Inductive
(Electromagnetic) Outputs |
A motor output is inductive as it contains a coil that can generate a high voltage (or "Back e.m.f.") when it is rotating. In a transistor circuit this can damage components. To prevent this, a diode is placed in parallel with the output device. This takes any induced Back e.m.f. voltages from the motor straight up to the power rail and not back to the previous "sinking" transistor stage. (For details on "sinking" see non-inductive outputs).
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Back e.m.f. Protection from a Low Voltage Motor (Note. The 3 volt low voltage motor here would be burnt out if connected straight across the 9 volt power supply. To avoid this, a 22 ohm resistor is connected in series to reduce the voltage dropped across the motor.) |