AN580/0393 application note (example of the 10/700 m s surge) voltage to current waveform conversion ? a. bremond generator diagram open output surge waveform figure 1 : ccitt 10/700 m s surge definition introduction ccitt members have generated a great deal of recommendations which have permitted national administrations to publish local standards. in particular they have defined a 10/700 m s surge waveform and its associated generator diagram (see fig.1). it is important to note that the given waveform is the generator output voltage without load. for a protection component user the most important parameter to take into account is the current waveform flowing through the surge suppressor. the goal of this paper is to give the current waveform parameters. t2 t'1 t1 1 0.9 0.5 0.3 0 t1 = 1.67 t'1 = 10 s t2 = 700 s t v r2 15 r3 25 r1 50 c1 20 f c2 0.2 f 1/4
2 - waveform calculation 2.1 : generator output voltage without load. figure 2 : voltage rise time the equation of this curve is : v(t) = vp (1 - exp (- t/t)) ? t = - t log n (1 - (v(t)/vp)) (1) in this case the time constant may be estimated as : t=r 2 c 2 so t(0.3) and t(0.9) will be calculated respectively with v(t)/vp = 0.3 and 0.9 t(0.3) = 1 m s t(0.9) = 6.9 m s and then t1 = 1.67 (t (0.9) -t (0.1) ) = 9.8 m s 10 m s figure 3 : voltage duration 03ab0504 t v 1 t2 (vp) 0.5 the equation of this curve is: v(t) = vp exp (- t/t)) ? t = - log n (v(t)/vp)) (2) with a time constant due essentially to r 1 and c 1 t=r 1 c 1 so t 2 may be calculated with v(t)/vp = 0.5 ? t2 = 693 m s 700 m s 02ab0504 t v 1 0.9 0.3 t1 t'1 t'1 = t(0.9) - t(0.3) t1 = 1.67 t'1 (vp) 2.1.1 : rise time 2.1.2 : voltage surge duration ? application note 2/4
figure 4 : ccitt 10/700 ms generator with output in short circuit figure 5 : current rise time c1 r2 r3 r1 c2 04ab0504 i 05ab0504 t i 1 0.9 0.3 t1 t'1 t'1 = t(0.9) - t(0.3) t1 = 1.67 t'1 (ip) 2.2.1 : rise time in this chapter we will do the calculations with the generator output in short circuit (see fig.4), this is generally the case during the surge suppressor action (for example the trisil technogy devices from sgs thomson). 2.2 generator short circuted output current. the formula (1) given in the chapter 2.1.1. remains true, but the time constant must take into account r 3 and may be estimated as : t=(r 2 r 3 /(r 2 +r 3 )) c 2 so t (0.3) = 0.67 m s t (0.9) = 4.3 m s ? t1 = 1.67 (t(0.9) - t(0.1)) =6 m s 5 m s figure 6 : current duration 06ab0504 t i 1 t2 (ip) 0.5 2.1.2 : current surge duration. the formula (2) given in the chapter 2.1.2. remains true but the time constant is now due to the capacitor c 1 with the resistor r 1 in parallel with r 2 +r 3 t=(r 1 (r 2 +r 3 )/(r 1 +r 2 +r 3 )c 1 ? t2 = 308 m s 310 m s ? application note 3/4
3-summary the 10/700 m s surge waveform given by the ccitt recommendation is a voltage wave produced by the generator in open circuit. this curve is very important as a test reference for telecommunication equipment. the protection function designers or users have to know the actual current waveform flowing through the protector in order to optimize it. the 10/700 m s ccitt generator gives a 5/310 m s current wave when its outputs are in short circuit. (in the case of a crowbar device, for example trisil). for certain cases the resistor r3 is equal to zero and then the duration time becomes 160 m s. please note that in certain documents we find a 8/320 m s current wave which represents the same surge test. information furnished is believed to be accurate and reliable. however, sgs-thomson microelectronics assumes no responsability for the consequences of use of such information nor for any infringement of patents or other rights of third parties which may result from its use. no license is granted by implication or otherwise under any patent or patent rights of sgs-thomson microelectronics. specifications mentioned in this publication are subject to change without notice. this publication supersedes and replaces all information previously supplied. sgs-thomson microelectronics products are not authorized for use as critical components in life support devices or systems without express written approval of sgs-thomson microelectronics. ? 1995 sgs-thomson microelectronics - printed in italy - all rights reserved. sgs-thomson microelectronics group of companies australia - brazil - france - germany - hong kong - italy - japan - korea - malaysia - malta - morocco - the netherlands - singapore - spain - sweden - switzerland - taiwan - thailand - united kingdom - u.s.a. ? application note 4/4
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