Bridge Rectifier – Construction, Working, Advantages

The construction of a bridge rectifier is shown in the figure below. The bridge rectifier circuit is made of four diodes D1, D2, D3, D4, and a load resistor RL. The four diodes are connected in a closed-loop configuration to efficiently convert the alternating current (AC) into Direct Current (DC). The main advantage of this configuration is the absence of the expensive centre-tapped transformer. Therefore, the size and cost are reduced.

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The input signal is applied across terminals A and B, and the output DC signal is obtained across the load resistor RL connected between terminals C and D. The four diodes are arranged in such a way that only two diodes conduct electricity during each half cycle. D1 and D3 are pairs that conduct electric current during the positive half cycle/. Likewise, diodes D2 and D4 conduct electric current during a negative half cycle.

Working

When an AC signal is applied across the bridge rectifier, terminal A becomes positive during the positive half cycle while terminal B becomes negative. This results in diodes D1 and D3 becoming forward biased while D2 and D4 becoming reverse biased.

The current flow during the positive half-cycle is shown in the figure below:

During the negative half-cycle, terminal B becomes positive while terminal A becomes negative. This causes diodes D2 and D4 to become forward biased and diode D1 and D3 to be reverse biased.

The current flow during the negative half cycle is shown in the figure below:

From the figures given above, we notice that the current flow across load resistor RL is the same during the positive and negative half-cycles. The output DC signal polarity may be either completely positive or negative. In our case, it is completely positive. If the diodes&#; direction is reversed, we get a complete negative DC voltage.

Thus, a bridge rectifier allows electric current during both positive and negative half cycles of the input AC signal.

The output waveforms of the bridge rectifier are shown in the below figure.

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Characteristics of Bridge Rectifier

Ripple Factor

The smoothness of the output DC signal is measured by a factor known as the ripple factor. The output DC signal with fewer ripples is considered a smooth DC signal while the output with high ripples is considered a high pulsating DC signal.

Mathematically, the ripple factor is defined as the ratio of ripple voltage to pure DC voltage.

The ripple factor for a bridge rectifier is given by

\(\begin{array}{l}\gamma =\sqrt{(\frac{{V_{rms}}^2}{V_{DC}})-1}\end{array} \)

For bridge rectifiers, the ripple factor is 0.48.

Peak Inverse Voltage

The maximum voltage that a diode can withstand in the reverse bias condition is known as a peak inverse voltage. During the positive half cycle, the diodes D1 and D3 are in the conducting state while D2 and D4 are in the non-conducting state. Similarly, during the negative half cycle, diodes D2 and D4 are in the conducting state, and diodes D1 and D3 are in the non-conducting state.

Efficiency

The rectifier efficiency determines how efficiently the rectifier converts Alternating Current (AC) into Direct Current (DC). Rectifier efficiency is defined as the ratio of the DC output power to the AC input power. The maximum efficiency of a bridge rectifier is 81.2%.

\(\begin{array}{l}\eta =\frac{DC\,Output\,Power}{AC\,Output\,Power}\end{array} \)

Advantages

• The efficiency of the bridge rectifier is higher than the efficiency of a half-wave rectifier. However, the rectifier efficiency of the bridge rectifier and the centre-tapped full-wave rectifier is the same.
• The DC output signal of the bridge rectifier is smoother than the output DC signal of a half-wave rectifier.
• In a half-wave rectifier, only half of the input AC signal is used, and the other half is blocked. Half of the input signal is wasted in a half-wave rectifier. However, in a bridge rectifier, the electric current is allowed during both positive and negative half cycles of the input AC signal. Hence, the output DC signal is almost equal to the input AC signal.

Disadvantages

• The circuit of a bridge rectifier is complex when compared to a half-wave rectifier and centre-tapped full-wave rectifier. Bridge rectifiers use 4 diodes while half-wave rectifiers and centre-tapped full wave rectifiers use only two diodes.
• When more diodes are used more power loss occurs. In a centre-tapped full-wave rectifier, only one diode conducts during each half cycle. But in a bridge rectifier, two diodes connected in series conduct during each half cycle. Hence, the voltage drop is higher in a bridge rectifier.

Frequently Asked Questions &#; FAQs

Q1

Choose YES or No: Can rectifiers convert an AC power to a DC power?

YES.

Q2

Define bridge rectifiers.

The bridge rectifier is a type of full-wave rectifier that uses four or more diodes in a bridge circuit configuration to convert alternating (AC) current to a direct (DC) current.

Q3

What is a rectifier?

A rectifier is an electronic device that converts an alternating current into a direct current by using one or more P-N junction diodes.

Q4

State true or false: The bridge rectifier allows electric current flow during both negative and positive half cycles of the input AC signal.

TRUE.

Q5

What is the maximum efficiency of a bridge rectifier?

The maximum efficiency of a bridge rectifier is 81.2%.

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A diode bridge rectifier, also known as a Graetz bridge, is an arrangement of four diodes configured as a bridge circuit that converts alternating current (AC) into direct current (DC). Rectification is the process of converting one form of electrical current (AC) into another form (DC).

Diode bridge rectifiers are widely used in power supplies to convert incoming AC mains voltage to regulated DC that electronic devices can use. They provide full-wave rectification, offer high current capability with minimal power loss, and are cost-effective compared to other rectifier designs.

This article provides a detailed overview of diode bridge rectifiers including:

• How diode bridge rectifiers work
• Bridge rectifier configurations
• Design considerations and calculations
• Performance parameters
• Rectifier diodes and bridges
• Applications and uses
• Pros and cons compared to other rectifier circuits

With the strong demand for efficient and compact DC power conversion, diode bridge rectifiers remain an essential component across industrial, commercial, and consumer electronics.

How Does a Diode Bridge Rectifier Work?

A diode bridge rectifier converts AC into DC using a network of 4 diodes arranged in a bridge configuration. To understand how it works, we first need to examine the properties of diodes.

Diode Current Flow

A diode is an electronic component that allows current to flow in only one direction, blocking reverse current. This unidirectional behavior is depicted in the IV-curve:

Diode IV Curve &#; conducts in forward direction but blocks in reverse

In the forward direction, once the diode reaches its turn-on voltage (typically 0.7V for silicon diodes), current can flow through it. But in the reverse direction, only a tiny leakage current can flow.

Rectification Principle

This unidirectional property of diodes allows them to be used as rectifiers. By only permitting current flow in one direction, alternating current can be converted into direct current.

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Additional resources:
Comparing Carbon Film Resistors and Metal Film Resistors

For example, a single diode can be used as a half-wave rectifier:

Half-wave rectifier uses one diode to block the negative waveform portion

Here the diode conducts during the positive half cycle, allowing current to flow to the load. But during the negative half cycle, the diode blocks current in the reverse direction. So pulsating DC is obtained from the incoming AC.

While simple, half-wave rectification is inefficient as current is supplied only half of each AC cycle. Full-wave rectification makes use of the entire sinusoidal waveform.

Bridge Rectifier Operation

A diode bridge utilizes four diodes to perform full-wave rectification:

Diode bridge rectifier schematic

Let&#;s examine how the bridge rectifier works in each half of the AC cycle:

Positive Half Cycle

• The top input node A is positive relative to bottom node B
• Current flows from node A through D1 and D2 to the load
• D3 and D4 remain reverse biased and block current

Negative Half Cycle

• The bottom input node B is now positive relative to node A
• Current flows from node B through D3 and D4 to load
• D1 and D2 are reverse biased and block current

So in both halves of the AC cycle, two diodes always conduct to permit full-wave rectified current to the load. The alternating polarity of the AC voltage combined with the polarity switching of the conductive diodes results in a DC voltage output.

Bridge Rectifier Configurations

Bridge rectifiers are available in different electrical configurations:

Single Phase

A single phase bridge rectifier is the most common type, converting single-phase AC into DC. It uses four diodes arranged in a Wheatstone bridge configuration fed by a single phase AC supply:

Single phase input bridge rectifier schematic

Single phase rectifiers are suitable for applications powered by standard 120V or 240V AC mains supplies.

Three Phase

For higher power applications, three phase AC input can be rectified using a three phase bridge rectifier:

Three phase input bridge rectifier

Three phase rectification is commonly used in industrial equipment, HVAC systems, motor drives and other machinery using three phase motors or transformers.

Polyphase

For very high power applications, polyphase rectifiers can be constructed using multiple three phase diode bridges connected to multiple sets of three phase inputs from transformers:

Polyphase rectifier with multiple 3-phase inputs (Image credit: ResearchGate)

Polyphase rectifiers help convert very high power levels in the multi-kW to MW range for heavy industrial applications.

Full-wave Center Tap

A full-wave center tap rectifier uses two diodes and a center tapped transformer secondary to achieve full-wave rectification:

Full-wave center tap rectifier

This configuration can save cost over a bridge rectifier when a suitable center tapped transformer is already available. But the peak inverse voltage on each diode is twice that of a regular bridge rectifier.

Bridge Rectifier Design Considerations

Some key design factors and calculations for diode bridge rectifiers include:

Input Voltage

The maximum expected AC input voltage determines the PIV rating required for the rectifier diodes. Generally diodes with PIV ratings at least 1.5 to 2 times the peak input voltage are chosen.

Output Voltage

For a single phase bridge rectifier with purely resistive load, the output voltage is approximately:

$$V_{DC} = 0.9 V_{AC_{RMS}}$$

The output is a pulsed DC value averaging 0.9 times the RMS AC voltage. Capacitive filtering is needed to smooth this into steady DC.

Output Ripple Voltage

Some AC ripple remains on the DC output due to incomplete smoothing. For a full-wave rectifier with capacitor filter, ripple voltage can be approximated as:

$$V_{ripple} = \frac{1}{2fCR}$$

Where f is AC frequency, C is filter capacitance and R is load resistance. Larger capacitors reduce ripple.

Efficiency

Bridge rectifier efficiency can reach over 90% as only small voltage drops occur across forward-biased diodes. Efficiency is highest with high load current when diode forward voltage drops become negligible.

Thermal Design

Each diode must be adequately sized to handle the current without overheating. Heat sinks may be needed on the diode cases for high current applications.

Reverse Recovery

For high frequency AC inputs, snubbers may be required to suppress reverse recovery transients from non-ideal diode switching behavior.

Proper component selection, transformer design, and filtering ensure the bridge rectifier circuit can successfully convert the incoming AC supply into a stable DC output.

Bridge Rectifier Performance Parameters

Key performance characteristics to consider for diodes and diode bridge rectifiers:

• Peak Inverse Voltage (PIV) &#; Maximum reverse voltage the diode can withstand without breakdown. Must exceed peak AC voltage.
• Maximum Forward Current &#; Continuous DC forward current rating, set above expected load current.
• Forward Voltage Drop &#; Around 0.7V for silicon diodes results in losses during conduction.
• Maximum Reverse Leakage &#; Minimal reverse current prevents transformer saturation.
• Switching Speed &#; Fast transitions between forward and reverse states.
• Temperature Rating &#; Typically 50 to 150°C for rectifier diodes and bridges.
• Peak Surge Current &#; Ability to withstand momentary spikes from inrush or transients.
• Heat Dissipation &#; Often set by thermal resistance from junction to case.

For high performance in demanding applications, Schottky diodes offer faster switching speeds and ultra low forward voltage drops compared to standard rectifier diodes. But at increased cost.

Rectifier Diodes

Various diode types can be used in building bridge rectifiers. Let&#;s examine some of the most common.

Power Rectifier Diodes

Purpose-built for rectifier applications, these provide controlled breakdown and fast recovery times at high PIV ratings and forward currents. Come in axial leaded or hockey puck shapes for mounting to heat sinks. Offer lower cost than precision signal diodes.

1N power rectifier diode example

Popular manufacturers include ON Semiconductor, Diodes Inc., Microsemi, and IXYS.

Ultrafast Recovery Diodes

Extremely fast switching speeds with reduced recovery time makes these well suited for high frequency rectification. Low reverse recovery current minimizes EMI. Often used in switched mode and SMPS power supplies.

Vishay 1N ultrafast signal diode

Manufacturers include STMicroelectronics, Vishay, Microsemi, Diodes Inc.

Schottky Diodes

Utilize a metal-semiconductor junction that achieves much lower forward voltage drop (0.15 &#; 0.4V) compared to PN junction diodes. Their fast switching and low losses make Schottky diodes ideal for rectifier applications.

Schottky diode symbol

Key Schottky diode vendors are Rectron, IXYS, Microchip, Diodes Inc.

Rectifier Diode Packages

Diodes used for bridge rectifiers are available in through-hole and surface mount packages:

Through-Hole Packages

• Axial Lead &#; DO-4, DO-5, DO-7 glass or plastic axial leaded diodes for insertion into PCB. Allow heat sink mounting.
• Hockey Puck &#; Large aluminum cases mount to chassis and heat sink. For high current applications.

Surface Mount Packages

• MELF &#; Small plastic molded package soldered directly to PCB.
• SMC &#; Plastic surface mount case with smaller footprint than axial.
• DPAK &#; Injection molded plastic with exposed metal pad for heatsinking.

Axial leaded diodes allow simple construction of prototyping breadboard rectifiers. But SMD packages facilitate automated production and miniaturization of rectifier circuits.

Full Wave Bridge Rectifiers

For convenience, diode bridges are available as standardized pre-packaged modules housing all four rectifier diodes internally with labeled connector pins. These provide quick plug-and-play rectification without needing to individually wire discrete diodes.

Common package types include:

Plastic Case &#; Epoxy encapsulated plastic housing suitable for lower power levels. Manufacturers frequently use PB and KB series designators for these economy plastic bridges.

Small plastic case bridge rectifier

Metal Can / Hockey Puck &#; Metal casing with mounting hole for heat sinking rectifiers. Capable of high currents and heat dissipation. Often marked MR series by manufacturers.

Metal can rectifier bridge

PCB Mount &#; Miniature SMT package bridges allow direct mounting onto PC boards. Low cost, limited current. Marked GBU, SKB, MDA series.

PCB mount bridge rectifier

Other Packages &#; Single in-line (SIP), stacked SIP, large stud mounted modules, press-fit pins.

Bridge rectifier modules with multiple built-in diodes offer standardized drop-in rectification up to tens or hundreds of amps and thousands of PIV.

Bridge Rectifier Manufacturers

Some leading manufacturers of bridge rectifiers include:

• Diodes Incorporated
• ON Semiconductor
• Microchip
• Microsemi
• Shindengen
• Vishay
• IXYS
• Central Semiconductor
• Rectron
• Taiwan Semiconductor
• Comchip Technology

Diodes Inc, ON Semi, Vishay and Fairchild are among the most recognized and largest suppliers. But many other manufacturers also offer rectifier bridges and Schottky diodes for power supply applications.

A wide selection of bridge rectifier specifications is available off-the-shelf through electronics distributors like Digi-Key and Mouser for prototyping or production.

Applications of Bridge Rectifiers

Bridge rectifiers are extensively used in many electronic and electrical systems wherever conversion of AC to DC is needed, including:

• Power supplies &#; Rectify the mains AC input to create the raw DC for power supply systems. Used in everything from wall adapters to high end servers and telecom racks to provide conditioned DC for downstream conversion.
• Motor drives &#; Convert AC power into DC for subsequent inversion back to PWM controlled AC to drive motors at variable speeds. Help enable high performance motor drive systems.
• Battery chargers &#; Rectify line voltage AC into suitable DC for charging lead acid or lithium ion batteries. Allow efficient charging from the AC mains.
• Welders &#; Change the incoming AC into smoother DC with limited ripple for arc welding equipment. Prevents irregularities in the weld current.
• Plating &#; Systems for chrome plating, anodizing or other electrochemical surface treatments require DC. Bridge rectifiers convert plant AC power into suitable DC plating current.
• HVAC &#; Rectify power for heating elements, fans and ventilation equipment from AC sources. Essential to HVAC gear.
• Alternative energy &#; Used to rectify output of some solar, piezoelectric, dynamo, and other transducers that produce AC into usable DC.

Bridge rectifiers enable reliable and efficient AC-to-DC conversion at power levels from milliwatts to megawatts for this wide array of applications.

Pros and Cons of Bridge Rectifiers

Some key advantages and disadvantages of bridge rectifier circuits:

Advantages

• Full-wave rectification doubles utilization of the AC cycle versus half-wave rectification.
• Only a single small voltage drop occurs through diodes so efficiency can surpass 90%. Much less power loss compared to other rectifier circuits.
• Does not require center tapped transformer so simpler transformer construction.
• Capable of very high currents with paralleled diode bridges.
• Low complexity and inexpensive implementation with just 4 diodes.

Disadvantages

• Produces uneven pulsed DC requiring large filtering capacitors or chokes.
• Most basic form lacks regulation so output varies with input and load.
• Generates more ripple voltage at double the input frequency compared to center tap design.
• Not suitable for high frequency inputs without snubber networks.

Overall, the combination of simplicity, full-wave utilization, high efficiency, and low cost makes diode bridge rectifiers a favored choice for converting AC to DC in medium to high power applications.

Comparison to Other Rectifier Circuits

Half Wave Rectifier

Half-wave rectification only uses one diode and blocks the negative half of the AC wave. While very simple, it results in high peak inverse voltage on the diode and poor utilization of the AC input. Bridge rectifiers offer far better performance.

Full Wave Center Tap Rectifier

A center tap transformer and two diodes can also achieve full wave rectification. But the diodes must withstand twice the PIV rating and a center tap transformer is required. The bridge rectifier avoids these issues for usually lower complexity and cost.

Voltage Doubler

For low current applications, a voltage doubler circuit can double the DC output for a given AC input. But voltage doublers require higher component count and large pulsating output that is less desirable for many applications compared to bridge rectifiers .

Synchronous Rectifiers

For very low voltage drops, synchronous rectifier circuits using MOSFETs instead of diodes are used. But complexity and cost is much higher. Bridge rectifiers offer the best balance of cost, simply and efficiency for most medium to high power rectification needs.

Conclusion

In summary, diode bridge rectifiers provide full-wave rectification of AC into pulsating DC by using four diodes switched alternately

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