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www.ttiinc.com Solutions Guide CIRCUIT PROTECTION A Berkshire Hathaway Company

www.ttiinc.com Solutions Guide CIRCUIT PROTECTION A Berkshire Hathaway Company The Specialist in Electronic Component Distribution Why Buy from TTI? Founded in 1971, TTI has steadily grown to become the world’s leading interconnect, passive, electromechanical and discrete component distributor in the industry. The company was founded on the premise that passive component purchasing could be made more efficient by offering product specialization, customer-driven service and proprietary supply chain solutions. Product Experts Our unique specialization enables us to provide significantly better product knowledge to support manufacturing from design through production. TTI’s commitment to this specialty and our customers is as dedicated today as always. Broader and Deeper Inventories TTI maintains extensive inventories, stocking more than 500,000 part numbers in North America and over 850,000 globally – that’s more interconnect, passive, electromechanical and discrete inventory available than from any one other source. Advanced Inventory Management (AIM) Platform TTI’s proprietary system is specifically designed for managing IP&E products and partnerships with premier manufacturers. This allows us to provide the BOM coverage necessary to deploy comprehensive supply chain solutions that reduce total cost of ownership and mitigate line down risk. Quality and Reliability TTI was the first distributor to have all global warehouse locations ISO registered and currently are rated ISO 9001:2008 and AS9100C in North America, ISO 9001:2008, EN 9100C and EN 9120:2009 in TTI Europe and ISO 9001:2008 in TTI Asia. Year after year, customers rate our inventory availability, on-time delivery and accuracy among the very best in the industry – call 1.800.CALL.TTI or visit us at www.ttiinc.com and discover why. Fort Worth, Texas TTI, Inc. Global Headquarters Circuit Protection Solutions Guide 2 Table of Contents What is Circuit Protection? .......................................................................................................................... Common Circuit Protection Threats ........................................................................................................ Electrostatic Discharge (ESD) ................................................................................................................. ........................................................................................................................................................... ................................................................................................................................................ .................................................................................................................................................... Applications ....................................................................................................................................................... ....................................................................................................................................................... .................................................................................................................................................. .......................................................................................................................................................... ............................................................................................................................................... ................................................................................................................................. ........................................................................................................................................... ............................................................................................................................................................. 4 6 8 10 12 14 16 18 20 22 24 26 28 30 www.ttiinc.com • 1.800.CALL.TTI 3 Circuit protection is an insurance policy. Most customers buy circuit protection never planning to use it, but it is critical to protect circuits from unexpected, damaging surges of current and voltage. Two types of circuit protection are available: overcurrent and overvoltage. What is Overcurrent Protection? An overcurrent condition is caused by excessive current (more than the maximum amount of current a product is designed to withstand under normal conditions) passing through a circuit. Overcurrent conditions have the potential to cause severe damage to a circuit, possibly leading to fire. Overcurrent protection is placing a component, usually a standard fuse or a Polymer Positive Temperature Coefficient (PPTC) resettable fuse or a Positive Temperature Coefficient (PTC) thermistor, in series with the device being protected. Standard fuses interrupt the current flow and PPTC resettable fuses and PTC thermistors limit the current to an acceptable level during overcurrent conditions, thus preventing catastrophic events. When no overcurrent condition exists, these products lie dormant within the circuit with a minimal amount of resistance to the circuit. What Technologies are Available to Provide Overcurrent Protection? TTI carries three technologies classified as overcurrent devices to provide protection to customers: fuses, PPTC resettable fuses and PTC thermistors. How Overcurrent Protection Products Operate? Standard Fuses: Fuses are an intentionally weak link in a circuit. A standard, one-time fuse with the correct rating will open or “blow” before the circuit reaches a damaging level or fire hazard. The event of the opening breaks the circuit and prevents current from flowing past that point. A standard fuse will open once and then must be replaced. Resettable Fuses: A resettable fuse does not open like a standard fuse. Rather it creates a very high resistance that prevents most of the current from flowing past it into the device on the circuit being protected. The resettable fuse then “resets,” as the name implies, once the overcurrent condition subsides. PTC Thermistor: Similar in function to a resettable fuse, a PTC thermistor creates a very high resistance to the current at a particular temperature caused by additional current. This temperature (called “switching temperature”) shelters the device from overheat or overcurrent. Once the overheat or overcurrent event is removed, the thermistor will cool down and reset, just like a resettable fuse. Why is Overcurrent Protection Important? There are three main reasons why overcurrent protection is needed in a circuit: safety, reliability and compliance. Safety: Using circuit protection helps guarantee safety as it protects from catastrophic events such as large surges of current that could cause fires. Reliability: Using overcurrent protection provides the reliability that components will be protected in the event that an overcurrent condition occurs. It also provides assurances that when the condition is cleared; the product will continue to function. Compliance: Many agencies (e.g. UL, CSA, VDE, etc.) now require circuit protection in electronic devices. Where is Overcurrent Protection Needed? All circuits and applications need overcurrent protection. What is Circuit Protection? Circuit Protection Solutions Guide 4 What is Overvoltage Protection? Like overcurrent protection, overvoltage protection is the safeguarding of products from overvoltage conditions. Overvoltage conditions are often called “transients,” and are defined as short duration spikes in voltage resulting from a sudden release of previously stored energy. overvoltage conditions can be short or prolonged. Most applications will require both overvoltage and overcurrent protection for the circuit. What Causes an Overvoltage Condition? An overvoltage condition is caused by a variety of factors, including but not limited to: transformers converting energy from one voltage to another, lightning, electrostatic discharge (ESD), motor start-ups, and automotive load dumps. Why is Overvoltage Protection Important? There are many factors that require overvoltage protection. They include, but are not limited to the following: • 75% of field equipment failure is caused by Electrical Overstress (EOS) • With increasing speeds, semiconductor devices are becoming increasingly sensitive to voltage transients • Lightning strikes even several miles away can induce transient voltages into equipment • ESD events at 8kV or higher can be damaging to ICs that are internally protected to 2kV What Overvoltage Protection Devices are Offered by TTI? TTI offers several options to limit excessive voltage experienced in today’s circuits. These are: metal-oxide varistors (MOV), multi-layer varistors (MLV), protection thyristors, TVS diodes, diode arrays, gas discharge tubes (GDT) and polymer suppression devices. How do Overvoltage Protection Devices Work? These devices can either clamp or crowbar the undesired voltage to protect the circuit. Clamping devices are devices placed parallel to components being protected. When an overvoltage condition arises, the device goes from an extremely high impedance to one of almost zero, permitting the transient to follow the path of least resistance through the clamping device. The device then clamps at a voltage above the standard operating voltage, but below the level that would damage the device being protected. This additional voltage is dissipated by absorbing part and shunting the rest to ground. TTI offers clamping devices that include MOVs, MLVs, TVS diodes, diode arrays and polymer suppression devices. Crowbar devices are placed parallel to components being protected and change from very high impedance to very low impedance during an overvoltage event, but energy is dissipated differently. During an overvoltage condition, these devices operate like a switch, turning on to a low voltage state that is well below the normal operating voltage of the circuit. All energy is then shunted straight to ground and dissipated. TTI offers two crowbar devices, GDTs and protection thyristors. CIRCUIT PROTECTION COMPONENTS AVAILABLE FROM TTI Overcurrent Overvoltage Supplier Resettable Fuse Standard Fuse Thermistors Varistors Thyristors GDT TVS Diodes Diode Arrays ESD Suppression Polymer Suppression AVX ◆ ◆ ◆ ◆ Bourns ◆ ◆ ◆ ◆ ◆ ◆ ◆ ◆ Eaton Bussmann ◆ ◆ ◆ ◆ ◆ KOA ◆ ◆ ◆ Littelfuse ◆ ◆ ◆ ◆ ◆ ◆ ◆ ◆ ◆ Murata ◆ ◆ ◆ Panasonic ◆ ◆ ◆ ◆ TDK EPCOS ◆ ◆ ◆ TE Connectivity / Raychem ◆ ◆ ◆ ◆ ◆ ◆ Vishay ◆ ◆ ◆ ◆ ◆ ◆ www.ttiinc.com • 1.800.CALL.TTI 5 Common Circuit Protection Threats Circuit Protection Threat Solution Matrix Overcurrent Product Safety Ground Faults Occur when electricity travels to ground outside the design’s intended pathway. Current Transients Occur momentarily in response to a change in the equilibrium of a circuit and frequently when power is applied to, or removed from, a circuit. Circuit Overload Occurs when an electric circuit is carrying more current than it's designed to handle, potentially creating a fire hazard due to overheating. Circuit Threats Overcurrent and Ground Faults Lightning Electrostatic Discharge (ESD) Electrical Fast Transients (EFT) Inductive Load Switching Datacom Voltage Transients Current Switching Applications Grounded circuits and circuits near AC power lines Any circuit connected to the outside environment Circuits with human interfaces Circuits with inductive loads Motors, pumps, compressors, relays & AC distribution Ethernet, DSL, data bus, telecom Various electronic and electrical circuits Protection Needs Current interrupting and voltage capability Quick responsiveness, switching, and surge capabilities Quick response with high peak voltage rating Repetitive fast rise time and recovery High energy rating Quick response, low parasitic capacitance Proper blocking voltage and current carrying capacity Protection Components Fuses, Resettable Fuses, Thermistors Protection Thyristors, Varistors, uploads/Geographie/ circuit-protection-guide.pdf