Electrical Learning || Part 04 || How diodes work, why they are used, and how to identify good and bad diodes.

How are you all? I hope you are well. By the grace of God, I am also well. Today we are going to talk about diodes. The diode is one of the most important components behind the advancement of electronics. Almost all the different types of electronic devices that we use every day are DC-powered. Converting DC power to AC requires converting AC to DC current. And this work is done through diodes. Today we will discuss what types of diodes are and what diodes are used for and how they work. And what is forward bias and reverse bias, and how to test a diode.

The main function of a diode is to allow electricity to flow in one direction and to block the flow of electricity in the other direction. The diet usually has two terminals. The terminal on the left side of the diode is the anode, or positive terminal, and the terminal on the right side is the cathode, or negative terminal. The way to identify the positive and negative terminals of the diode is the silver-colored spot on it. The side on which this stain will be is the negative side. And its opposite side is the positive side, anode site.

The number we see next to the silver color spot indicates the specification of the diode. That is, if you search this number on Google, you can find how many volts the diode works, how many amperes, etc. Various detailed information is available with this number. The symbol we can see on the screen now is the diode symbol.

Diodes are generally of many types. general diode, Zener diode, tunnel diode, light-emitting diode, sohottky diode, laser diode, photo diode. Symbols are given in the middle, and their actual images are given on the right side.

Well, let's first see a practical example of how a diode works. Here a battery is charged by connecting it to a charger. Now the current is going from the 5 volt charger to the 3.7 volt battery and charging the battery. Because electricity always flows from high voltage to low voltage. Now we unplug it from the socket, but the charger indicator is still on. Because 3.7 volts of current are flowing from the battery to the charger. If this continues for a long time, the battery will run out of charge, so what is the solution?

If we put a diode in this line in reverse bias with respect to the battery, then the electricity will not go to the charger. And the current can flow directly from the charger to the battery.

Today, the chargers or devices we use have built-in diodes. Earlier devices and earlier chargers did not have this system. A diode is usually connected in a circuit in two ways, or we can say it works in two ways. One way is forward bias, and the other is reverse bias.

Connecting the positive terminal of the diode to the positive terminal of the battery or power supply and the negative terminal of the battery or power supply is called forward bias. And current can flow through the diode, as we can now see on the screen. Here the current from the battery is going through the diode to the light, and that is why the light is on; this is the forward bias of the diode.

Now we see what actually happens during forward bias or how forward bias works. Here's an animation comparing a diode to a one-way bulb. We can see that there is a door in the middle of this tube that opens when the current from the battery is trying to flow through the diode, and the current flows through the diode very nicely.

A minimum voltage of 0.7 is required here; it is called the forward bias volt. If made of silicon, then the forward bias voltage will be 0.7 volts. If the diode is made of germanium, then the forward bias voltage will be 0.3 volts. Any voltage below 0.3 or 0.7 volts will not open this door. So no current below 0.3 or 0.7 volts will flow through the diode. But currents above 0.3 or 0.7 volts can flow.

Reverse bias and forward bias are the opposite. Reverse bias is connecting the positive terminal of the diode with the positive terminal of the power supply and the positive terminal of the diode with the negative terminal of the power supply. Current cannot flow through the reverse bias diode, so we see the light now off. Well, let's try to understand reverse bias with a little animation. We're back to the biased bucket, but this time we've connected direct reverse bias to the battery. We can see that when electricity passes through it, the door closes and no current can flow. And the light is off because the current is not flowing.

But in reverse bias, if we increase the voltage, then the gate will not be able to withstand the pressure of the voltage, and the gate will break. Then too much current will flow through the diode very quickly, and the light will also be destroyed due to the excess current flowing. That is, if the capacity of the diode with the power supply is not high, it will burn out. And at this time, due to the diode being burned and damaged, the pressure at which its door was broken is called reverse bias breakdown voltage. Which is around 1000 volts for a normal diode.

If you have a digital multimeter, you can do the diet test with that. I have a digital multimeter, and I am showing it. First, turn the selector k of the multimeter to the diode continuity test mode. Now test and see if there is any beep sound; if there is a beep sound, then it is broken. And if the beep sound does not come, then the diode is good.

First there was no sound in forward bias; now we checked reverse bias and saw that there was no sound, which means the diode is good.

But just by doing a test, it is not possible to tell whether the diode is good or bad, so I clicked the selector button of the meter and set it to diode test mode from continuity; now I see what the reading is. This value is between 0.400 and 0.600 for good diodes, showing here 0.560.

Now let's check the reverse bias. We see the meter showing 0.0 reading in case of a good diode; no reading will come; we have this diode is good.

Let me summarize: in a good diode, reverse bias or forward bias, any connection will not give continuity. And reverse bias will show no value.

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🟩 Thank you for reading my post and giving your valuable time. Stay well and stay healthy. God bless you. 🟩

Photography Details

📱Edited with Canva.	Edited with Canva.
📍Location	Narayanganj, Bangladesh
📷Edit by	@imranhassan

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