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Utech Electronics - Press Release

Stackpole Product Highlight - Pulse Handling Resistors

   

This product highlight will discuss applications which experience an electrical overload stress and the design challenges in dealing with that. It will address both high voltage and higher power / current pulses and discuss the various solutions that Stackpole offers for each of these unique situations. The intent is to provide a basis for talking to engineers about their requirements and knowing the key information needed and the important questions to ask.

Pulse Power Requirements

Pulse power and current requirements often stem from power electronics turning on or off, or from electric motor start / stop. The pulses are generally much longer in duration than the usual high voltage pulses and as a result, a robust resistive element technology, little or no calibration trimming, and more resistive element mass are desirable.

For axial leaded film and composition resistors in power ratings of 5W or less, the best choices would be the RC series of Carbon Composition resistors, the RSF/RSMF series of metal oxide resistors, and the RSPF / RSPL series of flameproof power resistors. Carbon Comps are known for their outstanding pulse handling capability and extremely low inductance. The disadvantage of comps is their limited resistance tolerance, poor environmental performance and cost. Metal Oxides provide the lowest cost solution and are the most readily available. The RSPF / RSPL series has a more robust resistive element designed for higher power surges than metal oxides. However, the pulse handling of the RSF / RSMF and RSPF / RSPL is limited due to the relatively small resistive element mass.

Wirewound resistors such as Stackpole's WW and CB series provide an even greater level of pulse power performance. Because the mass of the wire used for these is significantly more than either of the film elements above, wirewounds will typically provide 5X to 10X the pulse handling of the equivalent size film resistor. Compared to carbon comps, wirewounds offer a much more stable and precise resistor performance with outstanding reliability in all types of environments. In addition, wirewounds have a great deal of flexibility in their design and construction, allowing Stackpole to create a specific resistor with the desired characteristics for a particular customer or application. From a pricing standpoint, wirewound resistors will be a bit more expensive than an equivalent film resistor, so there is a price to be paid for the superior electrical performance. The inherent inductance of a wirewound, even those that are non-inductively wound, mean that wirewounds are not a good choice for high speed switching power supplies; carbon comps are still the most popular choice for in that case.

Stackpole

For SMD resistors the RPC is the surge withstanding thick film chip series designed for high pulse power and current applications. The RPC uses of the entire width of the ceramic for the resistive element because the laser calibration trim is either limited or eliminated. This allows the RPC to handle pulses that are from 2X to more than 10X higher in magnitude than a standard thick film chip. The relatively low price of the RPC compared to other surge resistor solutions makes it the most popular choice for many types of applications where the device will only see a pulse infrequently or at low duty cycle. The smaller mass of the RPC resistive element prevents its use for extremely high pulse power handling or for applications with high pulse repetition rates. For those applications the SM series of surface mount wirewound resistors can be a better choice provided the switching speeds are reasonable. Like the wirewounds discussed previously, the SM product has enough elemental mass to take significantly higher pulsed power and provides the ability to run at higher temperatures. For pulse applications with more demanding requirements causing increased self heating, this higher temperature capability is critical in maintaining the integrity of the resistor and minimizing the resistance shift due to overload. The SM series also offers the same design and construction flexibility to enable Stackpole to design custom solutions to fit a particular application or customer requirement. In many cases, a custom wirewound can replace solutions using several other resistor types to reduce board space usage and cost.

Stackpole

High Voltage Pulses

High voltage pulses are typically very short in duration. Many times the need for a high pulse voltage resistor is driven by an industry standard requirement for ESD, power line cross, or lightning withstanding. For these requirements, a resistive element as long and narrow as possible is best. Lengthening the resistive element lowers the effective voltage stress per unit length. This concept is the basis for Stackpole's film-type high voltage pulse solutions.

Stackpole

For axial leaded resistors, the ASR / ASRM series is a power film type resistor designed specifically for high voltage pulse applications. For high voltage pulses and even repetitive pulse conditions, the ASR / ASRM is very competitive vs. other technologies. This series also has good pulse power handling as well making it a good all-around pulse resistor solution. For applications with lower TCR requirements or where moisture withstanding is critical, a metal glaze element such as in Stackpole's MG / MGM series is desirable. This series is also offered in a 3W power rating where the ASR / ASRM offers up to a 2W rating. However the pulse handling for the MG / MGM isn't as good as the ASR / ASRM, the resistance value range is limited, and it is more expensive.

For surface mount high voltage resistor requirements, Stackpole offers two different products. The RVC series is a lower cost solution for medium voltage applications while the HVC series offers very high working voltage capability per chip size. The RVC utilizes a screen printed serpentine resistor element that offers voltage ratings of 2 to 3 times better than the equivalent standard thick film chips. The HVC uses a proprietary deposition method for the resistive element, which allows for finer lines, more uniform resistive traces, and the highest voltage ratings with the highest resistance values. The HVC is capable of tolerances down to 0.1% and 25 ppm, which is the type of precision rarely seen using thick film technology. The price for the HVC is significantly higher than the RVC.

Stackpole

Applications

High pulse voltage and pulse power applications are can be found in virtually every market. Examples would be all types of power supplies (especially at the inputs and outputs), motor controls, welding equipment, plasma cutters, aerospace, medical applications, heart defibrillators, instrumentation, measurement, electricity metering and control, power factor monitoring and correction, UPS systems, LED lighting, industrial automation, and refrigerator and HVAC controls.

More Information and Data Sheets Available

For more information about Stackpole products, contact Stackpole Electronics, Inc. at

Stackpole Electronics, Inc.
2700 Wycliff Road Suite 410,
Raleigh NC 27607
phone: 919-850-9500
email: marketing@seielect.com
web: www.seielect.com.

Stackpole Electronics Inc. is a leading global manufacturer of resistors supplying to the worlds largest OEMs, contract manufacturers and distributors. Headquartered in Raleigh, N.C., the privately held company began manufacturing in 1928 as part of Stackpole Carbon Company in St. Mary's, Pennsylvania. Now part of the Akahane Stackpole Manufacturing Group (ASMG), Stackpole has manufacturing facilities in Japan, Taiwan, China and Mexico; warehousing facilities in El Paso, Shenzhen and Japan; and international sales offices in Tokyo, Taipei, London, Hong Kong and Shenzhen.

 



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