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Inductive |
The following outputs are "inductive", as they contain coils or motors. These devices can generate high voltages when they are being switched due to the magnetic fields they create. The voltages are known as "back emf" and being high, can be very damaging to previous components or subsystems if they are not removed. In order to protect the previous subsystem circuit components from back emf, it is important for a diode to be placed in parallel with the output device. This will direct the generated currents away. To make these output devices work properly, they should be sinked by the previous subsystem (see OP1) and some other modifications made to ensure the smooth running of the system.
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First, note how the 4.5 low voltage motor would burn out if it were connected straight across a 9 volt power supply. To avoid this, a 33 ohm resistor is connected in series. This reduces the voltage it sees and works in a similar way to the potential divider circuit in IP1. As mentioned, the diode in the circuit is used to remove any back e.m.f. The induced voltages/currents are taken away from the motor and up to the + power rail. The 0.1 uF capacitor is used to "smooth" away noise generated by the contacts/ brushes in the motor. This can be important as some sensitive circuits may be affected by this. |
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A mechanical buzzer will produce a fixed tone when a voltage is connected across it. In this circuit it needs to be sinked to operate. As some buzzers can generate electrical noise in the circuit and interfere with the working of the previous process subsystem, it is advisable for a diode and capacitor to be added in parallel. This will reduce any unwanted effects. |
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The inductive outputs mentioned here, similarly work by using a coil to generate a magnetic field. As we have seen, it is important to remove any of the generated voltages that occur when the output is switched. Again, the diode and capacitor take care of this. Note how the diode is connected - the band/ line, marked on the diode case, is positioned towards the positive rail connection (as indicated in the circuit diagrams).
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