Bridge Diode

To understand Bridge Diode

The explanations of Bridge Diode found on the net are more or less the same. But I wonder how many common people understand. Before seeing the Bridge Diode function we see Center Tap (Transformer) type full wave rectifier, where two diode are used with a transformer.

Center Tap (Transformer) - Wiki 
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Common applications of center-tapped transformers

A full-wave rectifier using two diodes and a center tap transformer.

The above is the typical rectifier circuit by using center-tapped transformer.

 

sptt

The sine wave is misleading as the horizontal line is time. If you think the place at the top of the secondary winding, at the left side of D1 the voltage changes 0 -> + peak -> 0 with respect to the center tap (which we can say "neutral") during the first half cycle.

Meanwhile at the same time ( the first half cycle period) if you think the place at the bottom of the secondary winding, at the left side of D2 the voltage does not change and remains change with respect to the center tap

 

Then during the 2nd half cycle if you think the place at the bottom of the secondary winding the voltage changes 0  -> + peak -> 0.

 

Then you can get the above right hand picture showing the upper part of the sine waves

 

Bridge Diode

Wiki

Rectifier

wiki 

In the diagrams below, when the input connected to the left corner of the diamond is positive, and the input connected to the right corner is negative, current flows from the upper supply terminal to the right along the red (positive) path to the output and returns to the lower supply terminal through the blue (negative) path.

 sptt

This explanation is misleading or even incorrect. The incorrect part is

the input connected to the right corner is negative,

This should be < still positive but lesser voltage than the left corner of the diamond (which is positive). The current still flows.

Please consider the polarity of diode. 

 

The input polarity changes + / - cyclically or sinusoidally.

the input connected to the left corner of the diamond is the voltage change 0 -> + peak -> 0

and then -> - peak -> 0 with time (periodically).

Meanwhile at the same time (period) what happens to the input connected to the right corner of the diamond ?

 

 

wiki

 

When the input connected to the left corner is negative, and the input connected to the right corner is positive, current flows from the lower supply terminal to the right along the red (positive) path to the output and returns to the upper supply terminal through the blue (negative) path.

sptt

 

Again this is incorrect. The incorrect part is

  (the) current flows from the lower supply terminal to the right along the red (positive) path to the output and returns to the upper supply terminal through the blue (negative) path

the blue (negative) path

This should be <still positive but lesser voltage than the right corner of the diamond (which is positive). The current still flows.

 

Again please consider the polarity of diode. 

Then you can get the full wave rectification shown above.

Anyway the above wiki explanation does not say sine wave, just simply the polarity changes at the input.

The following article is fine.

 

https://www.analog.com/en/resources/glossary/full-bridge-rectifier.html

How does a bridge rectifier work?

Since current can only flow in one direction through a diode, current must travel different paths through the diode bridge depending on the polarity of the input. In either case, the polarity of the output remains the same. When there is an AC input, the current travels one path during the positive half cycle, and the other during the negative half cycle. This creates a pulsating DC output since the signal still varies in magnitude, but no longer in direction.

Current flow in a bridge rectifier during the positive half cycle.

Current flow in a bridge rectifier during the negative half cycle.

No <negative> is shown and the polarity of diodes are OK. The current flows from Anode to cathode all the way.

sptt