Diodes allow current to flow in one direction

This is just a short description of why it’s a good idea to add an LED parallel to the DC motor in your circuit. This is a supplementary post for the previous posts, “Transistor Current Amplifier Circuit” and “

“Protecting the DC Motor”

current amplifier circuit controlling motor with LED diode parallel prevent motor damage

The DC motor used in this post might not be worth saving, but say if you were using a really expensive one for a school project then adding some protection to your circuit may seem worth your while.  In the above picture, you will see I have an LED diode in parallel with the DC motor.  Now diodes have parity and only allow current to flow in one direction.  This way it guarantees the current only flows one direction for the LED and for the motor as well because they are connected in parallel.

You may think if you just connect everything correctly it’ll be fine and current should go where it’s suppose to, but it’s when you turn off the power that might damage the motor.  Like taking out the batteries and cutting the power supply to the circuit.  In that instant, current stops flowing, like turning off the water when your parents are watering the garden with a hose.  The water supply stops flowing after 1/2 a second you turn off the water.  It’s the same thing with current.  It takes a very very very short time after you unplug the batteries for the shortage to reach the motor and LED.  You may not see it because electrons move a lot faster than water.

So, while the motor is running with power, there is enough current flowing in and flowing out.  When you cut the power, the motor suddenly has current flowing out, but no more current flowing in.  This difference between the two sides of the motor may damage the motor.

“Back EMF”

When you turn off the hose, water stops flowing, but due to the lack of pressure some water may get stuck in between the pipe.  It may even flow backwards (just a bit, like drops maybe) and you may see some dripping on the connector of the head of the hose.  Now it isn’t exactly the same thing in electron world, but you can see that without the pressure pushing electrons all the way from one end to the other end, some mischievous electrons may stick to the motor and cause a spark inside the commutator causing slight damage to the motor.  The motor would most probably survive a long time even without the diode protecting it from this spark, but if you have a on/off switch then you’re probably going to use it a lot.  And over time, it will wear it down slowly.  Besides diodes are pretty cheap so it’s an extra safe back, so why not.

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