Friday, April 5, 2013

How to Understand Diodes and Build a Bridge Rectifier


Diodes are one of the important electronic components used for rectifying an AC into DC. Diodes have the property of allowing DC through a specified direction and rectifying AC across its pin outs. Let’s learn the components more elaborately.
Diodes are tiny electronic components which are normally recognized by their cylindrical black colored body having a white band at the edge of their body. 


They have two pin across the two ends of their body. The pins also called leads are assigned with appropriate polarities termed as the cathode and the anode. The terminal coming out from the banded side is the cathode while the opposite termination is the anode.

The black colored diodes are normally rated at higher amps while the smaller ones which are red in color are much lower with their power rating.

The power rating suggests how much current can be passed across the device without heating up the part to damaging levels.

Diodes have one important function which becomes their sole property. When an alternating current is applied across the anode and the ground of a diode, the output across the cathode and the ground is a direct current, meaning the diode is able to convert an AC to DC through a process called rectification.

How does Rectification in Diodes Take place

We know that an alternating current is made up of a voltage content which is not stable, meaning the voltage and the current flow constantly changes its polarity from zero to the given highest voltage peak, then it falls back to zero, then reverts to the negative polarity and heads toward the negative voltage peak and gradually falls back to the zero mark for repeating yet another similar cycle.

 This repeated change of polarity or the cycles may have a specific tome periods depending upon the frequency of the AC or vice versa.

When the above AC is introduced at the anode of a diode with respect to ground, the negative cycles are blocked by the diode and only the positive cycles are allowed to pass which appears at the cathode of the diode with respect to the ground.

Now if the same AC is applied across the cathode of the diode with respect to the ground, the positive cycles get blocked and we are able to receive a only the negative cycles with respect to the ground.

Thus depending upon the polarity of the diode, the applied AC is effectively rectified such that only a specified voltage appears at the other end or the output of the device.

In case it is required to process both the cycles of an AC for better efficiency and for getting a completely rectified AC, the use of a bridge rectifier is employed.

A bridge configuration is a smart arrangement of four diodes such that the applied AC across the network results in the rectification of both the halves of the AC cycle. 

It means the positive half as well as the negative half cycles are both converted to positive potentials at the output of the bridge configuration. This arrangement results in a better and a more efficient of an AC signal. 

A filter capacitor is normally used at the output of a bridge so that the notches or the instantaneous voltage blackouts can be compensated through the charge stored inside the capacitor and for generating an well optimized and a smoother DC at the output.

Making a Bridge Rectifier Circuit

Making a bridge rectifier using four diodes is not at all a difficult task. Simply by twisting the terminals of the four diodes in a specific pattern, a bridge rectifier can be made within seconds.

The following steps may be incorporated for making a bridge rectifier:

Take four diodes.

Pick two of them and align there banded sides or the cathodes together such that they are held in an arrow like shape.

 Now twist the terminals tightly such that the joint holds the orientation intact. Keep this joined pair of diodes aside.

Now pick the remaining couple of diodes and repeat the above procedure, however make sure now the opposite ends or the anodes go through the above explained steps.

Finally it’s time to fix the final bridge network, which is done by integrating the above two assemblies together with their respective free ends as shown in the figure.

Your bridge rectifier design is ready and may be used for the intended application. 

Alternatively the above explained method of making a bridge can be followed over a PCB also by inserting the diodes in the PCB as per the explained orientations, and by soldering them at the required places.



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