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 (

< 0.5 Ω) with long supply lines (e.g. 2 m).The result-

ing superimposed interference voltage

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

l

Switching frequency (150 kHz)

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

U

Filter

Uio

Uii

Gi

2 • l

12011

2. This example shows, that with an inductive source im-

pedance 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:

Electrical Data Ring Core Chokes

General Condition:

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

7

3

8

A DC

Ohmic resistance

5

5.5

6

18

20

22

2

mý

No load inductance

18

20

22

30

34

38

2

µH

Current specific case

0.082

0.68

0.19

–40

106

–40

104

–40

98

°C

Case temperature

–40

110

–40

110

–40

110

Storage temperature

–40

110

–40

110

–40

110

change according to the following equations:

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

Fig. 4

Choke inductance versus current