PCB Surge Protection: Designing Your PCB for Transient Voltage Suppression

Electronic systems in industrial environments, in aircraft, in power distribution, and in many consumer products can be at risk of experiencing power surges. When a surge occurs, a large spike of current propagates into the board through a power connection or other connector, causing damage to components and potentially causing system failure. A related even is electrostatic discharge (ESD), which essentially creates the same effect but with a different root cause.

To address these dangers in typical operational scenarios, multiple industry standards that define safety and transient withstand requirements have been developed. Surge protection and ESD protection are also an important part of passing EMC testing. There are three levels at which transient voltage suppression resulting from power surges can be addressed:

• In the enclosure design
• On the PCB with the right grounding strategy
• With components that divert or absorb transient voltages

In this guide, we’ve included multiple resources that outline component selection, placement, and grounding practices to ensure maximum ESD protection in a PCBA. These three areas can be addressed with the layout tools and component selection features found in Altium Designer, the industry’s best software for PCB design.

PCB Surge Protection Strategies

If you use power strips for your home electronics, then you’re already aware of the surge protection they provide. In the event of a lightning strike, power surge on the mains line, a short in your home electrical wiring, a surge protector will act as a voltage suppressor and dampen the transient received at the power input. Surge protection focuses on either diverting, absorbing, or completely blocking transient currents of different edge rates and peak voltages.

Selecting Transient Voltage Suppression Components

Transient voltages arise in electronics in two ways: as power surges on power bus lines, and from ESD events that inject a pulse into power or data lines. As such, some components can protect against both ESD and surges. There are two important specifications for selecting these components:

• Response time
• Withstand voltage, current, and/or power rating

There are multiple options for transient voltage suppression components and surge protection. These components provide surge protection over different ranges and transient edge rates, and they can be combined in a cascaded configuration to provide maximum protection for electronic devices.

The protection level provided by these components varies widely, so they have been roughly categorized into protection ranges as shown in the above table. The table also lists how these are connected in circuits; an example with bidirectional TVS diodes is shown below.

Placement of Surge Protection Devices

Ideal placement of surge protection components is near the location where a PCB could be exposed to a transient event. Surge protection components should interact with the incoming ESD pulse before the pulse has a chance to damage any other components. Typical areas where ESD exposure could occur include connector surfaces, exposed pins, power/barrel connectors, buttons, and switches. An example placement is shown below.

• Learn more about placement of surge protectors are shunt elements

The same idea applies to surge protection devices like circuit breakers, resettable fuses, relays, and gas discharge tubes. For example, these components are often used on main power inputs, so they should be placed on the PCB near that connector.

On the PCB, it is preferable to place TVS diodes, gas discharge tubes, or metal oxide varistor as a shunt element across the protected line. This applies for signal and power lines. The PCB layout image below shows placement of three TVS diodes; two are on a differential pair and one is on a power bus line coming from a USB-A connector.

The schematic shown above illustrates a connection between the chassis GND and the system GND, the latter of which is used to reference signals in the data lines. This connection is important for ESD protection but it should generally not be placed at the connector. Instead, the placement of this connection is an important part of a grounding strategy that designers must consider if a chassis ground is present in the system.

Grounding

While surge protection devices that absorb and/or bypass transients are important for device protection, the best strategy for surge and ESD protection begins with the right grounding strategy. Ground regions in a design can act as a safe conductor for dissipating currents from ESD events. A PCB layout that is expected to receive strong transients or that connects to line voltages should have the right grounding strategy to protect against ESD and faults.

• Learn more about types of grounds in a PCB layout

A connection back to the chassis ground and eventually earth ground (assuming these are present) can be made on the board. This provides excellent ESD protection, especially on metalized cable housings and shielded cables. With surge protection, a shunt element can divert a transient through a direct connection back to the chassis or system ground. It’s important to determine where power surges will be dissipated when designing your system and determining your PCB layout topology.

Which Systems Need Surge Protection?

Not all PCBs will be part of a system that will be exposed to high voltages or ESD events. There are EMC standards that apply to general-purpose electronics; these are specified by FCC/CE in the US and Europe, but there are others suited for different countries. Other industry groups and government agencies have specified certain ESD requirements for electronics in different industries or application environments, such as:

• MIL‑STD‑1686
• ANSI standards
• ISO standards
• IEC standards
• DO-160 standards
• SAE J-tests
• FAA standards

These groups of standards cover systems from commercial office equipment to military, automotive, aircraft, and medical devices. Specialized testing facilities will offer compliance verification services against these groups of standards. These standards are part of broader EMC testing and compliance, make sure you understand the best strategies for implementing ESD protection.

• Learn more about EMC compliance

No matter which PCB surge protection components you choose for your PCB, you’ll need to work with design software that makes it easy to find, place, and route these components. Whenever you need to find PCB surge protection components for your board, use the CAD tools in Altium Designer^®. When you’ve finished your design, and you want to release files to your manufacturer, the Altium 365^™ platform makes it easy to collaborate and share your projects.

We have only scratched the surface of what’s possible with Altium Designer on Altium 365. Start your free trial of Altium Designer + Altium 365 today.