www.cd4power.com

NPH15S SERIES

Isolated 15W Single Output DC/DC Converters

EMC FILTERING AND SPECTRA

FILTERING

The module includes a basic level of filtering, sufficient for many applications. Where lower noise levels are desired, filters can easily be added to achieve any required

noise performance.

A DC/DC converter generates noise in two principle forms: that which is radiated from its body and that conducted on its external connections. There are three separate

modes of conducted noise: input differential, output differential and input-output.

This last appears as common mode at the input and the output, and cannot therefore be removed by filtering at the input or output alone. The first level of filtering is to

connect a capacitor between input and output returns, to reduce this form of noise. It typically contains high harmonics of the switching frequency, which tend to appear

as spikes on surrounding circuits. The voltage rating of this capacitor must match the required isolation voltage. (Due to the great variety in isolation voltage and required

noise performance, this capacitor has not been included within the converter.)

Input ripple is a voltage developed across the internal Input decoupling capacitor. It is therefore measured with a defined supply source impedance. Although simple series

inductance will provide filtering, on its own it can degrade the stability. A shunt capacitor is therefore recommended across the converter input terminals, so that it is fed

from a low impedance.

If no filtering is required, the inductance of long supply wiring could also cause a problem, requiring an input decoupling capacitor for stability. An electrolytic will perform

well in these situations. The input-output filtering is performed by the common-mode choke on the primary. This could be placed on the output, but would then degrade the

regulation and produce less benefit for a given size, cost, and power loss.

Radiated noise is present in magnetic and electrostatic forms. The latter is suppressed by the metal case, which is connected to the output return, typically a zero-volt

point. Thanks to the small size of these units, neither form of noise will be radiated “efficiently”, so will not normally cause a problem. Any question of this kind usually

better repays attention to conducted signals.

EMC FILTER AND VALUES TO OBTAIN SPECTRA AS SHOWN

Component reference

C1

C2

C3

C4

L1

L2

L3

NPH15S2403

10µF 100V

2.2µF 63V

47µF 63V

10µF 25V

C&D 18R333C

33µH 2A

C&D 18R472C

4.7µH 5.35A

NPH15S2405

10µF 100V

2.2µF 63V

47µF 63V

10µF 25V

C&D 18R333C

33µH 2A

C&D 18R103C

10µH 3.45A

NPH15S2412

10µF 100V

2.2µF 63V

Not required

10µF 25V

C&D 18R333C

33µH 2A

C&D 18R333C

33µH 2.00A

NPH15S2415

10µF 100V

2.2µF 63V

47µF 63V

10µF 25V

C&D 18R333C

33µH 2A

C&D 18R333C

33µH 2.00A

NPH15S4803

10µF 100V

Not required

Not required

10µF 25V

C&D 18R104C

100µH 1.2A

C&D 18R472C

4.7µH 5.35A

NPH15S4805

10µF 100V

Not required

Not required

10µF 25V

C&D 18R104C

100µH 1.2A

C&D 18R103C

10µH 3.45A

NPH15S4812

10µF 100V

Not required

Not required

10µF 25V

C&D 18R104C

100µH 1.2A

C&D 18R333C

33µH 2.00A

NPH15S4815

10µF 100V

Not required

Not required

10µF 25V

C&D 18R104C

100µH 1.2A

C&D 18R333C

33µH 2.00A

C1, C2 & C4 : Electrolytic capacitors

C3 : Polyester or ceramic capacitor

EMC Spectra red limit line is EN 55022 curve B Quasi-peak average limit.