Motor Drive

The motor circuit solution is one of the key factors in improving the brushing performance of electric toothbrushes. Motor control must be performed according to the desired brushing, and the rotation speed of motor will change in real time. Motor drivers and MOSFETs are used to drive the motor. It is ideal to drive the motor without power loss for changing rotation speed. In order to control this change with the MCU, the current level flowing through the motor winding must be constantly monitored. This monitored current level is an analog signal, which is converted to a digital signal through an AD converter, which provides a signal to the MCU to accurately determine how much current is flowing in the controlled motor. Motor current is commonly monitored by a shunt resistor. The shunt resistor is connected in series with the circuit and uses Ohm's law to perform current-voltage conversion. However, when considering the overall system efficiency, the resistance must be as low as possible, resulting in low voltage. This slight voltage is fed back to the MCU for optimal control of the entire system.

A Schottky barrier diode that uses a Schottky junction of metal and n-type semiconductor has a very small V_F characteristic and does not use holes as carriers, so it can operate at high speed. By utilizing this characteristic, the counter electromotive force of the motor is short-circuited in a short time to consume energy, and the reverse voltage is not applied to the driver circuit.

Toshiba offers a lineup of low on-resistance MOSFETs to maintain stable driving in the event of sudden current fluctuations in motor drive, contributing to more efficient power utilization

The use of an ultra-low noise operational amplifier enables accurate transmission of sensed signals amplified to a higher signal level to the MCU. Combined with a shunt resistor, the optimum control of the device, fault detection, and protection circuitry of the battery can be realized.