Accessories Filter & Ring Core Chokes FP, L and LP Series 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 forOption , and to section: Technical Information: Installation & Ap- plication. Table 1a: Type survey of FP filter blocks Table 1b: Type survey ring core chokes Filter type Matching switching Type Inductivity I Single Symm. Ln Part No. regulator type Part No. coil coil FP38 PSR 54 LP34-3 34 H3 A PSA 55 L20-7 20 H7 A PSA 5A2 LP20-7 20 H7 A PSA 5A5 PSA 123 LP183 2 183 H8 A 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 Filter Blocks FP Types The filter blocks contain, in addition to a MPP ring core, a interference voltages and currents, specially designed for capacitor and an attenuation resistor, capable of handling use in PCB applications together with switching regulators the high ripple currents seen at the input of switching regu- in an A01 case size. For selection of filters refer to the type lators. This forms a complete external filter system opti- survey. mised to prevent oscillations and to reduce superimposed Table of Contents Page Page Description ....................................................................... 1 Low-Loss Ring Core Chokes L/LP-Series ....................... 3 Filter Blocks FP Types ..................................................... 1 Mechanical Dimensions ................................................... 5 REV. SEP 29, 2003 Page 1 of 5Accessories Filter & Ring Core Chokes FP, L and LP Series Electrical Data Filter Blocks General Condition: T = 25C unless otherwise specified A Table 2: Filter blocks FP Characteristics Conditions FP38 FP80 FP144 min typ max min typ max min typ max Unit I Rated current L = 0.75 L 44 2 A DC Fn o U Rated voltage T ...T 5 40 5 80 15 144 V DC Fn C min C max R Ohmic resistance 18 20 22 18 20 22 90 95 100 m F L No load inductance I = 0, T ...T 30 34 38 30 34 38 88 100 112 H o L C min C max T Ambient temperature I = I 40 80 40 80 40 95 C A F Fn T Case temperature 40 92 40 92 40 98 C T Storage temperature 40 100 40 100 55 100 S 2 2 For currents I > 4 A the following derating takes place: T = 100 1.3 I C , T = 100 0.49 I C F A max F C max F Reduction of Output Ripple Input Interference Reduction An AC ripple current can be measured at the input of any Even though switching regulators have an inherently low switching regulator, even if they are equipped with an input output ripple, certain sensitive applications need even fur- filter. Depending on the types of filters used, common and/ ther reduction. In such cases, the filters designed to reduce disturbances at the input, can also be used for reducing the or differential mode interferences can be reduced. They will ripple on the output voltage (even better results with regard also help to further increase the surge and burst immunity of the power supplies. to the ripple and dynamic control deviation can be achieved by using low-loss ring core chokes in combination with an The FP filters considerably increase the source impedance external capacitor, see below). of the regulators superimposed interference, to a value The output ripple can be reduced by the use of filter blocks which is normally high in comparison to the impedance of the source (Z ). The interference currents are therefore by about 24 dB. The formula for the ripple u at the load R R L Line practically independent of their source impedance. The fil- is as follows: ter will reduce these currents by approximately 25 dB at a u = 0.063 u R o frequency of 150 kHz. (Ripple voltage u is given for specific regulators in the cor- o The interference voltages at the filter input are due to the responding data section). remaining interference currents flowing through the source Uii Uio impedance. The resulting interference voltage reduction 12010 Vi+ Vo+ Filter can be seen in the following figure. For frequencies above the regulator switching frequency the attenuation will in- U U U R Gi R PSR o L crease (up to 2 MHz approx.). Gi Go Parallel operation: When several switching regulator inputs are connected in parallel, each regulator should be Fig. 2 equipped with a separate input filter. Interconnections Reduction of voltage interference by FP filters 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). Consider, that the filter not only affects the output ripple but can also influence the voltage across the load R in the L inductive event of load changes. The static load regulation increases Att. dB resistive with the ohmic resistance of the choke i.e. 24 mV/A for the capacitive 12009 40 FP 38 and FP 80 filters and 95 mV/A for the FP 144 filter. 30 20 10 0 Z Line Fig. 1 0 1 2 3 4 5 6 Interference voltage reduction with FP filters at f = 150 kHz Source impedance REV. SEP 29, 2003 Page 2 of 5 Interference voltage reduction