Linear Amplifier Motor Driver
A simple driver for a motor is a "push-pull" current amplifier. This circuit uses two transistors to "push" or "pull" current through the motor. The transistors are npn-type and are activated by an applied voltage. The op-amp linearizes the circuit and provides a current gain. The input is an analog voltage.
One of the problems with this circuit is that it isn't very efficient. Lots of power is dumped into ground and into heat. Large heatsinks are required for the transistors even when using small motors. For a more efficient method, consult Pulse Width Modulation.