PCB Layout Bridge Rectifier: Important Design Guidelines

Cell phone chargers are one of the most common uses of electronic rectifiers.

Some may say that love, money, or even coffee make the world go around. Engineers usually lean toward a more scientific answer, such as ‘power makes the world go around.’ There is a strong case for this perspective. Can you imagine what would result if we suddenly were without chargers to power up our cell phones?

Fortunately, we have rectifiers that convert AC to the required DC level to power our products and systems. A typical example of this is converting the 120V/208V or 230V/400V AC from the power mains to the 5V DC necessary for cell phones. Here are several of the topologies available for electrical rectification:

Half-wave
- - One diode conducts for a half-cycle.
  - Simple to design.
  - Low cost.
  - Inefficient.
Full-wave

- - Two diodes for full-cycle conduction.
  - Typically, a transformer is necessary.
  - More constant output than half-wave.
  - Improved efficiency over half-wave.
- Bridge
  - Full cycle conduction.
  - No transformer is required.
  - Smooth, low ripple output.
  - Efficient.
  - Low cost.
Synchronous

- - MOSFETs are used instead of diodes.
  - Requires external control.
  - Complex design.
  - Highly efficient.
Silicon-Controlled Rectifier (SCR)

- - Commonly use thyristors for precise conduction cycle control.
  - Complex design.
  - Very efficient.
  - EMI can be an issue.

All devices above are in power supplies or output control circuits. The design challenge is to select the best rectifier topology for your application, considering the required performance needs and characteristics.

The bridge rectifier is a good general choice for many applications due to its relatively constant (low ripple) output, efficiency, uncomplicated design, and low cost. However, to fully leverage these advantages, good PCB layout bridge rectifier design guidelines are necessary.

Important Design Guidelines for Bridge Rectifiers

Bridge rectifiers owe their moniker to their circuit architecture, an example of which is shown below for the MSB30M bridge rectifier.

Schematic symbol for the MSB30M-13 bridge rectifier.

As illustrated, one two-diode pair (1 and 3) forms a bridge between the input and the output during one half-cycle, while the other pair (2 and 4) forms the bridge for the other half-cycle. Due to its relatively constant DC output, this rectifier configuration is a favorite for linear power supply designs. When designing bridge rectifier circuits, following the layout guidelines listed below is essential:

PCB LAYOUT BRIDGE RECTIFIER DESIGN GUIDELINES
Order	Guidelines	How to Implement
1	Choose the right rectifier	Compare rectifier specs with parametric performance objectives
2	Use a verified CAD model	Source footprints from a trusted online CAD model resource
3	Follow the manufacturer’s layout recommendations	Use manufacturer datasheets for accurate pin connections and special layout instructions such as copper pour areas, etc.
4	Apply ripple minimization techniques	Use properly selected capacitors placed close to the output terminals for filtering and smoothing
5	Keep trace routes short	Place the rectifier close to the input terminals Minimize the length and increase the width of bridge traces
6	Isolate input and output grounds	Use different grounds for AC and DC signals Allow ample room in the plane for clear return paths
7	Design to minimize EMI	Follow industry standard spacing guidelines
8	Employ thermal management design best practices	Use heat sinks and thermal vias Perform thermal simulation
9	Verify operations and performance before sending for board build	Simulate the circuit for the full input range and check output responses

The guidelines above apply to virtually all PCB layout bridge rectifier designs, including the commonly used types below.

BRIDGE RECTIFIER TYPES AND COMMON APPLICATIONS
Types	Common Applications
3ɸ Bridge Rectifier Discrete Diode Rectifier Integrated ฺBridge Rectifier Schottky Bridge Rectifier Fast-Recovery Bridge Rectifier Controlled Bridge Rectifier	Battery Chargers TVs Computers Medical Equipment Detectors Appliances LED Lighting Wind Turbines Arc Welding Equipment HVAC Systems Motor Controllers

Efficient PCB Layout Bridge Rectifier Design

Bridge rectifiers are commonly used components for converting higher-voltage AC to a usable DC level. Bridge rectifier circuits can range from being relatively simple to complex in their design. Consequently, a good understanding of capabilities and functionality is necessary to select and implement the best bridge rectifier for your project.

Regardless of the rectifier used, the best results arise from following the PCB layout bridge rectifier design guidelines described above and relying on a trusted industry leader for manufacturer-vetted CAD models, verified design data, and information.

If you’re looking for CAD models for common components or important PCB layout bridge rectifier design guidelines, Ultra Librarian helps by compiling all your sourcing and CAD information in one place.

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