DC motors convert electrical energy into mechanical energy. Isolated applications that have historically been mechanical in nature can now be added to control architectures to drive system costs down and provide the control fidelity, protections, and diagnostics necessary to ensure efficient use and system safety. There are several attributes of DC motors that need to be understood to help define the best control strategy for a particular application. The torque or mechanical energy available for any motor application is directly proportional to the current through the motor. The current in the motor will be limited at a given voltage to the effects of the resistive, inductive, and electromotive characteristics of the motor windings and permanent magnets. The third relationship is the relationship of the back electromotive force (BEMF) to the speed of the turning motor. The resistance is associated with the wire and the windings in the motor and is the main factor defining maximum current that a motor will draw when it is in a stalled state and no inductive or electromotive effect is in place. The voltage dropped across the inductance of the motor is also associated with the metal windings and increases or decreases with the rate of change associated with the current in the motor. The inductance can be used to the designer’s advantage by providing a constant or smooth current phase transition during PWM operation for power reduction. Back electromotive force (BEMF) is the mechanical energy that motors provide to do the work of any given application. BEMF is directly proportional to the to the speed of the changing magnetic field as the motor spins, or more simply, BEMF is directly proportional to the speed of the rotating armature. As can be seen in the diagram on this slide, the phase of the current and the voltage generated by BEMF are a function of the motor load. The diagram illustrates the phase difference for a partially-loaded motor. As the motor approaches a fully loaded condition the current and BEMF voltage will actually come into phase.