How to Understand Diodes and Build a Bridge Rectifier

Here we learn the basic working principle of rectifier diodes such as a 1N4007 or a 1N5408, and also learn how to connect 4 of these together to build a bridge rectifier circuit quickly.

Introduction

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.

Diode Pinouts

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.

how to join diodes to make bridge rectifier circuit network


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Comments

Anand Lobo said…
I had a thought which I'd like to run by you.
My boss works with low power home-built three-phase alternators. At the moment, he uses a three-phase diode bridge for the AC->DC conversion, which I am sure you are familiar with.
I presume you are also familiar with active rectification. My thought is:
Would it be feasible to switch the MOSFETs in an active rectifier based on the physical rotation angle of the alternator? For example, with a Hall-effect sensor detecting the magnetic field outside of the spinning alternator, could that work to trigger the MOSFET switching?
Swagatam said…
I am not very sure, it's difficult to imagine the results without practically verifying the set up, however the concept looks feasible and can be tried.
By the way what could be the benefit of driving the active rectifier without a physical connection when it's easily accessible from the motor??
akshay said…
I want to make a bridge diode rectifier circuit to give an output voltage of 350 volts. Please Help.
Swagatam said…
you can make it as per the above instructions.
Prosenjit said…
Please clear my basic conception : AC main line has Phase (live) Line tester glows, and Neutral ( tester does not glows), If i connect Bridge rectifier in Phase & neutral in junction of cathodes of two diode emits Positive Voltage. In positive half cycle of 50hz AC only a single Diode conducting which is forward biased. if no load connected, In negative half cycle other diode of cathode junction conducting.

My doubt is while negative half cycle is the Neutral line of AC converting AC signal to DC. or what ?

Neutral line of AC is not providing +ve what is the purpose of use of 4 diodes.

instead if I connect Anode of one diode in phase line of AC cathode will emit only positive voltage as half wave rectifier.
and if I connect Anode of one another diode in neutral line and Cathode of both diode joining together to get full wave . why not? ( if no load connected) and passing route +ve voltage through a LED and high value resistance to neutral line. Will this work?

Negative half cycle coming from neutral of AC line. ?? Neutral line carries what? or Phase line have both positive and negative half cycle at a 50 times per seconds. ?
if so then why connect with neutral line of Bride rectifier ??

Hope you will clear my basic conception ..As i am new guy tying to understand.
Swag said…
No, sorry your idea will not work, during positive half cycle phase point becomes +220V and neutral is at 0V. During negative half cycles, phase turns into -220V and neutral continues to be at 0V, so in both ways neutral is always at 0V, only the phase changes from +220V extreme to -220V extreme.

For both the cycles the neutral provides the return path, and that's why a bridge rectifier becomes so ideal in this situation, it provides a clear return path to both the +/- 220V potentials through the load.

if we use only two diodes the effective result will half wave due to lack of return path for the negative cycles.

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