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Resistive Components
Pulse Withstanding Chip Resistors
PWC Series
Today's electronic devices are becoming smaller and smaller. As a result designers are moving more towards surface mount components not only for new designs but also to design out large axial and other through-hole resistors. In most cases this is a straightforward task as several resistor manufacturers offer chip resistors with performances to match axial parts. However in some cases, due to power rating or pulse withstanding requirements, this has been impossible. The requirement, in particular, for pulse withstand capability is growing due to the need to protect sensitive modern electronic systems.
To meet this demand TT electronics have designed a Pulse Withstanding Chip Resistor (PWC Series). The PWC series is available in four standard sizes from 0805 to 2512 as shown in the following table. The table also gives details of the improved LEV (Limiting Element Voltage) and increased power rating. Pulse withstanding details are given on the following pages. The enhanced performance of the chips is made possible by the precise use of the best resistance inks and a closely controlled production process.
* Excellent pulse handling performance * Cost effective custom designs available * Field proven with millions of units in use * Standard and custom chip sizes (0805 to 2512)
Subsidiaries of TT electronics plc
Leading in Tomorrow's Technology
2
Size Power @70C Resistance range Tolerance LEV TCR Operating temperature Values Pulse capability
*0.5% Tolerance only available on values 10R to 1MO.
0805 0.125W
1206 0.33W 1R0 to 10M 0.5*, 1, 2, 5%
2010 0.75W
2512 1.5W
150V
200V
400V
500V
<10R:200ppm/C 10R:100ppm/C -55 to +155C E96 preferred other values to special order See following pages
Applications
Applications vary from line protection for telecommunications to surge withstanding resistors for use in circuit breakers. Details of a typical telecomm and power supply application are given below. Telephone lines can be subjected to a large range of voltage disturbances, many of which can damage switching equipment. This has led to the need for circuit protection against both high voltage transients, usually of short duration caused by lighting strikes and overloads of longer duration, due to direct connection to mains power lines. These two faults are separated into primary and secondary protection. Primary protection handles the high voltage transients, and is usually located within the exchange. Secondary protection is usually built into the equipment to be protected, and deals with both current and voltage limiting. Voltage limiting prevents damage to the equipment and shock hazards, and current limiting prevents damage to wiring. A typical application circuit is shown in fig 1 where the resistors are designed for ring signal sending through a solid state relay. The resistors are protected from lightning surge by Over-voltage Protection in the system and the resistors are required to withstand pulses of 15 Watts for 1 second and 75 Watts for 0.1 second, repeated 60 times. Test requirements for telecomms applications are laid down by the International Telecommunications Union (ITU) and Bell Communications Research (Bellcore). Fig 2 shows a typical power supply or battery charger circuit. In this application the resistor is required to withstand a small inrush surge, and also a lightning strike surge. The lightning strike is usually simulated by applying either a 1.2/50s or 10/700s pulse shape, the number of pulses and pulse intervals being specified by the customer or the relevant standard. Typical standards to be met are Cenelec EN50082-1 and EN50082-2 which are part of the European EMC directives, and Bellcore 1089 for the US market. To determine the suitability of a PWC series chip resistors for your application refer to the pulse withstanding data as given below. Graphs have been produced to show the PWC performance under single and continuous pulse, maximum pulse voltage for single and continuous pulses and lighting surge performance using both 1.2/50s and 10/700s pulse shapes.
Welwyn Resistor
Lightning Surge
Line
Over Voltage Protection
Input Power Supply Circuit Welwyn Resistor
Output
Fig 1
Fig 2
3
Description of Performance Tests Single Impulse
The single impulse graph was the result of 50 impulses of rectangular shape applied at one minute intervals. The limit of acceptance was a shift in resistance of less than 1% from the initial value. The power applied was subject to the restrictions of the maximum permissible impulse voltage graph as shown. The formula used to calculate the average power for repetitive pulses is shown below.
2 P = V ti R tp
For a rectangular impulse
< Pnom
Continuous Load Due to Repetitive Pulses
The continuous load graph was obtained by applying repetitive rectangular pulses where the pulse period (tp) was adjusted so that the average power dissipated in the resistor was equal to its rated power at 70C. Again the limit of acceptance was a shift in resistance of less than 1% from the initial value.
2 For an exponential impulse P = V te < Pnom R 2tp
Where
R = nominal resistance tp = time of the pulse period (1/tp = pulse frequency) V = peak voltage of the impulse P = average power dissipation of continuous pulses ti = impulse time of a rectangular pulse Te = time constant of an exponential pulse
Rectangular Pulses
Exponential Pulse
Resistive Components
Single Pulse
1000
4
Pulse Power P (W)
100 0805 1206 2010 2512 10
1 0.0001
0.001
0.01 Pulse Duration ti (s)
0.1
1
Continuous Pulses
100
Pulse Power P (W)
10 0805 1206 2010 2512 1
0.1 0.0001
0.001
0.01 Pulse Duration ti (s)
0.1
1
Pulse Voltage
10000
Pulse Voltage (Volts)
1000 O805 1206 2010 2512 100
10 0.0001
0.001
0.01 Pulse Duration ti (s)
0.1
1
Resistive Components
5
Lightning Surge
Resistors are tested in accordance with IEC61000-4-5 using both 1.2/50s and 10/700s pulse shapes and Bellcore 1089 using both 2/10s and 10/1000s pulse shapes (2512 size only). The limit of acceptance is a shift in resistance of less than 1% from the initial value.
1.2/50s Lightning Surge
10000
Peak voltage (volts)
1000 0805 1206 2010 2512 100
10 1 10 100 1000 10000 Value (ohms) 100000 1000000 10000000
10/700s Lightning Surge
10000
Peak Voltage (Volts)
1000 0805 1206 2010 2512 100
10 1 10 100 1000 10000 Value (ohms) 100000 1000000 10000000
PWC2512 Pulse Testing to Bellcore 1089 Specification
10000
1000 Volts Applied
10/1000s 2/10s
100
10 1 10 100 1000 10000 Value (ohms) 100000 1000000 10000000
6
Resistive Components
Performance Data
Maximum Load at rated power: Shelf life: Overload:
1000 hours at 70C
Typical 0.25 0.02 Zero at 155C 0.1 0.2 0.25 0.05 0.05 500
R% R% R% R% R% R% R% Volts
2 0.1 1 1 1 0.25 0.25
12 months at room temperature
Derating from rated power at 70C
6.25 x rated power for 5 seconds
Dry heat: 1000 hours at 155C Long term damp heat Temperature rapid change Resistance to solder heat Voltage proof
Note: An 0.01 ohm addition to be added to the performance of all resistors <10 ohms.
Physical Data
Dimensions of PWC chips are given below in mm and weight in g.
L 0805 1206 2010 2512 2.00.3 3.20.4 5.10.3 6.50.3 W 1.250.2 1.60.2 2.50.2 3.20.2 T max 0.6 0.7 0.8 0.8 A 0.30.15 0.40.2 0.60.3 0.60.3 B* 0.9 min 1.7 min 3.0 min 4.4 min C 0.30.1 0.40.15 N/A N/A Wt. 0.009 0.020 0.036 0.055
A B L A W T Wrap-around terminations (3 faces)
* This dimension determines the number of conductors which may pass under the surface mounted chip.
Construction & Solderability
Thick film resistor material, overglaze and organic protection are screen printed on a 96% alumina substrate. Wrap-around terminations have an electroplated nickel barrier and tin-lead solder coating, this ensures excellent `leach' resistance properties and solderability. Chips can withstand immersion in solder at 260C for 30 seconds.
TT electronics has over 60 years experience in designing and manufacturing resistive components.
Welwyn Components Limited
Welwyn Electronics Park, Bedlington Northumberland NE22 7AA, UK Telephone: +44 (0) 1670 822181 Facsimile: +44 (0) 1670 829465 Email: info@welwyn-tt.com Website: www.welwyn-tt.com
IRC Inc. (AFD)
4222 South Staples Street Corpus Christi, Texas 78411, USA Telephone: +1 361 992 7900 Facsimile: +1 361 992 3377 Email: ircafd@irctt.com Website: www.irctt.com
Leading in Tomorrow's Technology
General Note Welwyn Components / IRC reserves the right to make changes in product specification without notice or liability. All information is subject to Welwyn's / IRC's own data and is considered accurate at time of going to print. (c) Welwyn Components Limited
Subsidiaries of TT electronics plc Issue B * 01.03

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