Small electric transportation vehicles such as mobility scooters for the elderly, industrial warehouse utility carts, electric wheelchairs, electric "go-peds", and electric boats represent a growing market for low-cost, brush driven motors. For applications at one horsepower and below, such as mobility scooters and wheelchairs, brush commutated permanent magnet DC motors are typically used. In applications above two horsepower, a series wound field motor is often used. These applications require motors operating at voltages well below 50 volts due to safety issues, and thus very high currents are involved. The power MOSFET gate driving and biasing for the requisite motor control conventionally comprised an entire circuit board filled with discrete logic, op amps, comparators and oscillators to create the PWM, charge pump, and drive circuitry that can now be obtained from a small, inexpensive 8-pin microcontroller combined with a high peak-current, gate driver IC. This paper will describe a scalable reference design that has been developed to drive dc brush commutator motors ranging in power from 1/4 hp to 1.5 hp at battery voltages from 9V to 24V.
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