Optimized High-Power Bus Protection with Less Soldering

High-density direct-current (DC) bus power protection using through-hole designs typically requires two soldering operations during the manufacturing process. Discrete flat no-leads (DFN)-package TVS (transient voltage suppression) diodes from Bourns Inc. utilize a surface-mount design, eliminating bottom-side soldering operations for modern designs with high-power protection components.

When looking to provide power protection to a system, a thorough examination is conducted to determine what potential threats to the circuit components exist. In the case of Power TVS (PTVS) components or voltage clamping devices, the diode is rated by the length of time the surge voltage occurs and the maximum current from independent power producers (IPPs) it can handle. Reducing the amplitude of the voltage while conducting current is crucial until the surge time finally ends.

Protection from excessive voltage—which can result from power line transients, motor arcing, lightning strikes, and electrostatic discharge (ESD)—eliminates the need to repair and replace damaged vital components.

As a global leader in circuit protection, Bourns provides a broad line of overvoltage and overcurrent protection components, including low capacitance protection.

Always on guard, always protecting vital components

When they are performing perfectly, power protection components go unnoticed until a fault reaffirms their necessity. However, protection must be adequate, or the system remains vulnerable, and the potential for serious damage exists. This can become costly when there is downtime or a need for maintenance calls.

Telecoms that use AC and DC power supply systems always require protection from such events as indirect lightning strikes and power line surges.

Bourns’ DFN-packaged PTVS devices offer many features that provide both effective and optimal protection for a variety of signal-level and power circuits.

The PTVS2-058C-H is a surface-mount, general-purpose PTVS series diode that is ROHS3 compliant (Figure 1). With a 2-kA, 8/20-µs surge capability, it offers repetitive standoff voltage of 22 to 86 V and bidirectional TVS. High-power DC bus protection and resilience against lightning strikes and inductive and transient surges up to rated limits put the PTVS2-058C-H among the best of high-current TVS diodes.

Figure 1: The PTVS2-058C-H PTVS series diode offers excellent performance over a range of temperatures. (Image source: Bourns)

Defining the terms for the task

Specific terminology becomes evident when researching TVS diodes—learning the basics can make a search much easier to find the right protection components:

• Peak pulse current (IPP): The maximum surge current a diode can handle without damage.
• Clamping voltage (VC): The maximum voltage across the protection circuit for a given IPP.
• Repetitive reverse standoff voltage (VWM): This is the normal operating voltage threshold, also known as the maximum working peak voltage. The applied voltage across the diode is less than the threshold due to the circuit protection provided by the high-impedance TVS diode.
• Breakdown voltage (VBR): This is the threshold at which the TVS diode starts to conduct a specified current and should not exceed the maximum for the protected integrated circuit.

Many levels of protection are needed

When it comes to troubleshooting potential faults, there are always going to be options.

Typically, a circuit requires many types and levels of protection. In addition, for circuits needing two or more levels of input-voltage transient protection, the coordination of component capabilities provides a heightened level of defense so that components can achieve optimal performance.

PTVS diodes, as a clamping component, prevent voltage exceeding preset levels by suppressing startup and inductive transient voltages, with the clamp function releasing once the overvoltage clears. A TVS clamp is a silicon bipolar junction. It’s similar to a Zener diode but able to survive reverse breakdown voltage, dissipating a relatively short transient event.

The clamping TVS differs from a crowbar component, which holds the voltage at a low value across itself until the surge passes.

Along with silicon, clamps can be constructed utilizing a metal oxide varistor (MOV), a bidirectional semiconductor voltage transient suppressor. Typically, the voltage across the device decreases as the current through it increases. Compared to a PTVS diode, the MOV causes the voltage to lower and remain constant as the current continues to increase after an initial short-duration peak. In addition, a PTVS diode has a much lower clamping voltage than an MOV for the same surge current.

The surface-mounted ESD9B5.0ST5G diode (Figure 2) is part of the ESD9B series, designed to protect sensitive components from electrostatic discharges (ESD), with low leakage, fast response times, and excellent clamping capability. Its small size makes it well-suited for mobile phones, MP3 players, and myriad portable applications where board space is at a premium.

Figure 2: With small body outline dimensions of 1.0 mm by 0.60 mm and a low body height of 0.4 mm, the onsemi ESD9B5.0ST5G is ideal for today’s miniaturized components. (Image source: Bourns)

How to choose the right diode

Most PTVS diode suppliers include generic selection guidelines in their data sheets. When choosing a diode, the characteristics of the circuit that needs electrical protection and the circuit's test standard usually come to the forefront. The standard cited most frequently is IEC 61000-4-5.

When selecting a PTVS diode, consider one with a standoff voltage higher than the application’s expected operating voltage. Find the absolute maximum voltage rating of all devices along the protected line and select a diode with a maximum clamping voltage lower than that.

Underrated diodes or those not designed for the maximum current will likely fail in a surge event, destroying the circuit. “Expect the worst” is one adage to remember, so verifying that the specified peak current IPP will safely exceed the expected peak current in every situation goes a long way toward avoiding potential failures and damage to valuable circuits.

PTVS diodes and port protection

PTVS diodes are also ideal for protecting power ports, both outputs from power supplies and power inputs, especially when a long distance separates the two functions.

In the case of exposure to surge events in remote operations for power connection wires, Power over Ethernet (PoE), power-sourcing equipment (PSE), and power delivery (PD), the connections at the RJ-45 port connectors must be protected. To ensure this, devices are available to protect the maximum telecom and PoE supply voltages of 60 V, including 48 V surge protection in 5G small cells.

Bourns provides surface-mount DFN packages for exactly these needs with diodes such as the PTVS1-026C-H for 1 kA and PTVS2-026C-H for 2 kA, effective for 24 V telemetry systems and industrial control.

Conclusion

Transient power, motor arcing, electrostatic discharge, and lightning strikes all pose a real threat to damaging vital electrical circuits. Utilizing the right layers of protection through surge-protective diodes, like those offered by Bourns, Inc., is vital to avoid costly repair and replacement—not to mention production and service downtime.

Bourns has established itself as a global leader in circuit protection, providing a broad line of overvoltage and overcurrent protection components and low capacitance protection.