Protection systems are the unsung heroes of most electrical systems. They make sure that a fault doesn’t adversely affect an electrical system from performing satisfactorily and guarantee that the faulted equipment is isolated from the rest of the network. This, in turn, ensures the safety of the equipment and, more importantly, the circuit designer working on the project.
One of the most common mistakes people when plugging in electronics is connecting devices with incorrect polarities. While swapping the positive and negative terminal of your device may not seem like a big deal at first, it’s worth noting that reverse polarity can destroy your electronic equipment.
Protecting Against Reverse Polarity:
Given the fact that reverse polarity is such a common problem, circuit designers have come up with a simple yet ingenious solution; diodes! For those of you who don’t know, a diode is a semiconductor that consists of two terminals, namely the positively charged anode and the negatively charged cathode.
How Can A Diode Shield Against Reverse Polarity?
The most commonly asked question about using diodes as protective devices is how can a simple, two-terminal device shield against reversed polarity current? Well, to understand that, we must first understand how diodes work.
As mentioned above, diodes have two terminals (one positive and the other negative). Now when a battery is connected across a diode such that the positive terminal is connected to the positive terminal of the diode, and the negative terminal of the battery is connected to the negative terminal of the diode, the diode is said to be forward biased.
This essentially means that the current passes through the input terminal of the diode and appears at its output terminal. In other words, the diode conducts when it is forward biased.
On the other hand, if the battery is connected across a diode such that its positive terminal is connected to negative terminal of the diode and the negative terminal of the battery is connected to the positive terminal of the diode, the diode is said to reverse biased.
This is where things get interesting. Unlike forward bias where a diode conducts current, a reverse biased diode does not conduct electricity. In other words, the diode prevents the current from flowing through it when its reverse biased.
Owing to this behavior of diodes, circuit designers commonly use diodes to shield against reverse polarity. In other words, when there’s a mismatch of polarity (between the source and the circuit), the protective diode gets reverse biased and does not conduct electricity.
Furthermore, the protective diode isolates the rest of the circuit from this reverse current. Therefore, by using a simple and inexpensive diode as a protective device, electrical engineers can isolate and protect the rest of the circuit (which undoubtedly is costlier).
And that’s how thousands of dollars worth of electrical equipment can be protected using a single diode. We hope that this clears up any confusion you may have had about how diodes operate and why they’re used as protective devices.
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