Such a basic circuit can only drive the motor in one direction. A
circuit (Figure 7.12) involving four transistors, in what is termed an
H-circuit, can be used to control both the direction of rotation of the
motor and its speed. The motor direction is controlled by which input
receives the PWM voltage. In the forward speed motor mode, transistors
1 and 4 are on and current flow is then from left-to-right through the