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What Bridge Rectifier Circuit Consists of?

Author: Apogeeweb
Date: 8 Jun 2021
 2460
full wave rectifier waveform

Introduction

A stable power supply is necessary for normal operation of the electrical system. Except for the use of solar cells or chemical batteries in certain special occasions, the direct current of most circuits is converted from the alternating current of the grid. The bridge rectifier is commonly used to convert AC into DC, which is the most commonly used circuit that uses the unidirectional conductivity of diodes for rectification. There are many types of bridge rectifiers: flat, round, square, bench-shaped (plug in and SMD), etc., having GPP and O/J structures. The maximum rectified current ranges from 0.5A to 100A, and the maximum reverse peak voltage ranges from 50V to 1600V.

What is Bridge Rectifier?

Catalog

Introduction

Ⅰ Bridge Rectifier Diode Circuit

Ⅱ Bridge Rectifier Circuit Features

Ⅲ Single Phase Rectification vs Three Phase Rectification

3.1 Single Phase Bridge Rectifier Circuit

3.2 Three Phase Bridge Rectifier Circuit

Ⅳ Role of Bridge Rectification

Ⅴ Bridge Rectifier Wiring Diagram

Ⅵ Difference between Bridge Rectifier and Full-wave Rectifier Circuit


Ⅰ Bridge Rectifier Diode Circuit

The bridge rectifier uses four semiconductor diodes to be connected in pairs. When the positive half of the input sine wave is turned on, the two tubes are turned on, and the positive output is obtained; on the contrary, when the negative half of the sine wave is input, the other two tubes are turned on. Since the two tubes are reversely connected, the output is still the positive part of the sine wave. In addition, the utilization efficiency of the input sine wave by the bridge rectifier is twice as high as that of the half-wave rectifier.
The rectifier bridge stack is generally used in a full-wave rectifier circuit, and it is divided into a full bridge and a half bridge. The full bridge is composed of 4 rectifier diodes connected in the form of a bridge full-wave rectifier circuit and packaged as a whole. The half bridge is to seal the half of the two diode bridge rectifiers together. Two half bridges can form a bridge rectifier circuit, and a half bridge can also form a full wave rectifier circuit with a center tap of the transformer. When choosing a rectifier bridge, the rectifier circuit and operating voltage must be considered carefully.
The forward current of the full bridge has various specifications such as 0.5A, 1A, 1.5A, 2A, 2.5A, 3A, 5A, 10A, 20A, 35A, 50A, etc. The withstand voltage (the highest reverse voltage) is 25V, 50V, 100V, 200V, 300V, 400V, 500V, 600V, 800V, 1000V, etc.
In this chapter, the rectifier diode is regarded as an ideal component, that is, its forward conduction resistance is considered to be zero, and its reverse resistance is infinite, because of the convenience of analyzing the rectifier circuit. However, in practical applications, it should be considered that the diode has internal resistance, and the output amplitude of the waveform obtained after rectification will be reduced by 0.6~1V. When the input voltage of the rectifier circuit is large, this part of the voltage drop can be ignored. On the contrary, if the input voltage is small, for example, if the input is 3V, the output is only 2V, and the influence of the diode forward voltage drop needs to be considered.

Current Direction of the Bridge Rectifier Circuit

Current Direction of the Bridge Rectifier Circuit

Figure 1.

In the positive half cycle of u2, D1 and D3 are turned on, D2 and D4 are turned off, and the current returns from the upper end of the TR secondary to the lower end via D1→RL→D3, and a half-wave rectified voltage is obtained on the load RL.
In the negative half cycle of u2, D1 and D3 are off, D2 and D4 are on, and the current returns from the lower end of Tr secondary to the upper end of Tr secondary via D2→RL→D4, and the other half-wave rectified voltage is obtained on the load RL.

 

Ⅱ Bridge Rectifier Circuit Features

(1) The rectification device used is twice that of full-wave rectification.
(2) Rectified voltage pulse changing direction is the same as full-wave rectification.
(3) The reverse voltage that each device bears is the peak value of the power supply voltage.
(4) The utilization rate of the transformer is higher than that of the full-wave rectifier circuit.

 

Ⅲ Single Phase Rectification vs Three Phase Rectification

3.1 Single Phase Bridge Rectifier Circuit

Single Phase Bridge Rectifier Circuit

Figure 2.

The single phase bridge rectifier circuit is composed of four diodes connected in the form of a bridge. Its disadvantage is that it only uses half a cycle of the power supply, and at the same time the rectification voltage has a large pulsation.
The above Figure 2 (a) shows the direction of current in the single-phase bridge rectifier circuit. The solid arrow indicates the situation when the AC power supply is in the positive half cycle, and the dotted arrow indicates the situation when the AC power supply is in the negative half cycle.
It can be seen that the four diodes are divided into two parts: positive half cycle and negative half cycle. However, the current direction on the load does not change. This is full-wave rectification. In addition, the single-phase bridge rectifier circuit can be implemented with an integrated device "bridge stack" in practice.
In Figure 3. shows the waveform diagram of the single phase bridge rectifier circuit. According to the diagram, the average voltage is: Uo ≈ 0.9U2 (where U2 is the effective value of the output voltage of the transformer secondary side).

wave form (single phase)

Figure 3. Wave Form (single phase)

3.2 Three Phase Bridge Rectifier Circuit

Three Phase Bridge Rectifier Circuit

Figure 4.

The three phase bridge rectifier circuit is developed from a uncontrolled half-wave rectifier circuit, which is essentially a series connection of a set of common cathode and a set of common anode with three semiconductor diodes.
In addition, the three phase bridge circuit must have two thyristors turned on at the same time, one in the common cathode area and the other in the common anode area to form a loop.

Circuit Analysis Law
The diode with the highest anode potential in the common cathode group is turned on.
The diode with the lowest cathode potential in the common anode group is turned on.

Circuit Analysis Examples
Figure 5. t1 ~ t2

t1 ~ t2

In the common cathode group, the potential at point U is the highest, and V1 is on.
In the common anode group, the potential at point V is the lowest, and V4 is on.
The voltage across the load is the line voltage Uuv.

 

Figure 6. t2~t3

t2~t3

In the common cathode group, the potential at point U is the highest, and V1 is on.
In the common anode group, the potential at point W is the lowest, and V6 is turned on.
The voltage across the load is the line voltage Uuw.

 

Figure 7. t3~t4

t3~t4

In the common cathode group, the potential at point V is the highest, and V3 is on.
In the common anode group, the potential at point W is the lowest, and V6 is turned on.
The voltage across the load is the line voltage Uvw.
...
...

Summery
In a full-wave cycle, it can be divided into 6 intervals, each of which is powered by a pair of phase wires to the load.
In a full-wave cycle, each diode is turned on for one-third of the time (the conduction angle is 120°).
During the 6 periods in a cycle, the voltage of the load can be seen as a periodic change.

 

Ⅳ Role of Bridge Rectification

1. Convert the alternating current generated by the alternator into direct current to power the electrical equipment and charge the battery.
2. Limit the battery current to flow back to the generator to protect the generator from being burnt out by the reverse current.

Bridge Rectifier AC to DC Flow Chart

Figure 8. Bridge Rectifier AC to DC Flow Chart

Ⅴ Bridge Rectifier Wiring Diagram

The bridge rectifier circuit overcomes the shortcomings that the full-wave rectifier circuit requires the transformer secondary to have a center tap and the diode to withstand large reverse voltage, but two diodes are used. With the rapid development of semiconductor devices and low cost today, this shortcoming is not obvious, so bridge rectifier circuits are widely used in practice.
It needs to be pointed out that the diode as a rectifier component should be selected according to different rectification methods and load values. If choose improperly, you may not be able to work safely, or even burn the pipe, causing waste.

Schematic Diagram of Bridge Rectifier Circuit

Figure 9. Schematic Diagram of Bridge Rectifier Circuit

The bridge rectifier circuit can also be considered as a kind of full-wave rectifier circuit. The transformer is connected to four diodes according to the method shown in Figure 9. D1~D4 are four identical rectifier diodes connected in the form of a bridge, so they are called bridge rectifier circuits. Using the guiding function of the diode, the secondary output can be directed to the load even in the negative half cycle. It can be seen from the figure that D1 and D2 lead the current through RL from top to bottom during the positive half cycle, and D3 and D4 lead the current through RL from top to bottom during the negative half cycle. In this structure, if the same DC voltage is output, the secondary winding of the transformer needs only half of the winding compared with the full-wave rectification. However, if the same amount of current is to be output, the diameter of the winding should be increased accordingly.
Because the output voltage of the rectifier circuit contains larger pulsating components. In order to reduce the pulsation component as much as possible, on the other hand, it is necessary to keep the DC component as much as possible to make the output voltage close to the ideal DC. This measure is filtering. Filtering is usually achieved by using the energy storage effect of capacitors or inductors.

bridge rectifier circuit with capacitor

Figure 10. Bridge Rectifier Circuit with Capacitor

In this experimental circuit, capacitor filtering is used, that is, a filter capacitor C is connected in parallel with the load resistance RL. The circuit is shown in Figure 11, and the filtered waveform is as shown in the figure below.

waveform (full-wave)
Figure 11. Full-wave Rectification Filter Waveform

The DC component of the full-wave rectified output voltage (compared to the half-wave) is increased, and the pulsation is reduced, but the transformer needs a center tap, which is troublesome to manufacture, and the rectifier diode needs to withstand high reverse voltage, so it is generally suitable for the low output voltage.

Half-wave Rectification Filter Waveform

Figure 12. Half-wave Rectification Filter Waveform

Half-wave rectification is the most commonly used circuit that uses the unidirectional conductivity of a diode for rectification.

 

Ⅵ Difference between Bridge Rectifier and Full-wave Rectifier Circuit

1) Don't need a center tap on the secondary side of the bridge rectifier circuit transformer, but use 2 more rectifier diodes.
2) The full-wave rectifier circuit uses less than 2 rectifier diodes, but the secondary side of the transformer should be center-tapped.
3) The reverse withstand voltage of the rectifier diode used in the full-wave rectifier circuit is twice that of the bridge rectifier.
4) Rectification and full-wave rectification have different requirements for the number of secondary transformers. The former requires only 1 set of coils, while the latter requires 2 sets.
5) Rectification and full-wave rectification have different requirements for the secondary current of the transformer, the former is twice the latter.

 

Frequently Asked Questions about Bridge Rectifier Circuit

1. What does a bridge rectifier do?
A bridge rectifier provides full-wave rectification from a two-wire AC input, resulting in lower cost and weight as compared to a rectifier with a 3-wire input from a transformer with a center-tapped secondary winding. ... Diodes are also used in bridge topologies along with capacitors as voltage multipliers.

 

2. How does a bridge rectifier convert AC to DC?
Bridge rectifiers convert AC to DC using its system of diodes made of a semiconductor material in either a half wave method that rectifiers one direction of the AC signal or a full wave method that rectifies both directions of the input AC.

 

3. What happens when a bridge rectifier fails?
Without capacitor smoothing, when 1 diode fails open in a bridge rectifier, both voltage and current reduce. With capacitor smoothing, when 1 diode fails open in a bridge rectifier, the voltage remains fairly constant but the current increases.

 

4. Why do we use 4 diodes in bridge rectifier?
The bridge rectifier consisting of four diodes enables full wave rectification without the need for a centre tapped transformer. The bridge rectifier is an electronic component that is widely used to provide full wave rectification and it is possibly the most widely used circuit for this application.

 

5. Why is a bridge rectifier more preferable than a full wave rectifier?
Bridge rectifier is driven by a single winding which carries current both cycles in load. ... Full wave is better than bridge in one more aspect i.e. the output DC voltage is slightly higher than bridge. This is because it has only 1 diode drop from AC to DC.

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