Hi, All,
In Arduino starter kit, project 09 Motorized Pinwheel, we have the schematic in attachment.
I'm trying to understand how diode protects the circuit.
In the attached img,
Now, how come diode will let the back voltage/current go through so that I'll protect the circuit?
The voltage reverses, the current through the inductor most definitely does NOT
reverse - it tries to keep going - the diode allows it to keep going with large voltages
being needed. Inductors will generate whatever voltage is necessary if you try
to switch off the current suddenly - that usually means fried components unless
an easy route is provided.
Current goes through, voltage is across (a difference between two points in a circuit).
Thank you for your reply, MarkT.
"Inductors will generate whatever voltage is necessary if you try
to switch off the current suddenly - that usually means fried components unless
an easy route is provided."
==> The voltage could be higher than the original power source, once power is off suddenly, right?
Far higher. The voltage is proportional to the rate of change of current, try to
shut it off fast and the voltage will jump to 100's or 1000's of volts - you'll see sparks
on a mechanical switch for instance.
In equation form
V.dt = L.dI
[ This mirrors the capacitor equation I.dt = C.dV ]
For instance imagine a 100uH inductor with 100mA being switched off in 0.1us,
plug in the values and V = 100V
A large 1H inductor with 10A switched off in 10us gives 1MV - ie it will destroy its own
insulation and the switching device. But such an inductor would be storing 50J,
released in 10us thats megawatts of power (an explosion, basically)
( Energy stored in an inductor is 0.5.L.I^2 )
