Accessories

Filter & Ring Core Chokes FP, L and LP Series

REV. SEP 29, 2003

Page 2 of 5

Electrical Data Filter Blocks

General Condition:

Table 2: Filter blocks FP

Characteristics

Conditions

FP38

FP80

FP144

min

typ

max

min

typ

max

min

typ

max

Unit

Rated current

44

2

A DC

Rated voltage

5

40

5

80

15

144

V DC

Ohmic resistance

18

20

22

18

20

22

90

95

100

mý

No load inductance

30

34

38

30

34

38

88

100

112

µH

Ambient temperature

–40

80

–40

80

–40

95

°C

Case temperature

–40

92

–40

92

–40

98

Storage temperature

–40

100

–40

100

–55

100

For currents

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

is as follows:

(Ripple voltage

responding data section).

Consider, that the filter not only affects the output ripple but

can also influence the voltage across the load

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

U

Filter

Uio

Uii

Gi

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 (

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

Source impedance

0

Att. [dB]

inductive

resistive

capacitive

12009

Fig. 1

Interference voltage reduction with FP filters at f = 150 kHz