the controller; and an amplification circuit, with one end being connected to the digital driver and the other end being connected to the plurality of light-emitting units of the segment display. The application also provides a magnetic sensing circuit and an electrical device. The magnetic sensing circuit includes a magnetic sensor, a sensing selection circuit, and a result representation circuit. A plurality of magnetic sensors are provided, and at least some of the plurality of magnetic sensors are capable of being connected to the sensing selection circuit by a sensing output terminal.