Power supply noise is a common problem for designers and others involved in the production of electronic products, and it is essential to consider and plan ahead to reduce it. Here are some feasible methods to achieve this goal.
Application Filter
One option with several related possibilities is to use filtering techniques to manage power supply noise. For example, you can use output capacitors to minimize noise because they react to the output impedance of the power supply circuit. However, capacitors have equivalent series resistance (ESR) and equivalent series inductance (ESL). Choosing capacitors with lower ESR and ESL will reduce noise.
However, note that a sharp decrease in ESR (which can be achieved by replacing electrolytic capacitors with ceramic capacitors) can lead to power supply instability, as ESR may provide erroneous signals related to feedback.
In addition, ferrite beads are particularly effective at filtering high-frequency output noise. They dissipate high-frequency noise energy, and this is true over a wide frequency range. However, ferrite beads become resistive within the desired frequency range, and excess noise is dissipated as heat.
Electromagnetic interference (EMI) and radio frequency interference (RFI) filters also aid in noise management because they prevent these types of electrical noise from entering the system and disrupting its function. These filters can also block devices from emitting electrical noise through power lines. This second aspect is important because government regulatory agencies regulate the amount of noise that devices can generate and transmit through AC power lines. Restrictions also differ between North America and Europe.
Clamp filters (also known as ferrite clamps) are another common intervention method, especially in products such as computers or office equipment. These filters have a cylindrical ferrite core embedded in plastic, divided longitudinally into two parts. The main advantage of clamp filters is that you can use them in existing electronic equipment setups without cutting cables. These filters also protect devices from electrostatic discharge (ESD).
Determine the expected operating temperature of the equipment.
Extreme temperatures can damage electronic products and increase power supply noise. However, by combining design considerations with customer education, company representatives can increase the likelihood of user satisfaction with product performance.
For example, a ventilated power supply can help maintain a suitable system temperature, but it is not a suitable choice if people use these products in dusty or humid environments. Furthermore, if the power supply risks overheating and posing a burn risk to the operator, the designer must consider the most effective methods to keep the power supply cool.
Conversely, cold weather increases output voltage ripple and system noise. Low temperatures can also negatively impact the power supply's output regulation capabilities. Electronic products generally perform better in cold temperatures than in hot temperatures, but any extreme temperature will impair device performance.
We advise customers not to operate the product in cold weather to avoid increasing system noise; this is a simple way to reduce noise. In addition, a detailed specification sheet should be provided so that people can easily refer to it when owning or using the product.
Pay attention to PCB design
Printed circuit boards (PCBs) are essential for many powered devices, and they are constantly being improved. One of the latest innovations is the use of 3D printers to create PCBs. However, even as new manufacturing methods are explored, some best practices for mitigating power supply noise remain unchanged.
First, PCB signal traces should be as short and thin as possible. Traces with a width of 4 to 8 mm and a thickness of less than 8 mm are generally ideal. Keeping PCB traces within the recommended limits should minimize capacitive coupling, thereby reducing noise, especially at high frequencies.
When planning trace layout, ensure that the distance between adjacent traces is always greater than their width. This reduces the likelihood of crosstalk. If there are two adjacent signal layers on the PCB, check if one layer has horizontal traces and the other has vertical traces; this is another way to reduce crosstalk. Using filters for power lines and all other PCB inputs can also mitigate noise.
When handling PCB traces related to sensitive signals, regardless of whether the traces and the oscillation circuit are located on the same PCB layer, they should be kept away from the oscillation circuit.
Designing PCBs with independent zones is another noise management technique that affects signal integrity. Separating analog and digital signals is best practice. Digital signals generate high-frequency noise, which can cause errors in both types of circuits. Similarly, high-frequency signals should be separated from low-frequency signals on the PCB.
Seeking regulatory options
Adding a second low-noise regulator at the power output is another consideration for noise reduction. This option increases the overall design cost, but it is a common practice.
Low-dropout linear regulators are commonly used to reduce power supply noise. This can reduce output ripple by at least an order of magnitude or more. Using LC or RC filters can further improve noise reduction.
However, if you choose to use RC or LC filters in your design, take the time to select the most suitable filter. RC filters require a well-ventilated power supply to effectively dissipate the heat generated by the resistance. Furthermore, while RC filters are relatively inexpensive, they are only suitable for small load currents and are best suited for managing low-power signals.
Conversely, LC filters are suitable for larger current loads and can mitigate high-power signals. These filters do not require additional ventilation because the inductors do not generate heat.
A realistic view on power supply noise
These strategies will help you control noise in your power supply. However, it's important to remember that you cannot eliminate noise, so it's always helpful to define acceptable noise levels for your product.
Once this is determined, selecting one or more of the strategies mentioned above and applying them to achieve the desired results becomes much easier. If you are designing an updated version of a previous product, incorporating customer feedback can highlight design flaws, thereby reducing power supply noise and bringing other benefits.
