Book Analog Interfacing to Embedded Microprocessors
than with higher loading. However, the controller applies sufficient current
to the motor to produce the required speed/time curve regardless of motor
load. For this reason, DC motors are usually better for applications with large
load variations.
One feature of DC motors is the ability to brake them. If you manually turn
the shaft of a DC motor, you get a small generator. If you short the terminals
of a DC motor, it becomes difficult to turn the shaft because of the EMF (elec-
tromotive force) that the motor generates when it turns. If you short the
motor terminals while the motor is running, it quickly comes to a halt. This
is called dynamic braking.
Figure 7.21
DC motor operation with different loads.
182 Analog Interfacing to Embedded Microprocessors
Figure 7.22 shows the H-bridge we’ve looked at before, but with a modifi-
cation. Here, we have separated the motor control inputs so we can turn each
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