Accessories Filter & Ring Core Chokes FP, L and LP Series Description These Filters and chokes are designed to reduce input interference and/or output ripple voltages occurring in applications 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 magnetisation 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 considerably exceed the rated current, by accepting a corresponding gradual loss of inductance (unlike ferrite core chokes where inductance rapidly decreases above a certain DC magnetising level). In applications where switching regulators have long supply lines, filters and chokes are used in order to prevent oscillations caused by their negative input impedance. For further information refer also to switching regulator data for "Option L", and to section: Technical Information: Installation & Application. Table 1a: Type survey of FP filter blocks Table 1b: Type survey ring core chokes Filter type Part No. Matching switching regulator type Type Inductivity Part No. FP38 PSR 54 PSA 55 PSA 5A2 PSA 5A5 PSA 123 PSA 153 LP34-3 34 µH 3A • L20-7 20 µH 7A • LP20-7 20 µH 7A • LP183 2 ∞ 183 µH 8A FP80 PSR 53 PSR 122.5 PSR 152.5 PSR 242 PSR 362 PSA 242.5 FP144 PSA PSA PSA PSA PSA ILn Single Symm. coil coil • 121.5 151.5 241.5 361 481 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 regulators. This forms a complete external filter system optimised to prevent oscillations and to reduce superimposed Table of Contents 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. Page Page Description ....................................................................... 1 Filter Blocks FP Types ..................................................... 1 Low-Loss Ring Core Chokes L/LP-Series ....................... 3 Mechanical Dimensions ................................................... 5 REV. SEP 29, 2003 Page 1 of 5 Accessories Filter & Ring Core Chokes FP, L and LP Series Electrical Data Filter Blocks General Condition: TA = 25°C unless otherwise specified Table 2: Filter blocks FP Characteristics Conditions min FP38 typ max min FP80 typ max min FP144 typ max IFn Rated current L = 0.75 Lo UFn Rated voltage TC min...TC max RF Ohmic resistance 18 Lo No load inductance IL = 0, TC min...TC max 30 TA Ambient temperature IF = IFn –40 TC Case temperature –40 92 –40 92 –40 98 TS Storage temperature –40 100 –40 100 –55 100 4 5 4 40 5 20 22 18 34 38 30 80 –40 2 80 15 20 22 90 34 38 88 80 –40 Unit A DC 144 V DC 95 100 mý 100 112 µH 95 °C For currents IF > 4 A the following derating takes place: TA max = 100 – 1.3 • IF2 [°C], TC max = 100 – 0.49 • IF2 [°C] Input Interference Reduction Reduction of Output Ripple 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. Even though switching regulators have an inherently low output ripple, certain sensitive applications need even further 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 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 (ZLine). The interference currents are therefore practically independent of their source impedance. The filter 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 increase (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). inductive resistive capacitive Interference voltage reduction Att. [dB] 40 12009 The output ripple can be reduced by the use of filter blocks by about 24 dB. The formula for the ripple uR at the load RL is as follows: uR = 0.063 • uo (Ripple voltage uo is given for specific regulators in the corresponding data section). Vo+ Vi+ U Uo PSR Gi– Uii Filter Uio Gi 12010 UR RL Go– Fig. 2 Reduction of voltage interference by FP filters Consider, that the filter not only affects the output ripple but can also influence the voltage across the load RL 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. 30 20 10 Z Line [ ] 0 0 1 REV. SEP 29, 2003 3 2 4 Source impedance 5 6 Fig. 1 Interference voltage reduction with FP filters at f = 150 kHz Page 2 of 5 Accessories Filter & Ring Core Chokes FP, L and LP Series Typical Application The example in figure Reduction of voltage interference by FP filters shows a switching regulator operating from a battery (Ri < 0.5 Ω) with long supply lines (e.g. 2 m). The resulting superimposed interference voltage USL may be measured at the regulators input. The connection of a filter in front of the power supply will reduce this interference accordingly: 2. This example shows, that with an inductive source impedance of 3.8 Ω, 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: 1. The regulator's source impedance is mainly inductive because of the low battery impedance and the long supply lines. It can be calculated as follows: USF = USL • 10 –18/20 [V] 2•l Uii l ZLine l ≅ 2 π • fS • LLine • 2 l l ZLine l ≅ 2 π • (150 • 103) • 10-6 • 2 • 2 ≅ 3.8 Ω Us ZLine U fS : Switching frequency (150 kHz) LLine : Supply line inductance (typically 1µH/m) l: Length of single supply line (twice for positive and negative path) Uio Filter 12011 Vo+ Vi+ Gi– RL Uo PSR Gi Go– Fig. 3 Reduction of voltage interference by FP filters Low-Loss Ring Core Chokes L/LP-Series 12012 100 LP183 80 75 LP34-3 60 L/LP20-7 ILn Series L/LP20-7 and LP34-3 are intended for use as differential mode filters and the current compensated choke LP183 enables attenuation of common mode interference. L /Lo [%] ILn 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 isolation pad. 40 20 Fig. 4 Choke inductance versus current 0 0 2 3 4 6 7 8 10 12 14 IL [A] Electrical Data Ring Core Chokes General Condition: TA = 25°C unless otherwise specified Table 3: Ring core chokes Characteristics Conditions 1 L20-7/LP 20-7 min typ max L = 0.75 Lo min LP34-3 typ max min LP183 typ max ILn Rated current RL Ohmic resistance Lo No load inductance D TI Current specific case temp. increase 1 TA Amb. temperature 1 –40 106 –40 104 –40 98 TC Case temperature –40 110 –40 110 –40 110 TS Storage temperature –40 110 –40 110 –40 110 IL = 0, TC min...TC max 7 3 8 A DC 5 5.5 6 18 20 22 2×2.9 2×4.2 2×5.5 mý 18 20 22 30 34 38 2×95 2×183 2×245 µH 0.19 K/A2 0.082 IL = ILn Unit 0.68 1 If °C the choke is not operating at the rated current ILn, the maximum ambient temperature TA max and the maximum direct current IL max change according to the following equations: TC max –TA max IL max = TA max = TC max – IL2 max • D TI D TI REV. SEP 29, 2003 Page 3 of 5 Accessories Filter & Ring Core Chokes FP, L and LP Series Input Interference Reduction Reduction of Output Ripple 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 oscillations caused by the negative input impedance of the regulator. 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 Information: Installation & Application. Even though switching regulators have an inherently low output ripple, certain sensitive applications need even further 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 regard to the ripple and dynamic regulation. The current compensated choke LP183 has a high permeability ring core with two identical separate windings. The normal operating current will only see the small stray inductance between the windings. However common mode interference will be blocked by the full inductance of the choke. LP183 LP34-3 or L/LP20-7 U 12013 Vo+ Vi+ Uo PSR Cext 1 Cext 2 Cext 3 Gi– RL Go– Fig. 5 L/LP type chokes and capacitors used as input filter Typical Application A voltage drop UrGo = rGo • (Io – Ii) is produced across the ground loop resistance rGo. It is superimposed upon the regulators output voltage Uo and generates the voltage UR = Uo – Ur Go across the load resistance RL. Without an input inductance Le the current Ii in the input circuit has a relatively high AC component with a basic frequency fs (regulator's switching frequency of approx. 150 kHz). This alternating current produces an AC voltage component across rGo which is superimposed upon URL. To prevent this phenomenon, an inductance Le can be inserted into the input circuit. This causes the AC component of the input current to be supplied entirely from the input capacitor Ce; thus, Ii is a pure direct current. Ce should be wired as close as possible to the regulator's input terminals Vi+ and Gi–. The formula for the remaining output ripple at the load RL is calculated as follows: UR = uo • ZC ext/ZLD uo : Output ripple of the regulator ZCex: The impedance of the capacitor at the regulator's switching frequency (150 kHz) corresponds to the equivalent series resistance (ESR) of the capacitor (please refer to the corresponding data sheet). ZLD = 2 π • fS • LD fS: 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 reduced. Consider that the filter not only affects the output ripple but can also influence the voltage UR across the load RL 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 capacitor. Generally, the bigger Cex the smaller is the dynamic, however, recovery will be slower. RD PSR Gi– ZLD ZC ext 12014 Vo+ Vi+ U LD Uo Ce UR RL Go– Fig. 7 Low-loss ring core choke with external capacitor (Cex approx. 1000 µF) used as output filter Le and Ce additionally provide protection against input transients and reduce radio interference voltages. External connection of Gi– and Go– or connection via a common ground is not recommended. The internal voltage drop UrG in the regulator would be superimposed on the output voltage. 12015 Le U PSR Ur G Ce Gi– rG Uo RL URL Go– rGo REV. SEP 29, 2003 Io Vo+ Vi+ Ur Go Fig. 6 Reduction of superimposed interference voltages in grounded power supply systems, caused by ground loops Page 4 of 5 Accessories Filter & Ring Core Chokes FP, L and LP Series Mechanical Dimensions European Projection 7.5 ±1 ø 3.8 3.6 b (3.22) 4 13.7 6 b 3.66 b 30 15.24 12017 0.9 x 0.56 3.22 ±0.5 10.16 1 4 Legend: b = 5.08 mm 1 1 = Uii (input) 2 = Uio (output) 3 = Gi (ground) 4 = Positioning pins 22 ±1 3 2 ø1.3 ±1 37.8 ±0.5 min. 4.5 4 12016 16.6 ±1 6.8 ±1 M 2.5 25 ±0.5 (3.66) Dimensions in mm. Tolerances ±0.2 mm unless otherwise specified 0.8 Fig. 8 Filter blocks FP weight 30 g 27 38.1 47.5 Fig. 9 Differential mode choke L20-7, weight 30 g max 8 5.08 max 14.5 ø1 12019 ø 0.8 5 ±1 1 10 12018 M 2.5 3 –0.5 ø 0.9 2 x 5.08 17.5 Fig. 10 Differential mode choke LP34-3, weight 7 g 7.6 13.2 5.08 7.5 Fig. 11 Common mode choke LP183, weight 7 g 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. REV. SEP 29, 2003 Page 5 of 5