Posted on 01 March 2019

Circuit Protection Designs for a Connected World

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Integrating overcurrent and overvoltage protection

The demand for more and more features and functions in consumer electronics presents new challenges to design engineers. Circuit protection device manufacturers must also continue to deliver new solutions to support emerging technologies and meet new system level protection requirements.

By Adrian Mikolajczak, Tyco Raychem Circuitprotection


The electronics industry’s unrelenting demand for smaller, more reliable circuit protection devices continues to drive the miniaturization trend. As a result, circuit protection device manufacturers must provide their OEM customers with smaller and smaller devices; but the objective is clearly more than size reduction. The real challenge lies in scaling down component size without sacrificing electrical characteristics. Advanced material research and technology has been the key to developing new devices that meet existing performance levels within smaller, more reliable, and more convenient packaging.

Another important design challenge is the need for coordinated circuit protection. Because overcurrent and overvoltage protection are often viewed as two unrelated elements of the design process, protection strategies can result in costly multi-component solutions, and synergies between protective devices can be overlooked. Coordinating these devices or integrating overcurrent and overvoltage protection functions in a single device effectively reduces component count and, appropriately applied, can expand performance attributes and help improve system reliability.

2Pro™ Device helps protect telephony and VoIP equipment

Following are three examples of how Tyco Electronics’ applied innovation in circuit protection materials and technology can help design engineers conserve valuable board space and meet evolving safety and performance standards.

The new 2Pro™ device integrates overcurrent and overvoltage circuit protection technology to help prevent damage to telephony communications equipment. The device’s small footprint, resettable functionality and coordinated protection capabilities make it suitable for a wide range of telephony and VoIP equipment applications such as cordless phones, VoIP gateways, data modems, set-top boxes, security systems, MDF (Main Distribution Frame) modules, analog linecards and ISDN (Integrated Services Digital Network) linecards.

The RoHS-compliant 2Pro device incorporates PolySwitch™ PPTC overcurrent technology with an MOV component into one thermally protected device that helps provide current limiting during overcurrent events and voltage clamping during overvoltage events. This singledevice approach helps reduce component count and improve equipment reliability. Figures 2 and 3 illustrate how the 2Pro device is used in both an ungrounded and grounded circuit protection scheme.

2Pro in ungrounded (2) and in grounded system (3)

The 2Pro device helps equipment manufacturers comply with UL 60950 and remain operational after specified lightning tests. It also helps equipment comply with surge tests per TIA-968-A, IEC 60950, and ITU-T K.20/K.21. The UL 497A listed protector also helps provide ESD protection, improve network reliability, reduce maintenance and warranty costs, and enhance user-satisfaction with Customer Premise Equipment.

PolyZen™ Device helps protect against charger-induced system failure

The continuing miniaturization trend in portable and desktop electronics necessitates the use of external power supplies for normal operation and/or charging. However, the widespread market availability of external and universal power supplies forces the design engineer to incorporate additional safeguards against unexpected damage caused by use of unauthorized charging systems, a leading cause of device warranty returns. Complicating the challenge, the solution itself must be designed to accommodate ever-smaller portable electronic packages. Tyco Electronics recently introduced the PolyZen™ device to help provide DC power port protection for portable electronics and systems using barrel jacks for power input. The PolyZen device is a polymer-enhanced, precision Zener diode micro-assembly. It consists of a low resistance, precision Zener diode that is thermally coupled to a PPTC “thermal switch.”

PESD devices help protect high-speed ports on set-top boxes and portable devices

In operation, extended overvoltage or reverse bias conditions will cause the PPTC element to “trip” as the diode begins to heat up. A “trip event” causes the PPTC “thermal switch” to transition from a low to high-resistance state, helping protect downstream electronics by generating a series element voltage drop. Also, by limiting the current, it helps to prevent Zener diode failure caused by thermal runaway.

Simply put, the PolyZen device helps provide coordinated protection with a component that protects like a Zener diode, but is capable of withstanding very high power fault conditions without requiring any special heat sinking structures beyond normal PCB traces. The PolyZen solution helps protect sensitive electronics from damage caused by inductive voltage spikes, voltage transients, incorrect power supplies and reverse bias. These devices offer power handling on the order of 100 watts (depending on device) in a 4mm package, have the ability to withstand high current inrush and faults in a small form factor, and are particularly suitable for portable electronics and other low-power DC devices. At the high-speed data rates of USB 2.0, IEEE1394, DVI and HDMI, the parasitic impedance of traditional protection devices can distort and deteriorate signal integrity. Low capacitance ESD protection is critical to maintaining data integrity at these high speeds.

Figure 6 shows a typical HDMI circuit protection design utilizing Raychem Circuit Protection's PESD device. These protection devices shunt ESD away from sensitive circuitry and provide exceptionally low capacitance compared to traditional MLV (multilayer varistor) or TVS (transient voltage suppression) diode technology.

Typical HDMI circuit schematic with PESD devices (based on HDMI Specification Version 1.2)

They perform better than other comparable components in transmission line pulse (TLP) testing, as well as IEC62019-4-2 testing, especially after multiple hits (up to 1000). The PESD's low trigger voltage and low clamping voltage also helps protect sensitive electronic components.

Integrating polymeric materials into "traditional" products such as MOVs and Zener diodes has expanded PPTC technology to a wider range of industries and applications - from automotive navigation systems to USB ports, from security and fire alarm systems to cell phones and set top boxes. Pioneering designs - based on Tyco Electronics' commitment to anticipating market trends and collaborative relationships with electronic OEMs - have helped the company deliver new and innovative products to support emerging technologies, reduce warranty repair costs, and meet new safety and performance requirements.



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