Diode, Half, and Full Wave Rectification or AC to DC Conversion

We learned about the function of diodes from the previous Diode Introduction article. As we know, a diode is an electronic device that allows the charge or electricity of a certain religion to go only in a certain direction.

PN Junction and Biasing

The diode basically has two sections. If we divide it into two halves, there are some positive charges on one side and some negative charges on the other side. If we add the negative end of the battery to the positively charged end of the diode and the positive end of the battery to the negative end of the diode as shown in the first figure below, the negative end of the battery will be negatively charged to the battery and the negative end of the battery will be negative to the battery. As a result, the layer between the two ends of the diode will increase and the current will not flow. But if we add the positive end of the battery with the positively charged end of the diode and the negative end of the battery with the negatively charged end of the diode as shown in the second figure, the positive and negative charges will accumulate in the battery. As a result, these charges will start coming toward each other and the width of the layer between the positive and negative charges of the diode will continue to decrease.

Thus at some point, its amplitude will disappear and electricity will flow through the diode. We call it forward bias as the current can flow in it. And if not, I call that connection reverse bias.

We call the end of the diode that has a positive charge P and the end that has a negative charge N. However, when drawing a circuit, we present this PN junction as an image.

If the positive end of the battery is connected to the P end of the diode and the negative end of the battery is connected to the N end of the diode, then electricity can flow. Which we call forward bias. And if the negative end of the battery is connected to the P end of the diode and the positive end of the battery is connected to the N end of the diode, electricity cannot flow. Which we call reverse bias. With this knowledge, we can easily convert AC current to DC. But before that, you need to know about AC and DC currents.

AC and DC current

We know that any electronic connection has at least two connections. One of which we know as positive and the other as negative. But this does not happen in the case of AC current. In the case of AC current, the two wires alternately become positive and negative. Sometimes one is positive and the other is negative, and sometimes one is negative and the other is positive. That’s the way it goes.

But this does not happen in the case of DC current. Here one is always positive and the other is always negative. Change does not happen. In real life, we ​​need both currents. So sometimes AC needs to be DC, and again DC needs to be AC. AC current is better than DC for such low-dissipation power transmission and we are using it. Although modern scientists say high-voltage DC transport is better than AC.

AC currents move in a positive and negative direction like the waves in an image. We call it a full wave to cross a completely positive and a negative path. We will direct this AC wave in two ways.

• Half-wave Rectification.
• Full wave Rectification.

Half-wave Rectification

Since the S source is an AC voltage source, if the P wire of this wave in the figure is positive, then the Q wire will be negative. But since a full wave has both positives and negatives, once in a full wave the P wire will be positive, the Q wire will be negative and once again the Q wire will be positive and the P wire will be negative.

Notice in the figure, when only the P wire is positive and the Q wire is negative then the diode is in the forward bias and passing that part of the wave. But when the P wire is negative and the Q wire is positive then the diode is in reverse bias and cannot pass that part of the wave. So we are always getting positive current from point A and always negative current from point B. Then we get DC from AC. But since we get only half of each full wave, we call it half-wave unidirectional. Again this is but pure DC. Although the positive and negative edges are different, the voltage is getting higher and lower. That’s why we call it pulsating DC.

Full wave Rectification

Now if we connect the circuit as shown below when the P end is positive and the Q end is negative then diodes D1 and D2 are in forward bias between the four diodes. As a result, the current is flowing and getting a positive current at the A end of the resistor and a negative current at the B end. Similarly when the P end is opposing and the Q end is positive then d3 and D4 of the four diodes are in forward bias. As a result, electricity is flowing and again we are getting a positive current at the A end of the resistor and a negative current at the B end.

So for both sides of the full wave, we get a positive current at the end of A and a negative current at the end of B. That means we are getting pulsating DC voltage.

Thus using diodes we can convert AC current to DC. However, the DC we got is not pure DC. We got pulsating DC. In the next article, we will make this pulsating DC a pure DC.

Pulsating DC to Pure DC Conversion

Supposed you eat three meals a day for eight hours a day 8 am, 2 pm and 10 pm 8 pm You have enough food in front of you at mealtime and you can eat as much as you want So we can say, these three times a day you are at the peak point of food ৷ So what will happen to you in the middle of it? Surely you will feel hungry or your food needs will be created That means you’re going to the food peak point three times a day, and you’re slowly going down again This is creating a fluctuation of hunger in you. We can think of it as a lot of pulsating DC current Which we got when we went from AC to DC with a rectifier.

In the case of pulsating DC current, the voltage similarly passes as a wave through zero and positive peaks. Now, if you want, you can bridge the gap between this peak and zero points of food. When you have a lot of food in front of you at 8 in the morning, he took some food from there to keep with you Then when the food is removed from in front of you, you will eat these foods By doing this, the fluctuation of your food will no longer exist Then, at two o’clock in the afternoon, when you get food again, put some food back in the bowl, which you will eat before 10 pm. By doing this you will be linear in terms of food and appetite Which we can think of DC current 7. 

There is no fluctuation in DC current We get this as a little moving line You can get pure DC current from pulsating DC just like you used to eliminate this fluctuation by freezing food. For that, when you are at the peak point of the current, you will save some charges You will leave these accumulated charges where the voltage of the pulsating DC decreases Then those points will also come closer to the peak point When you get the peak point of voltage again, recharge the charge and release if necessary. 

If you can accumulate a large amount of charge, those points will be equal to the peak point ৷ in electronics this accumulation is done using a capacitor. A capacitor is an electronic device that can be used to charge and discharge. Again, its special feature is that it can accumulate charge in a very short time, it can also drop the charge In this way we can achieve pure DC current by eliminating any kind of fluctuation including pulsating DC in electronics by using capacitors of suitable capacity as required.

Edited
Jeion Ahmed
Chittagong, Bangladesh