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Whether it was a bipolar transistor or a FET, if a mechanism to overcome this generated current was not put in place, said transistor will not last long.
But why does this happen? Lets take a quick look at what is happening with our inductor. It is a known law of physics that inductors will not tolerate abrupt changes in current either when they are being charged or when they discharge.
This is in essence because as you apply a voltage and a current starts to flow through the conducting element, a magnetic field is generated. The magnetic field at the same time generates a current that fights the incoming current, making the incoming current needing to fight its way into the inductor.
Either way, and at the end of this charging ordeal, we can see that the energy that went into the inductor will be maintained in the form of a magnetic field. Case A of our picture shows a current happily flowing into our inductor.
I say happily because in essence nothing stops this flow. As soon as the FET is energized, the current starts to flow until the inductor saturates.
But what happens when the FET is disabled? This will eventually happen, right? This may be fine except that all the energy stored inside the inductor will now want to get out of its cage, plus the current can not change abruptly so whatever was going in, must continue going out.
But the FET is off!!! This angry current, as portrayed on case B, will not care too much about its path not being present. A path will be made, one way or the other! And as it is often the case, the voltage goes up in such a way that the FET is damaged.
We need to provide a way for this current to find a safe path which not encompasses the destruction of our transistor switch. And the solution often comes in the form of what is called a free wheeling diode.
Notice the diode is placed such that while the FET is on, it can not conduct its voltage from anode to cathode is negative. It is only when the FET is OFF, that the inductor operating as a source makes the voltage across the diode positive, hence making it conduct.
In this case, the FET sees no current flow and no negative voltage. But why do we need to bother about this when dealing with H Bridges? The previous example shows a simple single FET driver. Are H Bridges subjected to the same problems? In essence the problem still exist because inductive loads will still try to conduct through a disabled FET when said switch gets disabled.
So an H Bridge would suffer the same fate as the single transistor driver if an alternate path is not provided. However, the H Bridge has enough alternate paths, and this is where current recirculation or decay modes come into play.
Lets take a look at the H Bridge quickly. It is completely forbidden to enable the two FETs on the same side, as this would lead to Shoot Through a short circuit from power supply to ground.
If the inductive load was say a DC motor, then the motor would spin in one direction, say clockwise. This has the desirable effect of turning the motor in the opposite direction, in this case counterclockwise. Because as soon as you do, then the current will try to keep on flowing on the same direction, which should result in flames right?
Not necessarily… What if we add freewheeling diodes to save the day? Four of them should do, right? As it turns out, we do not need them!As evident by the sheer amount of answers to this question, there are numerous and diverse reasons why startups fail.
"The main thing to do if you want to start a startup is look at what happens to those 9 out 10 startups that don't make it. People have difficulty understanding the motives of people who are involved in abuse.
Why people choose to abuse other people is a common question. Why (adult) people who are being abused choose to stay in abusive relationships is another.
Neither of these questions have easy answers and even the. Writing your goals down is one of the most important actions you can take to obtain the life you want.
Sadly, most people don’t do it.
Here are five why reasons you should. Here's a general outline of the things to do and not to do on r/writing in order to get the most out of our wonderful community.
Please keep these guidelines in mind for all of your posts and comments. Before writing a check, make sure that it’s really something you need to do. Writing a check is cumbersome, and it’s not the fastest way to move money.
Writing a check is cumbersome, and it’s not the fastest way to move money. Points well-made, and I needn’t bother myself with writing down with what I had to say, since you’ve said it all @Shubhrastha. And anyone who thinks Bandit Queen titillated audiences (no matter how depraved the viewer), needs to get a reality check.