5 Tips for Good Linear Power Supply Design

September 18, 2019 , in Blog

I, for one, am very excited about the increased advances in self-driving cars. There are a number of good general reasons to welcome this innovation to our highways, such as reducing the number of accidents, reducing the stress associated with driving, and reclaiming travel time to do other things. However, I have a more practical reason, as well: eliminating the prospect of getting a speeding ticket, which probably ranks high on the list of ways not to get your day off to a good start. The best autonomous cars, with features like adaptive cruise control (ACC), which maintains the best speed irrespective of changing road conditions, should make that possibility a thing of the past.

Power supply circuit board

Power supply PCB

Just as maintaining the best speed is important on the road, maintaining a consistent output is important when designing power supplies. In fact, it is not just important, but mandatory. Failing to do so can result in erroneous operation and circuit failures throughout your system. Regulated linear power supplies are one of the most successful circuits for providing a constant output voltage, provided they are used for the right applications and designed well. Following a few tips can ensure that you create a good linear power system design that is manufacturable. But, before we get to those, let’s make sure that we know where and when it is best to use a linear power supply.

Linear Power Supplies: Usage and Applications

Linear power supplies are most often used to convert a mains AC voltage to a lower level DC voltage for electronics. Typical conversions are from 120V@60Hz or 220V@50Hz down to 24V or 5V DC. Additionally, linear power supplies are used to drive embedded products and equipment in industrial facilities. Common types of systems, which include linear power supplies are:

  • Communications
    • Signal processing
    • Data acquisition
    • Amplifiers
  • Laboratory test equipment
  • Control circuitry
  • High power industrial equipment

Linear power supplies tend to be bulky and somewhat inefficient, as compared to switch-mode power supplies (SMPS). However, they have the advantage of low noise, which is due to the minimal use of switching devices that is an attribute of SMPS and fairly simple to design.

How to Achieve a Good Linear Power Supply Design

When designing linear power supplies for operation, the most important factors are: range of inputs (voltage, current and frequency); conversion rate (typically, the turns ratio of a step-down transformer); common-mode rejection ratio (CMRR, the ability to reject noise between the output voltage and ground); isolation between the source and the power supply circuitry; ripple voltage (the difference between the peak and average value of the output voltage); ripple frequency (residual frequency variation after rectification); and the output current range (minimum to maximum current that your load will draw). In order for a board to be built to achieve meet these objectives, your linear power supply must also be designed with manufacturing considerations. Following the tips below will ensure that your board can be built and meet your design specifications.

Tips for Linear Power Supply Design for Manufacturing

Tip #1: Use the smallest package possible

If you are designing a power supply board, then you should make the PCB layout as small as possible. If you are choosing a power supply for your board, then you should select the smallest package that meets your specifications.

Tip #2: Ensure traces can carry current capacity

As the amount of current is dependent on the load and variable, it is critical to ensure that the trace width and copper weight are sufficient to handle the current regardless of the load conditions.

Tip #3: Route efficiently

When laying out your board, it is important to apply the best routing techniques. Objectives should to minimize losses, use less board space and reduce noise.

Tip #4: Apply good thermal design techniques

For high power circuits, one of the most important design considerations is thermal dissipation. However, for all power supplies, it is important to consider heat dissipation and distribution during manufacturing.

Tip #5: Apply good filtering

Although linear power supplies typically have fewer issues with ripple frequency, they do contain switches for rectification. Additionally, your load circuit may introduce variation into the output signal. Therefore, you should also apply a good power supply filter design to ensure a stable output voltage.

Tempo‘s Custom PCB Manufacturing Service
  • ISO-9001, IPC-600 and IPC-610 commitment to quality certifications.
  • Accurate quote in less than 1 day.
  • Performs entire turnkey process in as fast as 3 days.
  • Emphasizes DFM to eliminate time-consuming back-and-forth design corrections.
  • Sources components from the most reputable suppliers in the industry to reduce procurement time.
  • Performs multiple automated inspections during assembly to ensure PCB quality for prototyping.
  • Provides support throughout the PCB manufacturing process, beginning with design.
  • Smooth transition from prototyping to production.

By following the tips listed above and adhering to the rules and guidelines of your contract manufacturer’s (CM’s) DFM, your linear power supply design will not only meet your operational objectives but also enhance your product development efficiency.

At Tempo Automation, we will get you started on this path by furnishing information for your DFM checks and enable you to easily view and download DRC files. If you’re an Altium Designer or Cadence Allegro user, you can simply add these files to your PCB design software. For Mentor Pads or other design packages, we furnish DRC information in other CAD formats and Excel.

If you are ready to have your design manufactured, try our quote tool to upload your CAD and BOM files. If you want more information on good linear power supply design for manufacturability, contact us.

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