accessories filter & ring core chokes fp, l and lp series rev. sep 29, 2003 page 1 of 5 description these filters and chokes are designed to reduce input in- terference and/or output ripple voltages occurring in appli- cations with switched mode power supplies. since all our filters contain a moly permalloy powder (mpp) ring core they feature very low dc losses as well as high dc mag- netisation and operate perfectly at the input and/or output of switching regulators ensuring effective filtering even at elevated dc current levels. these special characteristics allow the chokes to be operated at dc currents which con- siderably exceed the rated current, by accepting a corre- sponding gradual loss of inductance (unlike ferrite core chokes where inductance rapidly decreases above a cer- tain dc magnetising level). in applications where switching regulators have long supply lines, filters and chokes are used in order to prevent oscilla- tions caused by their negative input impedance. for further information refer also to switching regulator data for "option l", and to section: technical information: installation & ap- plication . table 1a: type survey of fp filter blocks filter type matching switching part no. regulator type fp38 psr 54 psa 55 psa 5a2 psa 5a5 psa 123 psa 153 fp80 psr 53 psr 122.5 psr 152.5 psr 242 psr 362 psa 242.5 fp144 psa 121.5 psa 151.5 psa 241.5 psa 361 psa 481 table 1b: type survey ring core chokes type inductivity i ln single symm. part no. coil coil lp34-3 34 h3 a? L20-7 20 h7 a lp20-7 20 h7 a lp183 2 183 h8 a filter blocks fp types the filter blocks contain, in addition to a mpp ring core, a capacitor and an attenuation resistor, capable of handling the high ripple currents seen at the input of switching regu- lators. this forms a complete external filter system opti- mised to prevent oscillations and to reduce superimposed interference voltages and currents, specially designed for use in pcb applications together with switching regulators in an a01 case size. for selection of filters refer to the type survey. table of contents page description ....................................................................... 1 filter blocks fp types ..................................................... 1 page low-loss ring core chokes l/lp-series ....................... 3 mechanical dimensions ................................................... 5
accessories filter & ring core chokes fp, l and lp series rev. sep 29, 2003 page 2 of 5 electrical data filter blocks general condition: t a = 25c unless otherwise specified table 2: filter blocks fp characteristics conditions fp38 fp80 fp144 min typ max min typ max min typ max unit i fn rated current l = 0.75 l o 442a dc u fn rated voltage t c min ... t c max 5 40 5 80 15 144 v dc r f ohmic resistance 18 20 22 18 20 22 90 95 100 my l o no load inductance i l = 0, t c min ... t c max 30 34 38 30 34 38 88 100 112 h t a ambient temperature i f = i fn ?40 80 ?40 80 ?40 95 c t c case temperature ?40 92 ?40 92 ?40 98 t s storage temperature ?40 100 ?40 100 ?55 100 for currents i f > 4 a the following derating takes place: t a max = 100 ? 1.3 i f 2 [c], t c max = 100 ? 0.49 i f 2 [c] reduction of output ripple even though switching regulators have an inherently low output ripple, certain sensitive applications need even fur- ther reduction. in such cases, the filters designed to reduce disturbances at the input, can also be used for reducing the ripple on the output voltage (even better results with regard to the ripple and dynamic control deviation can be achieved by using low-loss ring core chokes in combination with an external capacitor, see below). the output ripple can be reduced by the use of filter blocks by about 24 db. the formula for the ripple u r at the load r l is as follows: u r = 0.063 u o (ripple voltage u o is given for specific regulators in the cor- responding data section). consider, that the filter not only affects the output ripple but can also influence the voltage across the load r l in the event of load changes. the static load regulation increases with the ohmic resistance of the choke i.e. 24 mv/a for the fp 38 and fp 80 filters and 95 mv/a for the fp 144 filter. vi+ gi? vo+ go? psr r l u r u filter uio uii gi u o 12010 fig. 2 reduction of voltage interference by fp filters input interference reduction an ac ripple current can be measured at the input of any switching regulator, even if they are equipped with an input filter. depending on the types of filters used, common and/ or differential mode interferences can be reduced. they will also help to further increase the surge and burst immunity of the power supplies. the fp filters considerably increase the source impedance of the regulators superimposed interference, to a value which is normally high in comparison to the impedance of the source ( z line ). the interference currents are therefore practically independent of their source impedance. the fil- ter will reduce these currents by approximately 25 db at a frequency of 150 khz. the interference voltages at the filter input are due to the remaining interference currents flowing through the source impedance. the resulting interference voltage reduction can be seen in the following figure. for frequencies above the regulator switching frequency the attenuation will in- crease (up to 2 mhz approx.). parallel operation: when several switching regulator inputs are connected in parallel, each regulator should be equipped with a separate input filter. interconnections should only be made in front of the filter or at its input uii (i. e. the central ground point should be before or at the filter and under no circumstances at the regulator input). 0 1 2 3 4 5 6 10 20 30 40 z line [ ] source impedance 0 interference voltage reduction att. [db] inductive resistive capacitive 12009 fig. 1 interference voltage reduction with fp filters at f = 150 khz
accessories filter & ring core chokes fp, l and lp series rev. sep 29, 2003 page 3 of 5 typical application the example in figure reduction of voltage interference by fp filters shows a switching regulator operating from a bat- tery ( r i < 0.5 ? ) with long supply lines (e.g. 2 m). the result- ing superimposed interference voltage u sl may be meas- ured at the regulators input. the connection of a filter in front of the power supply will reduce this interference ac- cordingly: 1. the regulator's source impedance is mainly inductive because of the low battery impedance and the long sup- ply lines. it can be calculated as follows: l z line l ? 2 f s l line 2 l l z line l ? 2 (150 10 3 ) 10 -6 2 2 ? 3.8 ? f s : switching frequency (150 khz) l line : supply line inductance (typically 1h/m) l : length of single supply line (twice for posi- tive and negative path) fig. 3 reduction of voltage interference by fp filters vi+ gi? vo+ go? psr r l u o u filter uio uii gi u s 2 l z line 12011 2. this example shows, that with an inductive source im- pedance of 3.8 ? , the insertion of the filter results in an interference voltage reduction of approx. 18 db (see fig.: interference voltage reduction with fp filters at f = 150 khz ). 3. the original superimposed interference voltage will be reduced by a factor of approx. 8: u sf = u sl 10 ?18/20 [v] electrical data ring core chokes general condition: t a = 25c unless otherwise specified table 3: ring core chokes characteristics conditions L20-7/lp 20-7 lp34-3 lp183 min typ max min typ max min typ max unit i ln rated current 1 l = 0.75 l o 7 3 8 a dc r l ohmic resistance 5 5.5 6 18 20 22 2 2.9 2 4.2 2 5.5 my l o no load inductance i l = 0, t c min ... t c max 18 20 22 30 34 38 2 95 2 183 2 245 h d ti current specific case 0.082 0.68 0.19 k/a 2 temp. increase 1 t a amb. temperature 1 i l = i ln ?40 106 ?40 104 ?40 98 c t c case temperature ?40 110 ?40 110 ?40 110 t s storage temperature ?40 110 ?40 110 ?40 110 1 if the choke is not operating at the rated current i ln , the maximum ambient temperature t a max and the maximum direct current i l max change according to the following equations: i l max = t c max ? t a max t a max = t c max ? i l 2 max d ti d ti low-loss ring core chokes l/lp-series the ring core chokes, in combination with a capacitor, may easily be used for application specific lc filters at the input or output of switched mode power supplies. all chokes are suitable for pcb mounting. they are either moulded into plastic cases or isolated from the pcb by means of an iso- lation pad. series l/lp20-7 and lp34-3 are intended for use as differ- ential mode filters and the current compensated choke lp183 enables attenuation of common mode interference. 80 60 40 0 20 02 6 412 8 10 14 100 7 3 75 lp34-3 lp183 l/lp20-7 12012 l / l o [%] i ln i ln i l [a] fig. 4 choke inductance versus current
accessories filter & ring core chokes fp, l and lp series rev. sep 29, 2003 page 4 of 5 input interference reduction using l- or lp-series chokes together with an additional external capacitor a similar attenuation can be achieved as with filter blocks. the capacitor between the choke and the converter input is necessary in order to avoid possible oscil- lations caused by the negative input impedance of the regu- lator. this phenomenon could cause the input voltage to leave the specified regulator input range. the relatively high ripple current flowing through the capacitor must be considered for the design. refer also to: technical informa- tion: installation & application . the current compensated choke lp183 has a high perme- ability ring core with two identical separate windings. the normal operating current will only see the small stray in- ductance between the windings. however common mode interference will be blocked by the full inductance of the choke. fig. 7 low-loss ring core choke with external capacitor (c ex approx. 1000 f) used as output filter reduction of output ripple even though switching regulators have an inherently low output ripple, certain sensitive applications need even fur- ther reduction. in such cases, the low-loss ring core chokes designed to reduce disturbances at the input can also be used for reducing the ripple on the output voltage. the chokes in combination with an external capacitor can achieve even better results than the filter blocks with re- gard to the ripple and dynamic regulation. the formula for the remaining output ripple at the load r l is calculated as follows: u r = u o z c ext / z ld u o : output ripple of the regulator z cex : the impedance of the capacitor at the regu- lator's switching frequency (150 khz) corre- sponds to the equivalent series resistance (esr) of the capacitor (please refer to the corresponding data sheet). z ld =2 f s l d f s : 150 khz (regulator switching frequency) through the use of a common mode choke lp 183, the common mode noise at the output can also be further re- duced. consider that the filter not only affects the output ripple but can also influence the voltage u r across the load r l in the event of load changes. the static regulation increases with the ohmic resistance of the choke, i.e. 6 mv/a for the choke l/lp20-7 and 20 mv/a for the lp34-3. the dynamic regulation is dependent on the size of the ca- pacitor. generally, the bigger c ex the smaller is the dy- namic, however, recovery will be slower. typical application a voltage drop u rgo = r go ( i o ? i i ) is produced across the ground loop resistance r go . it is superimposed upon the regulators output voltage u o and generates the voltage u r = u o ? u r go across the load resistance r l . without an input inductance l e the current i i in the input circuit has a rela- tively high ac component with a basic frequency f s (regula- tor's switching frequency of approx. 150 khz). this alternat- ing current produces an ac voltage component across r go which is superimposed upon u rl . to prevent this phenomenon, an inductance l e can be in- serted into the input circuit. this causes the ac component of the input current to be supplied entirely from the input capacitor c e ; thus, i i is a pure direct current. c e should be wired as close as possible to the regulator's input terminals vi+ and gi?. l e and c e additionally provide protection against input tran- sients and reduce radio interference voltages. external connection of gi? and go? or connection via a common ground is not recommended. the internal voltage drop u rg in the regulator would be superimposed on the output voltage. vi+ gi? vo+ go? psr c e u o u 12014 u r r l r d l d z ld z c ext fig. 5 l/lp type chokes and capacitors used as input filter vi+ gi? vo+ go? psr u c ext 1 c ext 2 c ext 3 lp34-3 or l/lp20-7 lp183 12013 u o r l vi+ gi? vo+ go? psr r l u o u c e l e u r g r go r g u r go i o u rl 12015 fig. 6 reduction of superimposed interference voltages in grounded power supply systems, caused by ground loops
accessories filter & ring core chokes fp, l and lp series rev. sep 29, 2003 page 5 of 5 mechanical dimensions dimensions in mm. tolerances 0.2 mm unless otherwise specified fig. 10 differential mode choke lp34-3, weight 7 g fig. 9 differential mode choke L20-7, weight 30 g fig. 11 common mode choke lp183, weight 7 g 27 38.1 47.5 13.7 22 1 3.6 30 7.5 1 ? 3.8 4 6 0.8 12017 2 x 5.08 17.5 10 1 5 1 ? 1 5.08 m 2.5 ? 0.8 12018 3 ?0.5 5.08 max 14.5 7.6 13.2 7.5 max 8 ? 0.9 12019 37.8 0.5 ?1.3 1 m 2.5 0.9 x 0.56 25 0.5 min. 4.5 1 3.22 0.5 (3.22) b 3.66 10.16 15.24 (3.66) 16.6 1 4 1 2 3 4 6.8 1 b b legend: b = 5.08 mm 1 = uii (input) 2 = uio (output) 3 = gi (ground) 4 = positionin g p ins 12016 fig. 8 filter blocks fp weight 30 g european projection nuclear and medical applications - power-one products are not authorized for use as critical components in life support systems, equipment used in hazardous environments, or nuclear control systems without the express written consent of the respective divisional president of power-one, inc. technical revisions - the appearance of products, including safety agency certifications pictured on labels, may change depending on the date manufactured. specifications are subject to change without notice.
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